Engines and Clutches
EPA07 Aftertreatment System (ATS)
On-road diesel engines built after December 31, 2006, are required to meet EPA07 guidelines for reduced exhaust emissions of particulate matter and nitrogen oxides (NOx). NOx is limited to just over 1 gram per brake horsepower hour (g/bhp-hr), and particulate matter cannot exceed 0.01 g/bhp-hr.
EPA07-compliant engines require ultralow-sulfur diesel (ULSD) fuel, and they should never be run on fuel with sulfur content higher than 15 ppm. In addition, they require low-ash engine oil. The following guidelines must be followed, or the warranty may be compromised.
Use ultralow-sulfur diesel (ULSD) with 15 ppm sulfur content or less, based on ASTM D2622 test procedure.
Do not use fuel blended with used engine lube oil.
Engine lube oil must have a sulfated ash level less than 1.0 wt %, meeting the API CJ-4 index specifications.
IMPORTANT: Using non-specification fuels or oils can lead to shortened diesel particulate filter (DPF) cleaning or exchange intervals. For example, using CI-4+ oil with 1.3% sulfated ash (30% more ash content) may result in the need for DPF cleaning or exchange 20 to 30% sooner than would normally be required.
The "exhaust system" in EPA07-compliant vehicles is called the aftertreatment system (ATS). The ATS varies according to engine manufacturer and vehicle configuration, but instead of a muffler, an aftertreatment system has a device that outwardly resembles a muffler, called the aftertreatment device (ATD).
IMPORTANT: See the manufacturer's engine operation manual for complete details and operation of the aftertreatment system.
Inside the ATD on Mercedes-Benz, Detroit Diesel, and Cummins engines, the exhaust first passes over the diesel oxidation catalyst (DOC), then it passes through the DPF, which traps soot particles. If exhaust temperature is high enough, the trapped soot is reduced to ash, in a process called passive regeneration (regen). Passive regeneration occurs as the vehicle is driven normally under load; the driver is not even aware that it is happening. The harder an EPA07 engine works, the better it disposes of soot, as the exhaust heat alone is enough to burn the soot to ash. Over the course of a workday, however, passive regeneration cannot always keep the ATD filter clean, so the filter must undergo active regeneration . In active regeneration, extra fuel is injected into the exhaust stream to superheat the soot trapped in the DPF and turn it to ash. Active regeneration happens only when the vehicle is moving above a certain speed, determined by the engine manufacturer. Consult manufacturers' documentation for details.
Both active and passive regeneration happen automatically, without driver input.
NOTE: Caterpillar engines do not use a DOC; CAT engines burn diesel fuel at the regeneration head to superheat the exhaust and burn the trapped soot to ash. Engine software monitors and controls this process.
Only when operating conditions do not allow for ATD filter cleaning by at-speed active or passive regeneration, the vehicle may require a parked regeneration . The vehicle must be standing still, and the driver must initiate the parked regen. Completing a parked regen takes 20 minutes to an hour, depending on ambient conditions.
DANGER
The warning lamps in the driver message center alert the driver of a regen in progress, high exhaust temperatures, the need to perform a parked regen either soon or immediately, and of an engine fault that affects the emissions.
A slow (10-second) flashing of the high exhaust system temperature (HEST) lamp indicates that a parked regeneration is in progress, and the engine's high idle speed is being controlled by the engine software, not the driver.
A steadily illuminated high temperature (HEST) lamp alerts the operator of high exhaust temperature during the regeneration process, if vehicle speed is below 5 mph (8 km/h). See Fig. 7.1 . The HEST lamp does not signify the need for any kind of vehicle or engine service; it only alerts the vehicle operator of high exhaust temperatures. Make sure the engine exhaust pipe outlet is not directed at any person, or at any surface or material that will melt, burn, or explode.
Fig. 7.1, High Exhaust System Temperature (HEST) Lamp
WARNING
A steadily illuminated yellow diesel particulate filter (DPF) lamp indicates that a regen may be required soon. Bring the vehicle to highway speeds to allow for an active regen, or a parked regen should be scheduled for the earliest convenient time. See Fig. 7.2 . A DPF lamp blinking at the same time as a steadily illuminated yellow Check Engine lamp, indicates that a parked regen must be performed immediately, or an engine derate will occur. If the red Stop Engine lamp illuminates with the blinking DPF lamp and the Check Engine lamp, a parked regen must occur or an engine shutdown will occur. Park the vehicle and perform a parked regen. See Fig. 7.3 .
Fig. 7.2, Diesel Particulate Filter (DPF) Status Lamp
- 1. Stop Engine Override Switch
- 2. Amber Check Engine Warning Lamp
- 3. Red Stop Engine Lamp
Fig. 7.3, Engine Lamps
A solid yellow malfunction indicator lamp (MIL) indicates an engine fault that affects the emissions. See Fig. 7.4 .
When diesel particulate filter servicing is needed, it must be performed by an authorized technician, and a record must be maintained for warranty purposes. The record must include:
date of cleaning or replacement;
vehicle mileage;
particulate filter part number and serial number.
Fig. 7.4, Malfunction Indicator Lamp (MIL)
The regen switch ( Fig. 7.5 ), located on the dash, is used to initiate a parked regen of the aftertreatment device.
Fig. 7.5, Regen Switch
NOTE: The regen switch can start a parked regen only when at least one of two conditions exists: either the DPF light is illuminated, or the engine software calls for it. If neither of those conditions exist, the regen switch cannot cause a regeneration to happen.
WARNING
To initiate a parked regen, perform the following steps.
1.
Park the vehicle away from all flammable materials, put the transmission in neutral, and set the parking brake.
2.
Start and warm the engine until the coolant temperature is at least 150°F (66°C).
3.
Lift the regen request switch guard and press and hold the yellow button for five seconds. As the regen process is initiated, engine rpm increases and the HEST lamp illuminates to indicate extremely high exhaust temperatures.
IMPORTANT: The driver is responsible forensuring,during the entire regen cycle, that anything that could be harmed by exposure to high heat does not come in contact with theexhaustgases flowing from the outlets.
4.
The regen cycle will finish after 20 to 60 minutes, at which time engine idle speed drops to normal and the vehicle can be driven normally. The HEST lamp is extinguished when vehicle speed exceeds 5 mph (8 km/h) or the system has cooled to normal operating temperature.
5.
To stop a parked regen at any time during the process:
depress the clutch pedal, brake pedal, or accelerator pedal;
press and hold the regen inhibit switch until idle returns to normal;
shut down the engine.
The regen-inhibit switch provides additional control over the aftertreatment regeneration process. The inhibit switch will stop a regeneration cycle in progress, and prevent the start of a regeneration cycle until the switch is no longer active. See Fig. 7.6 .
Fig. 7.6, Regen-Inhibit Switch
DD15 Heavy-Duty Engine
See Chapter 2 of this manual for information on the DDEC VI operator controls. See the Detroit Diesel DD15 Engine Operator's Guide for complete details of engine operation.
