To maintain clutches, follow the installation guidelines/procedures provided by the component supplier. Replace any worn components that may affect clutch performance. And, follow the safety warnings.
General shop practices include:
Cleaning. Use a vacuum to remove lining dust from the flywheel, clutch or other areas. Do not use compressed air because the dust will be spread to other areas.
Flywheel. Follow the engine manufacturer's recommendations/guidelines on machining. When using a 15.5-inch clutch, ensure that the flywheel hub opening will accept the damper assembly without interference. There are three different 15.5-inch flywheels used today. They have hub bore openings of 7 inches, 8.5 inches and 10 inches in diameter. Do not use an organic facing with a 10-inch flywheel hub diameter. The facing will extend into the bore opening and will not have full contact.
Facing material. Do not replace ceramic facings with organic facings. Always replace like for like.
Damper. Replace soft-rate damped clutches (low spring rate) with soft rate-damped clutches. Do not use non-soft-rate-type discs in soft rate-type applications.
Tools. For safety and efficiency, use the proper tools. A 15½-inch clutch assembly (2 discs, center plate and cover assembly) weighs approximately 136 pounds to 149 pounds. Always use a clutch installation jack. If the cover is dropped or damaged, do not install it until the components can be inspected. If the damaged clutch assembly is installed, it can cause further serious damage. Do not strike a clutch with a hammer under any circumstances.
Ensure that an appropriate transmission jack is used when removing or installing the transmission.
The transmission jack needs to be properly adjusted and securely attached to the transmission. Do not allow the transmission to hang by the input shaft during installation or removal. Damage to the input bearing or the clutch can result. When the installation is complete, check to see that nothing interferes with or touches the linkage. Also, be sure that all hoses and wires are secured.
Driving techniques. Drivers always should use the brakes, instead of the clutch and gas pedals, to stop a vehicle on an incline. Using the clutch and gas pedals to balance on a hill generates heat, increases wear and causes the brake lights to be off. And, coasting down inclines with the clutch depressed can result in clutch disc speeds that can damage the clutch.
The clutch release system, which includes the release bearing and sleeve bushing, cross-shaft bushings and all the release linkage, should be lubricated monthly or per the vehicle builder's recommendation. Consider the linkage from the cross-shaft all the way back to the pedal. Follow the OEM's recommendations for the lubricant to be used on the linkage and cross-shafts.
The release bearing and sleeve require the use of a high-temperature, lithium-based, multi-purpose wheel bearing grease (NLGI #3 or equivalent). If a non-high-temperature grease is used, release bearing life will be shortened. This has become more important as chassis component temperatures have risen with higher-horsepower, aerodynamic vehicles.
To properly lubricate the release bearing, apply grease to the fitting until a small amount of grease is coming out of the bearing housing. Apply grease to release yoke tips where they contact the bearing housing and the transmission input bearing retainer to lubricate the release sleeve bushing. If the release bearing is equipped with a lube tube, be sure that grease can be seen coming out of the bearing housing. This ensures that grease is reaching the bearing. Be sure that the lube tube is secure and is not damaged.
Extended-maintenance clutches also should use this procedure.
Maximizing Clutch Life
Meritor Automotive, Troy, Mich., says that clutch life can be maximized with maintenance procedures and regular clutch adjustments. Most common heavy-duty trucks use manually adjustable clutches, but self-adjusting clutches also are available.
With mandatory clutch adjustment, select a mileage suitable to your operation and perform internal clutch adjustments at those intervals. Use technical and reference material from the clutch supplier. Make sure you understand the components and use correct tools and procedures when making clutch and linkage adjustments.
Drivers also should be notified of recurring problems. For example, a recurring dragging complaint may indicate an installation problem.
Bob Deierlein is Waste Age's truck editor.