Clutch maintenance, like brake maintenance, helps your customer receive the maximum service life from his clutch components. You can't control how he uses his clutch (or his brakes), but you can make certain the clutch system is properly adjusted and working as the manufacturer intended.

Begin with the clutch linkage adjustment. Some vehicles have hydraulic clutch master and slave cylinders, which require no periodic adjustment after initial installation. Other cable-operated systems have a self-adjusting mechanism built into the clutch pedal mechanism to eliminate the need for periodic adjustment. But the majority of cable-operated clutch systems do require periodic adjustment.

As the clutch disk wears, the pressure plate fingers rise and free play between the fingers and the clutch release bearing is reduced. Hydraulic systems compensate for this change automatically; most cable-operated systems do not. If the cable is not adjusted to compensate for the reduced free play, the clutch release bearing will remain in constant contact with the pressure plate fingers. This can lead to premature release bearing failure and/or noise. In extreme cases, an incorrectly adjusted clutch cable (no free play) will keep the pressure plate from firmly gripping the clutch disk. The clutch will slip under load, causing accelerated wear and eventual failure. All of these problems can be avoided, or at least postponed, if the clutch cable receives periodic inspections and adjustments as necessary. Consult your service information sources for the clutch free play specifications for the vehicle you're servicing.

Clutch cables also may stretch, increasing free play beyond specification. In a perfect situation, the clutch cable would stretch at the same rate at which the clutch disk wears, maintaining free play at a consistent measurement. This rarely occurs, however. More commonly, the stretched cable results in excessive free play. The clutch pedal must move several inches before it begins to disengage the pressure plate. The pedal may run out of travel before the pressure plate completely releases its grip on the clutch disk. This causes difficulty shifting, clashing gears and a vehicle that creeps slowly forward even when the clutch pedal is on the floor. It also may be difficult to make a smooth start because the clutch will begin to engage as soon as the pedal leaves the floor. In a worst-case scenario, the clutch may never completely disengage.
Advertisement

Inspect the cable free play and adjust it as necessary. If the adjustment is near the end of its travel, an abnormally stretched cable may be indicated; replace it as necessary. On hydraulic clutch systems, a clutch with the symptoms described above may indicate a failed component, air in the system or a hydraulic fluid leak. Anything that keeps the full leverage supplied by the clutch pedal from reaching the clutch control fork will cause engagement/disengagement problems.

Check the clutch master cylinder fluid level. Under normal conditions, the level should remain relatively constant throughout tire clutch components' service life. If the level is abnormally low, start looking for leaks. Leaks at the slave cylinder should be relatively easy to spot if the slave cylinder is out in the open on the transmission. The same goes for the single hydraulic line running between the master and slave cylinders. Trace its path and check for moist areas. Spotting leaks at the master cylinder may be a bit trickier, as its open cylinder end extends into the passenger compartment. A few drops of brake fluid caused by a failed seal may be easily absorbed by the carpet and insulation under the dash. If your customer complains about unusual smells inside the car, you're on to something.

During regular vehicle maintenance, be on the lookout for other fluid leaks that may find their way into the clutch housing. Any fluid that's allowed to reach the clutch disk and pressure plate will damage the parts and prevent proper clutch operation.

Hydraulic clutch systems, like hydraulic brake systems, require one type of maintenance service not shared by cable-operated systems: periodic fluid replacement. Hydraulic clutch systems use brake fluid, and brake fluid naturally absorbs moisture over time. Moisture damages hydraulic components and shortens their service life. Periodic fluid flushing removes the moisture and will help the hydraulic components last at least as long as the clutch disk, pressure plate and release bearing.

Making a vehicle's clutch components deliver as many miles as possible is a skill not all drivers master. Just its some of your customers seem to bum through their brake linings at a record pace, others will wear out their clutches much faster than more careful drivers. With your help, at least some of your customers may be able to make their original clutch components last the entire period of vehicle ownership.