Engine Protection
An engine protection system monitors all engine sensors and electronic components, and recognizes system malfunctions. If a critical fault is detected, an amber Check Engine warning lamp and a red Stop Engine lamp illuminate. See Fig. 7.3 .
The standard parameters that are monitored for engine protection are: low coolant level, high coolant temperature, low oil pressure, and high oil temperature.
Amber Check Engine Warning Lamp
When the amber Check Engine warning lamp comes on for any reason, the vehicle can still be operated, and the driver can proceed to the required destination. See Fig. 7.3 . This condition should be reported to an authorized service center as soon as possible.
Red Stop Engine Lamp
When the red Stop Engine lamp comes on, the computer has detected a major malfunction in the engine that requires immediate attention. See Fig. 7.3 . It is the operator's responsibility to shut down the engine to avoid serious damage. This system features a 30-second, stepped-down power-shutdown sequence, or an immediate emergency-running mode, in the event that a major engine malfunction occurs. The conditions that will cause the red Stop Engine lamp to come on are:
high coolant temperature
loss of coolant
high oil temperature
low oil pressure
auxiliary shutdown
Stop Engine Override Switch
In the event that the vehicle is operating in a critical location when a shutdown is initiated, a Stop Engine Override (SEO) switch can be used to override the shutdown sequence. See Fig. 7.3 . This override resets the shutdown timer, restoring power to the level when the red stop engine lamp was illuminated. The switch must be recycled after five seconds to obtain a subsequent override.
CAUTION
DDEC VI Driving Tips
Accelerating the Vehicle
The accelerator pedal was designed to communicate "percentage" of accelerator pedal travel to the engine MCM. A throttle characteristic you may need time to get used to, is the DDEC limiting speed governor. This allows the driver to command total engine response between idle and rated speed, such as accelerating at half throttle—an advantage when driving under slippery conditions. To obtain 100 percent fueling at any speed, the accelerator pedal must be depressed to the fully pressed position.
Shifting
Depending on your transmission model, the gear split may vary from 400 to 500 rpm. The electronic governor provides almost no overrun capability; if the transmission is downshifted too early, you will experience a temporary loss of pulling power until the engine speed falls below rated speed. In general, when using a 9-speed transmission, you should always downshift between 1000 and 1100 rpm. This is true even on steep grades with heavy loads. When using an 18-, 15-, or 13-speed transmission, you will need to downshift at an rpm that allows "less than rated" rpm, before throttle application in the next gear down. You may want to limit engine speed to 1900 rpm in all gears.
The DD15 engine provides horsepower through 2100 rpm, but fuel economy is not as efficient above 1800 rpm. If you decide to drive at lower rpm for improved fuel economy, don't let different engine noises throw you off guard. The DD15 engine sounds quiet at 1400 rpm, almost as if it had quit pulling. If you had a boost gauge to look at while driving, you would notice the turbocharger maintaining steady intake manifold pressure, even as rpm falls. Depending on the air intake arrangement, you may also hear a "chuffing" sound as the engine starts to pull hard at lower rpm. This is normal, and caused by the velocity changes of the air flow within the air intake plumbing. Electronic engines can actually deliver more fuel at lower engine speeds than at rated speed.
The DD15 engine has been designed for a very quiet operation, but the air flow may be noticeable to the tuned attentive ear. The turbocharger operates at higher boost pressure, forcing exhaust to flow through the exhaust gas recirculation plumbing. In some situations the driver may believe they have experienced a charge air cooler system leak. Even while connecting trailer lights and air hoses, the driver may hear a different tone (exhaust and under hood with the engine idling). If equipped with a turbo boost gauge, the driver may occasionally note the intake manifold pressure exceeds 35 psi (241 kPa).
Idling
The common belief that idling a diesel engine causes no engine damage is wrong. Idling produces sulfuric acid, that is absorbed by the lubricating oil, and eats into bearings, rings, valve stems, and engine surfaces. If you must idle the engine for cab heat or cooling, the high idle function of the cruise control switches should be used. An idle speed of 900 rpm should be enough to provide cab heat in above freezing ambient temperatures.
Cold-Weather Operation
Precautions must be taken during cold weather to protect your engine. Special cold-weather handling is required for fuel, engine oil, coolant, and batteries. The engine does not require starting aids down to 50°F (10°C). A grid heater is included for temperatures between 50°F (10°C) and –4°F (–20°C). Temperatures below –4°F (–20°C), will require a grid heater, block heater, and oil pan heater.
CAUTION
A winterfront may be used to improve cab heating. At least 25 percent of the grill opening should remain open in sectioned stripes that run perpendicular to the charge air cooler tube flow direction. This assures even cooling across each tube, and reduces header-to-tube stress and possible failure. Winterfronts should only be used when the ambient temperature remains below 10°F (–12°C).
Driving on Flat, Dry Pavement
Use the following guidelines when driving on flat, dry pavement.
If driving on flat, dry, open stretches, with a light load, place the progressive braking switch in the LOW position.
If you find you are still using the service brakes, move the switch to a higher position until you do not need to use the service brakes to slow the vehicle.
If you are carrying a heavier load and road traction is good, move the progressive braking switch to the HIGH position.
Check your progressive braking switch often for proper position, since road conditions can change quickly. Never skip a step when operating the progressive braking switch. Always go from OFF to LOW, and then to a higher position.
Descending a Long, Steep Grade
An explanation of "control speed" may be helpful in understanding how to use the engine brake system while descending a grade. Control speed is the constant speed at which the forces pushing the vehicle forward on a grade, are equal to the forces holding it back, without using the vehicle service brakes. In other words, this is the speed the vehicle will maintain without using the service brakes or throttle.
CAUTION
Use the following guidelines when descending a long, steep grade.
Before beginning the descent, determine if your engine brake system is operating properly, by lifting your foot briefly off the accelerator pedal. You should feel the system activate.
Ensure the progressive braking switch is in the appropriate power position. Check your progressive braking switch often for proper position, since road conditions can change quickly. Never skip a step when operating the progressive braking switch. Always go from OFF to LOW and then to a higher position when on slippery roads.
Do not exceed the safe control speed of your vehicle. Example: You could descend a 6 percent grade, under control at 10 mph (16 km/h) without an engine brake, but at 25 mph (40 km/h) it requires an engine brake. You could not descend that same hill at 50 mph (80 km/h) and still expect to remain under control. Know how much slowing power your engine brake can provide before descending hills, and do not exceed a safe control speed.
Driving on Wet or Slippery Pavement
WARNING
on wet or slippery pavement
when driving without a trailer (bobtailing) or pulling an empty trailer
if the tractor drive wheels begin to lock, or there is fishtail motion after the engine brake is activated
NOTE: On single trailers or combinations, a light air application of the trailer brakes may be desirable to help keep the trailer stretched out. Follow the manufacturer's recommended operating procedure when using the trailer brakes.
On wet or slippery pavement, start with the main switch in the OFF position and use the gear you would normally use under these conditions. If the vehicle is maintaining traction, place the selective braking switch in the LOW position and turn ON the engine brake system. If the drive wheels are maintaining traction and you desire greater slowing power, move the braking switch to the next higher position. However, if the tractor drive-wheels begin to lock, or there is a fishtail motion, turn the engine brake system OFF immediately and do not activate it until road conditions improve.
