Clutch Operation
Clutch Break-In
The clutch may slip for a short time while the friction surfaces break-in on a new or newly-installed clutch. However, allowing the clutch to slip for more than two seconds can severely damage the clutch disc, pressure plate, and the flywheel.
Notice: Do not allow sustained slippage of the clutch; which will severely damage the clutch disc, pressure plate, or flywheel. Damage caused by clutch slippage due to improper break-in is not warrantable.
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, then gradually accelerate again. If the clutch continues to slip, repeat the procedure as many as five times. If the clutch slips after five attempts, stop the vehicle and allow the clutch to cool for at least one hour. Notify your Freightliner dealer of the problem.
Moving the Vehicle in the Proper Gear
An empty vehicle can be started in a higher transmission gear than can a partially- or fully-loaded vehicle. 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 a higher gear.
Gear Shifting Techniques
Upshift into a 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, increase the input shaft speed to match the flywheel by slightly revving the engine. For transmission operating instructions, refer to the transmission headings in this chapter.
Vehicle Loading
Clutches are designed for specific vehicle applications and loads. Do not exceed these weight limitations.
Notice: Exceeding vehicle load limits can result in damage to the clutch and the entire powertrain.
Clutch Brake
Apply the clutch brake by depressing the clutch pedal all the way 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 clutch brake stops the transmission gears from rotating in order to quickly engage a transmission gear after idling in neutral.
Notice: Never apply the clutch brake when the vehicle is moving. If the clutch brake is applied when the vehicle is moving, the clutch brake will try to stop or decelerate the vehicle, causing rapid wear of the clutch brake friction discs. Considerable heat will be generated, causing damage to the release bearings and the transmission front bearings.
Using the Clutch
Use the clutch pedal only when starting the engine, launching the vehicle from a stop, or shifting. To launch a stationary vehicle, depress the clutch pedal all the way to the floor plate (see "Using the Clutch Brake" above) 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 the rest position. Do not allow the clutch to remain in the partially-engaged position any longer than necessary to obtain a smooth start.
Double-clutch to shift gears while the vehicle is moving. Depress the clutch pedal most of the way in, but not all the way to the floor plate. Depressing the clutch pedal to the floor plate will engage the clutch brake. Shift the transmission into neutral and fully release the clutch pedal. When upshifting, wait long enough for the engine speed to decrease to the road speed. When downshifting, increase the engine speed to match the road speed. Again, depress 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.
Notice: Riding the clutch 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.
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 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.
Note: Always shift into the gear that is correct for the traveling speed of the vehicle and engage the clutch. Coasting with the clutch disengaged can prevent engagement of the correct transmission gear which can cause loss of vehicle control, possibly resulting in personal injury or property damage.
High clutch disc speeds while coasting can also cause the clutch facing to be thrown off the disc. Flying debris from the clutch can cause injury to persons in the cab.