Clutch
Clutch General Information
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.
Typical operation will not break down the clutch friction surfaces. Heat and wear are almost nonexistent when a clutch is fully engaged. However, during the moment of engagement, when the clutch is picking up the load, considerable heat is generated. If a clutch slips excessively, high temperatures develop quickly between the flywheel, driven discs, and pressure plates. An improperly adjusted or slipping clutch can generate temperatures high enough to destroy the clutch.
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.
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 Western Star dealer of the problem.
Moving the Vehicle in the Proper Gear
An empty vehicle can be started in a higher 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.
Gear Shifting Techniques
Upshift into a higher gear only 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.
Vehicle Loading
Clutches are designed for specific vehicle applications and loads.
Clutch Brake
Apply the clutch brake by depressing the clutch pedal all the way to the floor plate. The last part of 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.
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 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 for the engine speed to decrease to the road speed. When downshifting, increase the engine speed to match the road speed. Fully release the clutch pedal after completing the shift.
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.
Warning: 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.
Clutch Maintenance
Checking the Clutch Adjustment
Report erratic clutch operation as soon as possible to give maintenance personnel a chance to inspect, lubricate, and adjust the clutch components. Notice any gradual decrease in the distance the clutch pedal moves before resistance is felt.
Notice: Operating the vehicle with incorrect free pedal could result in clutch damage.
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. . If the free pedal travel is less than this distance, have the clutch adjusted.
Check the clutch free pedal travel daily and note it in the driver's report.
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Free Pedal
Fig. 1, Clutch Free Pedal Travel
Adjusting the Clutch
Clutches have an internal adjustment and external linkage adjustment.
Notice: Operating the vehicle with the clutch improperly adjusted could result in clutch or clutch brake failure.
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.
Lubricating the Clutch Release Bearing
Notice: Failure to lubricate the release bearing and linkage as recommended could result in release bearing and clutch damage.
On vehicles equipped with a greaseable release bearing, the release bearing should be lubricated at regular intervals. See the Western Star Maintenance Manual for intervals and procedures.