Check your progressive engine braking switch often for proper position, since road conditions can change quickly. Never skip a step when operating the progressive braking system. Always go from OFF to LOW and then to a higher position. See Chapter 2 for the proper operation of the engine brake.
Engine Starting—CAT, Cummins, DDE S60, M-B
Normal Starting
NOTE: Before starting the engine, read Chapter 2 for detailed information on how to read the instruments and operate the controls. Read the operating instructions in the engine manufacturer's operating manual before starting the engine.
IMPORTANT: Ring gear and starter pinion damage caused by improper starting procedures is not warrantable.
CAUTION
Prestart
NOTE: These prestart steps apply to all the following engines.
1.
Before engine start-up, perform the engine pretrip inspection and daily maintenance checks in Chapter 11 .
2.
Apply the parking brake.
3.
For manual transmissions, place the transmission in neutral and step on the clutch pedal. Do not push the accelerator pedal.
3.
NOTE: On vehicles equipped with a neutral start switch, the transmission must be in neutral before the engine can be started. For air start systems, check the air supply before starting the engine. There must be 100 psi (689 kPa) of air pressure available.
Starting Precautions
CAUTION
NOTE: Some starters are equipped with optional overcrank protection. If overcranking occurs, a thermostat breaks the electrical circuit to the starter motor until the motor has cooled.
CAUTION
WARNING
Caterpillar
NOTE: Before doing these steps, do the steps in "Prestart."
1.
Turn the ignition switch to the on position. See Fig. 7.7 . All the electronic gauges on the ICU (instrumentation control unit) complete a full sweep of their dials, the warning and indicator lights light up, and the buzzer sounds for 3 seconds.
Fig. 7.7, Ignition Switch Positions
NOTE: The engine electronics supply the correct amount of fuel for starting the engine. Pedal pressure is unnecessary.
2.
Turn the ignition switch to the start position. Do not press down on the throttle pedal. Release the switch the moment the engine starts.
2.1
If the engine does not start after 30 seconds of cranking, turn the ignition switch off.
NOTE: Some starters are equipped with optional overcrank protection. If overcranking occurs, a thermostat breaks the electrical circuit to the starter motor until the motor has cooled.
2.2
Wait two minutes to allow the starter motor to cool. Turn the ignition switch back to the on position and try again to start the engine.
2.3
As soon as the engine starts, release the ignition switch, allowing the engine to run at a slow idle.
CAUTION
3.
Caterpillar C–10/C–12/C–15/C–16 engines may be operated at low load and speed once the engine oil pressure has reached 10 to 20 psi (69 to 138 kPa). Caterpillar 3406E engines may be operated at low load and speed once the engine oil pressure has reached 18 psi (124 kPa).
4.
When the engine has reached the normal operating temperature of 189°F (87°C), the engine may be operated at full load.
Detroit Diesel S60
NOTE: Before doing these steps, do the steps in "Prestart."
1.
Turn the ignition switch to the on position. See Fig. 7.7 . All the electronic gauges on the ICU (instrumentation control unit) complete a full sweep of their dials, the warning and indicator lights light up, and the buzzer sounds for three seconds.
2.
When all the indicators go out, turn the ignition switch to the start position. Without touching the throttle pedal, start the engine. If the engine won't start within 15 seconds, release the ignition switch and allow the starter motor to cool.
IMPORTANT: If the engine won't start, check the main engine power fuses. The fuses are located along the main engine electrical harness on the left frame rail, near the batteries. If the fuses are blown, replace the fuses. Be sure to find the cause of the blown fuses as soon as possible.
NOTE: Some starters are equipped with optional overcrank protection. If overcranking occurs, a thermostat breaks the electrical circuit to the starter motor until the motor has cooled.
WARNING
3.
Check the oil pressure gauge immediately after starting the engine.
4.
If no pressure registers within 10 to 15 seconds or the ENGINE PROTECT indicator comes on, shut down the engine and check the lubricating oil system.
CAUTION
5.
Idle the engine for about five minutes at 1000 rpm before operating the engine under load.
Mercedes-Benz
NOTE: Before doing these steps, do the steps in "Prestart."
CAUTION
1.
Turn the ignition switch to the on position. See Fig. 7.7 . All the electronic gauges on the ICU (instrumentation control unit) complete a full sweep of their dials, the warning and indicator lights light up, and the buzzer sounds for three seconds.
IMPORTANT: On vehicles equipped with an intake air preheater, the INTAKE HEATER indicator stays on for a minimum of two seconds, regardless of coolant temperature. Wait until the INTAKE HEATER indicator goes out before attempting to start the engine.
2.
Turn the ignition switch to the start position. Without touching the throttle pedal, start the engine.
NOTE: Some starters are equipped with optional overcrank protection. If overcranking occurs, a thermostat breaks the electrical circuit to the starter motor until the motor has cooled.
3.
It is not necessary to idle the engine before engaging or starting the operation, but load should be applied gradually during the warm-up period until the oil temperature reaches 140°F (60°C).
4.
Check the oil pressure gauge for any drop in lubricating oil pressure or mechanical malfunction in the lubricating oil system. Minimum oil pressure at idle is 7 psi (50 kPa).
CAUTION
Cold-Weather Starting
Modern electronic engines do not normally require special starting aids. At low temperatures, oil pan heaters or water jacket heaters are sometimes used to assist in starting.
Caterpillar
WARNING
Turn the ignition switch to the on position. See Fig. 7.7 .
If the engine doesn't start after 30 seconds of cranking, turn the key to the off position and wait two minutes; then repeat the starting procedure.
If the coolant temperature is less than 64°F (18°C), the engine will start up in the cold-start strategy. This reduces the amount of fuel available to the injectors, advances the timing, and controls white smoke emissions. The engine remains in the cold-start strategy until the coolant temperature rises above 64°F (18°C), or until it has been running for 12 minutes.
IMPORTANT: Do not move the vehicle when it is in the cold-start strategy. Power will be noticeably reduced.
After a cold engine start of less than 64°F (18°C), Caterpillar electronic engines automatically idle at 800 rpm (for C–10 and C–12 engines), or 600 rpm (for 3406E, C–15, and C–16 engines). These electronic engine systems will adjust the idle speed to 700 to 750 rpm when the engine is warm enough to drive the vehicle.
Detroit Diesel S60
The engine may require the use of a cold-weather starting aid if the outside temperature falls below 40°F (4°C).
Turn the ignition switch to the on position and start the engine.
If the engine doesn't start after 30 seconds of cranking, turn the key to the off position and wait two minutes; then repeat the starting procedure.
Run the engine slightly above idle until oil pressure shows on the gauge. If oil pressure doesn't show on the gauge within 30 seconds of starting, turn the key to the off position and wait one minute; then repeat the starting procedure.
Mercedes-Benz
CAUTION
The intake air preheater is activated by turning the ignition switch to the on position. See Fig. 7.7 . If the engine is at normal temperature, the INTAKE HEATER indicator goes out after two seconds.
If the temperature is low enough to require the heater, the INTAKE HEATER indicator stays on while the intake air preheater warms up. After the indicator goes out, start the engine. If the engine doesn't start after about 30 seconds of cranking, turn the key to the off position and wait two minutes; then repeat the starting procedure.
NOTE: If the engine doesn't start on the second try, wait at least five minutes before using the intake air preheater again.
Starting After Extended Shutdown or Oil Change—CAT, Cummins, DDE S60, M-B
An engine in storage for an extended period of time (over winter, for example) may accumulate water in the oil pan. Oil diluted by water cannot provide adequate bearing protection at start-up. For this reason, change the engine oil and filters after extended storage.
Do the following steps after an oil change or after the engine has been shut down for more than three days:
1.
Make sure the transmission is filled with the correct type of fluid, as recommended by the transmission manufacturer.
2.
Make sure the fuel tank is full. If air has entered the fuel system, prime the fuel system, using the engine manufacturer's instructions.
3.
If the engine is equipped with a fuel/water separator, drain off any accumulated water.
4.
Check the drive belts to make sure they are in good condition and properly adjusted. Replace any drive belts that are cracked, worn, or glazed.
5.
Check the turbocharger for signs of oil or exhaust leaks. Correct any problems before starting the engine.
6.
Check the engine mounting bolts for tightness. Retighten them if necessary.
7.
Make sure the battery cable connections are clean and tight. Check that the batteries are charged.
8.
Start the engine. See "Engine Starting".
Engine Break-In—CAT, Cummins, DDE S60, M-B
Caterpillar
Every Caterpillar engine must pass a full-load operation test on a dynamometer before shipment, eliminating the need for a break-in period. Only an initial operational check is necessary.
Cummins
Cummins engines are run on a dynamometer before being shipped from the factory. They do not require a break-in period.
Detroit Diesel S60
Detroit Diesel S60 engines can be put to work upon delivery without having to follow a formal break-in schedule. The engine has been "run-in" on a factory dynamometer during performance and quality assurance tests prior to shipment.
Mercedes-Benz
Each Mercedes-Benz engine must pass a full-load operating test on a dynamometer before shipment, thereby eliminating the need for a break-in. Before running the engine for the first time, follow the instructions in Chapter 2 of the MBE4000 Engine Operator's Manual .
Engine Operation—CAT, Cummins, DDE S60, M-B
Safety and Environmental Considerations
WARNING
Operating vehicles with diesel engines in areas where there are concentrated flammable vapors (such as diesel, gasoline, natural gas, or propane fumes) can create a hazardous situation. These vapors can be drawn into the engine through the air intake, and cause engine overspeed. Be especially cautious of low-lying or closed-in areas, and always check for signs posted where flammable vapors may be present.
All diesel engines for these vehicles have been built to comply with the requirements of the Federal (U.S.) Clean Air Act. Once an engine is placed in service, the responsibility for meeting both state and local regulations is with the owner/operator.
It is extremely important to use the correct fuel for EPA07-compliant engines. The following requirements must be met, otherwise damage can occur to the aftertreatment device, and the warranty may be compromised.
Use ultralow-sulfur diesel (ULSD) with 15 ppm sulfur content or less, based on ASTM D2622 test procedure.
Do not use fuel blended with used engine lube oil.
Engine lube oil must have a sulfated ash level less than 1.0 wt %, meeting the API CJ-4 index specifications.
Adequate maintenance of the engine and the diesel particulate filter are the responsibility of the owner/ operator, and are essential to keep the emission levels low. Good operating practices, regular maintenance, and correct adjustments are factors that will help to stay within the regulations.
General Information
See the manufacturer's engine operation manual for specific reccomendations for your engine.
1.
Operate the engine at low load when the engine is first started. After normal oil pressure is reached and the temperature gauge needle begins to move, the engine may be operated at full load.
1.
Electronic engines automatically idle at a slightly higher speed for the correct warm up time after a cold engine start. These electronic engine systems will reduce the idle speed to normal rpm when the engine has warmed sufficiently to operate the vehicle.
2.
Select a gear that allows a smooth, easy start without increasing engine speed above low idle or slipping the clutch. Engage the clutch smoothly. Jerky starts waste fuel and put stress on the drivetrain.
3.
It is seldom necessary to accelerate the engine to governed speed in the lower gears to get the vehicle moving, except in a high-power-demand situation such as starting on a grade. To conserve fuel, start off in low gear, and develop only the engine speed needed to get rolling. Then, increase engine speed gradually as upward gear shifting progresses. This technique will get the vehicle up to the desired cruising speed while minimizing noise emission and maximizing fuel economy. A progressive shift pattern is illustrated in Fig. 7.8 .
3.
Electronic engines can be programmed to limit engine rpm while the vehicle is operated in the lower and higher gears. This feature assists the driver in following "progressive shifting" techniques.
- 1. Governed RPM
- 2. Engine RPM
- 3. Idle RPM
- 4. Miles (kilometers) per Hour
Fig. 7.8, Progressive Shift Pattern
4.
For highway cruising, and for best fuel economy, run the engine at 80 to 90 percent of rated rpm to maintain highway speed. Proper gear selection should permit cruising in the economy range with no appreciable sacrifice in desired highway speed.
4.
It is okay to operate below rated rpm at full throttle if you are satisfied with the way the vehicle performs. However, there are times when hilly terrain, high winds, or other conditions make it impractical to operate without reserve power. Such conditions are better met if the vehicle is operated in a lower gear with reserve power available for changes in terrain, wind, etc.
Driving on Hills
1.
When approaching a hill, open the throttle smoothly to start the upgrade at full power, then shift down as desired, to maintain the optimum vehicle speed.
1.
NOTE: A momentary hesitation in throttle response will occur when a vehicle with a turbocharged engine is started on a grade. Do not disengage the clutch. The rpm will recover, and the vehicle will accelerate up the grade.
2.
On uphill grades, begin downshifting when the engine rpm falls to 1200 rpm. Fuel economy will be best if you let the engine lug back to around this speed before you downshift. Downshift until a gear is reached in which the engine will pull the load. Let the engine lug down if you can make it to the top of a hill without downshifting.
3.
If going up a hill causes a steady decline in engine rpm, downshift as required until the engine can maintain a stable uphill speed. Make full use of each gear before going to a lower gear. By remaining in a gear until arriving at the speed of the next lower gear, the vehicle will top the grade in the best possible time on less fuel and fewer shifts.
4.
The driver can greatly improve driving skill by learning the vehicle's shift points for all gears. By knowing rather than guessing where the shift points are, it is possible to avoid overspeeding the engine when downshifting too soon or missing the full use of a gear by downshifting too late. The shift points of any vehicle can be determined by a simple road-test method. Run the vehicle, and determine the maximum road speed possible in every gear at the engine governed full-load speed setting.
4.
The top road speed possible in a gear would be the shift point for that gear. The results should be recorded in the proper order of shifting and displayed inside the cab.
5.
For improved operating efficiency (fuel economy and engine life), operate in the higher gear at reduced rpm, rather than in the next lower gear at the maximum rpm.
6.
Cruise at partial throttle whenever road conditions and speed requirements permit. This driving technique permits operating within the most economical power range of the engine.
7.
The diesel engine is effective as a brake on downhill grades, but care must be used not to overspeed the engine going downhill. The governor has no control over engine speed when the engine is being turned by the loaded vehicle. A simple rule to follow for engine braking is to select the same gear (or one gear lower) that would be needed to go up the grade.
7.
Never turn off the ignition switch while going downhill.
IMPORTANT: Do not let Caterpillar C–10, C–12, C–15, C–16, and 3406E electronic engines exceed 2300 rpm (2100 rpm if equipped with an exhaust brake).
CAUTION
8.
To slow the vehicle on downgrades and curves (using the engine), shift to a lower gear, and allow the vehicle to decelerate in that gear. The engine provides maximum braking effect when running at the top end of the operating range, but it must not be allowed to exceed its full-load rated rpm.
IMPORTANT: For Mercedes-Benz engines, the maximum speed in regular operation is 2000 rpm. However, during engine braking only, a higher rpm can be used to increase retarding power, if necessary. When using the engine brake it is recommended to use engine speeds up to 2300 rpm. The engine provides maximum braking effect when running at 2500 rpm, but it must not be allowed to exceed this speed.
9.
Continue to downshift as further reduction in vehicle speed is required. If the vehicle is above the allowable maximum speed of a lower gear, use the service brakes to slow the vehicle to an acceptable speed where the transmission may be downshifted safely. Again, the importance of knowing the shift points is demonstrated.
Idling
CAUTION
The common belief that idling a diesel engine causes no engine damage is wrong. Idling produces sulfuric acid, which breaks down the oil and eats into bearings, rings, valve stems, and engine surfaces. If you must idle the engine for cab heat or cooling, the high idle function of the cruise control switches should be used. An idle speed of 900 rpm should be enough to provide cab heat in above 32°F (0°C) ambients.
WARNING
If the engine is programmed with the idle shutdown timer, ninety seconds before the preset shutdown time, the CHECK ENGINE light will begin to flash at a rapid rate. If the position of the clutch pedal or service brake changes during this final ninety seconds (CHECK ENGINE lamp flashing) the idle shutdown timer will be disabled until it is reset.
Cold-Weather Operation—CAT, Cummins, DDE S60, M-B
Satisfactory performance of a diesel engine operating in low ambient temperatures requires modification of the engine, surrounding equipment, operating practices, and maintenance procedures. The lower the temperatures, the greater the amount of modification required; and yet with the modifications applied, the engines must still be capable of operation in warmer climates without extensive changes.
The following information is provided to engine owners, operators, and maintenance personnel on how the modifications can be applied to get satisfactory performance from their diesel engines.
There are three basic objectives:
Reasonable starting characteristics followed by practical and dependable warm-up of the engine and equipment.
A unit or installation that is as independent as possible from external influences.
Modifications that maintain satisfactory operating temperatures with a minimum increase in maintenance of the equipment and accessories.
If satisfactory engine temperature is not maintained, higher maintenance cost will result due to increased engine wear. Special provisions to overcome low temperatures are definitely necessary, whereas a change to a warmer climate normally requires only a minimum of revision. Most of the accessories should be designed in such a way that they can be disconnected so there is little effect on the engine when they are not in use.
IMPORTANT: If a winterfront is used on a vehicle with an electronic engine equipped with a charge air cooler, make sure that there are slit openings distributed across the face of the winterfront to allow airflow through the entire charge-air-cooler core. Do not use a winterfront with closed areas that block uniform air flow across any sections of the charge-air-cooler crossflow tubes. This will adversely affect the operation and durability of the charge air cooler.
On all engines, the following steps are necessary when operating in cold weather:
1.
Check for cracks in the battery cases, for corrosion of the terminals, and for tightness of the cable clamps at the terminals.
2.
Charge the batteries to full capacity. Replace any battery that is unable to hold full charge or is physically damaged.
3.
Check the alternator output.
4.
Check the condition and tension of the drive belts.
Caterpillar
If the engine is in good mechanical condition and the precautions necessary for cold-weather operation are taken, ordinary cold weather will not cause difficulty in starting or loss of efficiency.
If the engine does not start, prime the fuel system.
When the use of unblended No. 2 diesel fuel in winter cannot be avoided, install a thermostatically controlled fuel heater. Fuel heaters can prevent wax from clogging the fuel filters and formation of ice crystals from water in the fuel.
IMPORTANT: If a fuel heater is used, make sure it has thermostatic controls to prevent excessive heating of the fuel in warm weather. Excessive heating of fuel can cause a loss of engine power.
For cold weather operation, use the following guidelines:
1.
When starting the engine in temperatures below 32°F (0°C), use engine lubricants of lower viscosity. Refer to the Caterpillar Operation and Maintenance Manual for specifications.
2.
When the temperature is below freezing, use sufficient antifreeze solution in the cooling system to prevent freezing.
3.
During cold weather, give more attention to the condition of the batteries. Test them frequently to ensure sufficient power for starting. See Group 15 of the Century Class Trucks Workshop Manual for detailed information.
4.
If so equipped, turn off the battery disconnect switch after the engine is shut down, to prevent battery discharge.
4.
For starting below 0°F (–18°C), an optional cold-weather starting assist is recommended. For temperatures below –10°F (–23°C), consult your Caterpillar dealer for recommendations.
5.
When customer parameters include cold-mode operation and the coolant temperature is below 82°F (28°C), the system puts the engine into cold mode. It adjusts the low idle to 600 rpm for the 3406E, C–15, and C–16 engines, and 800 rpm for the C–10 and C–12 engines. It also advances the timing, to reduce white smoke emissions and improve warm-up time. The system will keep the engine in cold mode until the coolant temperature rises above 82°F (28°C). After cold mode has been completed, operate the vehicle at low load and low rpm until the engine coolant reaches normal operating temperature of 189°F (87°C).
6.
Fuel cloud point is the temperature at which wax crystals become visible, which is generally above the pour point of the fuel. To keep the fuel filter elements from plugging with wax crystals, the cloud point should be no higher than the lowest ambient temperature at which the engine must start.
Cummins
The two most commonly used terms associated with preparation of equipment for low-temperature operation are "winterization" and "arctic specifications."
Winterization of the engine and/or components, so that starting and operating are possible in the lowest temperature to be encountered, requires:
Proper lubrication with low-temperature lubricating oils.
Protection from the low-temperature air. The metal temperature does not change, but the rate of heat dissipation is affected.
Fuel of the proper grade for the lowest temperature.
Heat to raise the engine block and component temperatures to at least –25°F (–32°C) for starting in lower temperatures.
Electrical equipment capable of operating in the lowest expected temperature. All switches, connections, and batteries in the electrical system should be inspected and kept in good condition to prevent losses through poor contacts.
Arctic specifications refer to the design of material and specifications of components necessary for satisfactory engine operation in extremely low temperatures to –65°F (–54°C). Contact the nearest Freightliner dealer or Cummins engine dealer, to obtain the special items required.
CAUTION
IMPORTANT: Fuel heaters used on vehicles with Cummins CELECT Plus engine systems could cause high fuel temperatures that affect engine performance and operation of the electronic engine controls. If a fuel heater is used, make sure it has thermostatic controls. If the fuel heater has a timer, set the timer to activate only for a limited period of time before the engine starts. Make sure the fuel heater is used only for starting the engine.
For more information, see the Cummins Operation and Maintenance Manual .
DDE S60
Preparations made in advance of winter and maintenance performed during the cold months will help to ensure efficient engine starting and operation.
Engine oil thickens as it gets colder, slowing cranking speed. When cold, multi-grade oil offers less resistance to the cranking effort of the engine and permits sufficient rpm to be developed to start the engine. See "How to Select Lubricating Oil" in the Detroit Diesel Engine Operator's Guide for specific recommendations.
When an engine equipped with a DDEC system is started at temperatures below 25°F (–4°C), the idle speed automatically increases to 900 rpm. The injection timing is also advanced to decrease white smoke. As the engine oil warms up, the idle speed gradually decreases. When the oil temperature reaches 122°F (50°C), both the idle speed and the injection timing return to normal.
A winterfront may be used to improve cab heating while idling. At least 25% of the grille opening should remain open in sectioned stripes that run perpendicular to the charge air cooler tube flow direction. This assures even cooling across each tube and reduces header-to-tube stress, and possible failure. Winterfronts should only be used when the ambient temperature remains below 10°F (–12°C).
During cold weather, the batteries should be tested more frequently to ensure ample power for starting. All electrical connections should be tight and in good condition to prevent losses through loose or corroded connections.
Ethylene-glycol-base antifreeze is recommended. An inhibitor system is included in this type of antifreeze, and the corrosion protection is sufficient as long as the recommended concentration range of 30 to 67 percent (antifreeze to water by volume) is employed.
If the engine is to be operated in arctic temperatures, consult the nearest Freightliner dealer or an authorized Detroit Diesel engine dealer for information regarding availability of special cold-weather equipment.
Mercedes-Benz
Special precautions must be taken during cold weather. For service products to use in cold weather, see Chapter 5 of the MBE4000 Engine Operator's Manual .
IMPORTANT: At outside temperatures below –4°F(–20°C), a coolant preheater is recommended.
1.
Periodically check the coolant mixing ratio (concentration of antifreeze in the coolant). Add more if necessary. The coolant mixing ratio should never rise above 60 percent antifreeze.
2.
Use low-viscosity lubricating oils for adequate lubrication.
3.
At temperatures below 32°F (0°C), do not use summer-grade (2-D) diesel fuel. To avoid fuel problems due to paraffin separation, use winter-grade (1-D or winterized 2-D) diesel fuel only.
WARNING
4.
When winter-grade diesel fuel is not adequate, it is possible to mix kerosene with the diesel fuel. If it is an EPA07 engine, ultralow-sulphur kerosene must be used. Add the kerosene only when refilling the tank, and before adding the diesel fuel.
NOTE: Engine power may drop according to the proportion of kerosene. For this reason, never add more than 50 percent kerosene to the fuel.
High-Altitude Operation—CAT, Cummins, DDE S60, M-B
Engines lose horsepower when operated at high altitude because the air is too thin to burn as much fuel as at sea level. This loss is about three percent for each 1000 feet (300 m) altitude above sea level for a naturally aspirated engine. Most turbocharged engines are rated for higher altitudes than naturally aspirated engines.
An engine will have smoky exhaust at high altitudes unless a lower gear is used. The engine will not demand full fuel from the fuel system unless the engine is altitude-compensated by the use of a turbocharger. Shift gears as needed to avoid excessive exhaust smoke.
There is no restriction with respect to altitude operation for Mercedes-Benz MBE4000 engines. These engines will perform properly between sea level and 13,000 ft (4000 m) above sea level.
Engine Shutdown—CAT, Cummins, DDE S60, M-B
Caterpillar
CAUTION
1.
With the vehicle stopped, apply the parking brakes. Reduce the engine speed to low idle.
2.
Place the transmission shift lever in neutral.
NOTE: If the engine has been operating at low loads, run it at low idle for 30 seconds before stopping. If the engine has been operating at highway speed or at high loads, run it at low idle for three minutes to reduce and stabilize internal engine temperatures before stopping.
3.
Turn off the ignition switch and shut down the engine.
4.
After engine shutdown, fill the fuel tank.
5.
Check the crankcase oil level. Maintain the oil level between the add and full marks on the dipstick.
6.
If equipped with an idle shutdown timer, it can be set to shut the engine down after a preset amount of time. Ninety seconds before the preset shutdown time, the CHECK ENGINE light will begin to flash at a rapid rate. If the clutch pedal or service brake indicate a position change during this final ninety seconds (diagnostic lamp flashing), the idle shutdown timer will be disabled until reset.
7.
If freezing temperatures are expected, allow the engine jacket water expansion tank to cool, then check the coolant for proper antifreeze protection. The cooling system must be protected against freezing to the lowest expected outside temperature. Add permanent-type antifreeze, if required.
8.
Repair any leaks, perform minor adjustments, tighten loose bolts, etc. Observe the vehicle mileage or the service meter reading, if so equipped. Perform periodic maintenance as instructed in the Maintenance Interval Schedule in the Caterpillar Operation and Maintenance Manual .
Detroit Diesel S60
1.
With the vehicle stopped, apply the parking brakes, and place the transmission in neutral.
2.
Allow the engine to run at idle for four to five minutes. This allows the engine to cool and the turbocharger to slow down.
CAUTION
3.
Turn off the ignition switch and shut down the engine.
Mercedes-Benz
1.
With the vehicle stopped, apply the parking brakes and put the transmission in neutral.
2.
Allow the engine to idle for one to 2 minutes before shutting it down.
3.
Shut down the engine by turning off the ignition.
Engine Braking Systems—CAT, Cummins, DDE S60, M-B
Several types of engine braking systems are optionally available. Each of these systems uses the engine to retard the vehicle on downgrades and reduces the heat load on the service brakes. The engine brakes are meant to be auxiliary vehicle braking systems in addition to the regular service brakes.
Jacobs® Engine Brake
A Jacobs engine brake is a hydraulic-electric engine attachment that converts a diesel engine into an air compressor. This is done by changing engine exhaust valve operation. An engine brake is not a substitute for a service braking system, except in emergencies, because it does not provide the precise control available from the service brakes.
The Jake® Brake is controlled by a single, dash-mounted paddle switch with three positions: OFF, LO, and HI.
Jacobs Engine Brake Operation
WARNING
To engage the engine brake, the dash switch must be in the LO or HI position and both the clutch and throttle pedals must be fully released. To disengage the engine brake, depress the throttle or clutch pedal, or move the dash switch to OFF. Use the LO position when driving on flat, open stretches of road. If you need to use the service brakes to slow down, switch to a higher position until there is no need for the service brakes.
WARNING
Since the engine brake is most effective at rated engine speed, gear selection is very important. Gearing down the vehicle within the limits of the rated engine speed makes the engine brake more effective. Recommended engine braking speed is above 1800 rpm and below the rated speed.
IMPORTANT: Maximum retarder performance is obtained when you use the lowest possible gear without exceeding the recommended engine braking speed.
"Control speed" is the speed at which the engine brake performs 100 percent of the required downhill braking, resulting in a constant speed of descent. The control speed varies, depending on vehicle weight and the downhill grade.
Below a set engine speed (set at the factory to 700 rpm), the engine control unit (ECU) will not engage the engine brake. The engine brake will not work below the set engine speed.
For faster descent, select a higher gear than that used for control speed. Service brakes must then be used intermittently to prevent engine overspeed and to maintain desired vehicle speed.
IMPORTANT: When descending a grade, remember that frequent use of service brakes causes them to become hot, which results in a reduction of their stopping ability. Grade descent speed should be such that the service brakes are used infrequently and that they remain cool, thus retaining their effectiveness.
A driver may descend slower than control speed by selecting a lower gear, one that will not overspeed the engine. The engine brake retarding force will then be sufficient to cause vehicle deceleration. Occasional deactivation of the engine brake may be necessary to maintain the designated road speed under these conditions.
WARNING
Whenever vehicle braking is required, the engine brake may be used with the service brakes. There is no time limit for operation of the engine brake.
1.
After the engine is warmed up and the vehicle is in motion, move the paddle switch to the desired position, LO or HI. Depending on the engine model, LO will provide 1/3 or 1/2 of the full braking capacity of the engine. HI will provide maximum engine braking.
2.
The engine brake activates when the dash switch is in LO or HI position and the driver's feet are removed from both the clutch and throttle pedals. If it fails to activate, take the vehicle to an authorized Freightliner dealer for service.
3.
To obtain maximum retarding, maintain the top governed speed of the engine through appropriate selection of gears when the engine brake is in use.
CAUTION
4.
When either the clutch or throttle pedal is depressed, the engine brake is deactivated.
BrakeSaver
The BrakeSaver (optional on 3406E engines) permits the operator to control the speed reduction of the vehicle on grades, curves, or anytime speed reduction is necessary but long applications of the service brakes are not desired.
During downhill operation, the crankshaft is turned by the rear wheels (through the drivetrain). To reduce the speed of the vehicle, an application of braking force can be made to the crankshaft. The BrakeSaver does this by converting rotation energy into heat, which is removed by the engine cooling system. The BrakeSaver is controlled by the driver, as necessary, by operating a lever on the instrument panel. Braking force increases as the lever is moved toward the ON position. An air pressure gauge provides a relative indication of the braking force. An oil temperature gauge indicates the heat in the BrakeSaver during its operation. If the temperature gauge indicates HOT, the BrakeSaver control lever must be moved to the OFF position. The oil temperature will decrease rapidly with the BrakeSaver off. When the temperature reaches normal, the BrakeSaver can be used.
CAUTION
Turbo Brake (MBE4000 only)
For high braking output, the Mercedes-Benz MBE4000 engine can be equipped with an optional turbo brake.
The turbo brake can be operated either manually or automatically, through the cruise control function. If the turbo brake is operated manually, there is a four-position switch on the dashboard: OFF/ LOW/ MED/ HIGH.
The turbo brake provides 600 brake horsepower at 2500 engine rpm. In the braking condition, the MBE4000 turbo brake engine operates as a turbocharged compressor, resulting in high braking output. It is recommended to operate the turbo brake up to the 2300 rpm level. This provides approximately 550 brake horsepower which should cover most situations. If additional braking power is required, engine speed can be increased to 2500 rpm maximum, resulting in 600 brake horsepower.
CAUTION
Because the charge air pressure is maintained at a high level during braking, full throttle response is available immediately, if the operator desires it, without any turbo lag.
CAUTION
The MBE4000 turbo brake is combined with Mercedes-Benz constant throttle technology, but an exhaust flap is not used. The turbo brake emits very low levels of noise, making it an environmentally friendly system. It is maintenance-free, highly reliable, and adds virtually no weight to the engine.
Constant-Throttle Engine Brake (MBE4000 only)
The standard engine braking system is the constant-throttle system combined with an exhaust flap. To increase braking performance, each cylinder is equipped with a small valve built into the cylinder head. This valve is always open during engine brake activation, and it allows compressed air to exhaust when the piston is at top dead center. This removes pressure from the piston as it moves to the bottom dead center position.
The standard constant-throttle engine brake is equipped with an exhaust flap. During engine brake operation, the six constant throttle valves are open in parallel and the exhaust flap is closed. For normal engine brake use, operate the engine up to 2300 rpm. If increased retarding power is required, the maximum 2500 engine rpm can be used.
CAUTION
A two-position switch on the dash controls the engine braking system. Like the exhaust flap, the constant throttles are deactivated when the accelerator or clutch pedal is depressed. The ABS system, when active, also deactivates constant-throttle braking.
Exhaust Brake System—CAT, Cummins, DDE S60, M-B
General Information
An exhaust brake is an optional auxiliary braking system that assists but does not replace the service brake system. The exhaust brake can be used alone or together with the constant-throttle valves for steep or long grades. It cannot be used at the same time as a Jake® brake.
When only the exhaust brake is installed, a two-position switch on the dash controls the engine braking system. The exhaust brake is only active when the engine speed is between 900 and 2500 rpm. Depressing the accelerator or clutch pedal deactivates the exhaust brake. The ABS system, when active, also deactivates the exhaust brake.
The exhaust brake switch located on the control panel, in combination with the accelerator and clutch pedals, allows the driver to make maximum use of the exhaust brake in off-highway and mountain driving as well as in traffic or high-speed highway driving.
The exhaust brake is a butterfly valve mounted in the exhaust pipe. When the driver's foot is not on the accelerator pedal and the exhaust brake switch is in the on position, an air cylinder shuts the butterfly valve, which restricts the flow of exhaust gases and retards the engine. This retarding action is carried through the engine and drivetrain, slowing the vehicle and reducing the need for frequent service brake applications.
Exhaust brakes are not intended for use as the primary braking system during vehicle operation.
Starting the Engine
Before starting the engine, make sure that the exhaust brake switch is in the off position. Do not turn the exhaust brake on until the engine has reached normal operating temperatures.
Driving Downhill
While approaching a steep grade, make sure that the exhaust brake switch is in the on position. The exhaust brake comes on as soon as you remove your foot from the accelerator pedal. While going down the grade, use a low enough gear to safely descend with a minimum application of the service brakes. As a general guideline, use the same gear as you would to ascend the hill.
CAUTION
Apply the service brakes to reduce the engine rpm or make a slower descent by using a lower gear.
WARNING
Exhaust Brake Operating Characteristics
When you remove your feet from both the accelerator and clutch pedals and the exhaust brake switch is in the on position, the exhaust brake is applied. The following conditions should exist if the brake is operating properly.
A slight change in the sound of the engine may be noticed when the exhaust brake is applied.
Exhaust smoke should appear normal.
Engine temperature should remain in the normal operating range.
Road speed usually decreases when the exhaust brake is applied during a descent. When the vehicle is carrying a heavy load or the grade is extremely steep, you may need to apply the service brakes occasionally.
Do not expect a retarding effect similar to sudden hard application of the service brakes. The exhaust brake retards the vehicle with a smooth braking effect.
During a descent, the tachometer usually shows a drop in rpm depending on the grade and the vehicle load.
Depending on the grade and vehicle load, you may or may not feel the retarding force acting against your body when the brake is applied. The retarding force of the brake may not always be noticed, but it is actually preventing the vehicle from going much faster.
Make sure the exhaust brake is turned off before shutting off the engine.
Clutches
General Information
Clutches are designed to absorb and dissipate more heat than encountered in typical operation. The temperatures developed in typical operation will not break down the clutch friction surfaces. However, if a clutch is slipped excessively, or asked to do the job of a fluid coupling, high temperatures develop quickly and destroy the clutch. Temperatures generated between the flywheel, driven discs, and pressure plates can be high enough to cause the metal to flow and the friction facing material to char and burn.
Heat and wear are practically nonexistent when a clutch is fully engaged. But during the moment of engagement, when the clutch is picking up the load, it generates considerable heat. An improperly adjusted or slipping clutch will rapidly generate sufficient heat to destroy itself.
To ensure long service life of the clutch; start in the right gear, be alert to clutch malfunctions, and know when to adjust the clutch.
Clutch Operation
Clutch Break-In
With a new or newly installed clutch, the clutch may slip for a short time while the friction surfaces break-in. However, allowing the clutch to slip for more than two seconds can severely damage the clutch disc, pressure plate, and the flywheel.
During initial operation of a new vehicle or a vehicle with a new clutch, check for clutch slippage during acceleration. If the clutch slips, decelerate until the clutch does not slip. Allow the clutch to cool 15 to 30 seconds, and then gradually accelerate again. If the clutch continues to slip, repeat the procedure. If necessary, repeat the procedure up to five times. If the clutch slips after five attempts, stop the vehicle. Allow the clutch to cool for at least one hour. Notify your Freightliner dealer of the problem.
CAUTION
Moving the Vehicle in the Proper Gear
An empty truck can be started in a higher transmission gear than can a partially or fully loaded truck. A good rule of thumb for the driver to follow is to select the gear combination that allows the vehicle to start moving with an idling engine, or, if necessary, just enough throttle to prevent stalling the engine. After the clutch is fully engaged, the engine can be accelerated to the correct rpm for the upshift into the next higher gear.
Gear Shifting Techniques
Shift into the next higher gear when the vehicle speed allows the transmission input shaft speed to match the flywheel speed when engaging the clutch. This technique results in the smallest speed difference between the clutch disc and the flywheel and causes the least heat and wear on the clutch assembly. When downshifting, the input shaft speed must be increased by slightly revving the engine to match the flywheel speed for smooth clutch engagement. For transmission operating instructions, refer to Chapter 8 in this manual.
Vehicle Loading
Clutches are designed for specific vehicle applications and loads. These weight limitations should not be exceeded.
CAUTION
Using the Clutch
The clutch pedal must be used only to start the vehicle moving or while shifting. To start the vehicle moving, depress the clutch pedal all the way to the floor plate (see "Using the Clutch Brake") and shift from neutral to a low gear. Slowly raise your foot until the clutch starts to engage. In this position the clutch is starting to connect the transmission input shaft to the flywheel and is causing the most heat and wear. Slightly increase the engine speed and smoothly allow the clutch pedal to return to its at-rest position. Do not allow the clutch to remain in the partially engaged position any longer than necessary to obtain a smooth start.
To shift gears while the vehicle is moving, push the clutch pedal most of the way (but not all of the way) to the floor plate. Shift the transmission into neutral and fully release the clutch pedal. If upshifting, wait long enough for the engine speed to decrease to the road speed. If downshifting, increase the engine speed to match the road speed. Again, push down the clutch pedal part way and then move the shift lever to the next gear position. Fully release the clutch pedal after completing the shift.
Slightly depressing the clutch pedal while driving is damaging to the clutch, because partial clutch engagement causes slippage and heat. Resting your foot on the clutch pedal will also put a constant thrust load on the release bearing, thinning the bearing lubricant and increasing the wear on the bearing.
Using the Clutch Brake
The clutch brake is applied by depressing the clutch pedal past the fully released clutch position, almost to the floor plate. The last part of the clutch pedal travel will compress the clutch brake plates together, stopping the transmission input shaft. The purpose of the clutch brake is to stop the transmission gears from rotating in order to quickly engage a transmission gear after idling in neutral.
CAUTION
Holding the Vehicle on an Incline
Always use the vehicle service brakes to prevent the vehicle from rolling backwards while stopped on a hill. Slipping the clutch on a hill to maintain the vehicle position will quickly damage the clutch assembly.
Coasting
Coasting with the clutch pedal depressed and the transmission in a low gear can cause high driven disc speed. The clutch speed can be much higher under these conditions than when the engine is driving the clutch. This condition creates a hazardous situation due to the lack of vehicle control and due to the high clutch disc speed. Engaging the clutch under these conditions can cause component damage because of the shock loads to the clutch and drivetrain.
WARNING
Clutch Maintenance
Checking the Clutch Adjustment
Reporting erratic clutch operation as soon as possible gives maintenance personnel a chance to inspect, lubricate, and adjust the clutch components. The driver can be aware of clutch wear by noticing the gradual decrease in the distance the clutch pedal moves before resistance is felt. A correctly adjusted clutch must have about 3/4 inch (19 mm) of travel at the top of its stroke before a stronger resistance can be felt. See Fig. 7.9 . If the free pedal travel is less than this distance, have the clutch adjusted.
- A. Free Pedal
Fig. 7.9, Clutch Free Pedal Travel
The clutch pedal free travel should be checked and commented on daily in the driver's report.
See Group 25 of the Columbia® Workshop Manual for clutch adjustment procedures and specifications.
CAUTION
Checking the Clutch Brake Operation
Clutch brake operation can be felt as an increased resistance as the clutch pedal approaches the bottom of its stroke. If the gears grind when shifting into first or reverse gear from neutral with the clutch pedal fully depressed, the clutch pedal is out of adjustment or the clutch brake is worn and needs to be replaced.
Adjusting the Clutch
Clutches have an internal adjustment and external linkage adjustment. See Group 25 of the Columbia® Workshop Manual for clutch adjustment procedures and specifications.
CAUTION
Lubricating the Clutch Linkage and Bearing
On vehicles equipped with a greaseable release bearing, the release bearing and linkage should be lubricated at frequent intervals. See Group 25 of the Columbia®Maintenance Manual for intervals and procedures.
CAUTION