Check and attempt to adjust the clutch pedal play before
attempting to diagnose any clutch problems. If the friction lining of
the clutch is worn too thin, the clutch cannot be adjusted successfully.
The most common clutch problems are described here.
Clutch slippage is a condition in which the engine
overspeeds without generating any increase in torque to the driving
wheels. It occurs when the clutch disc is not gripped firmly between the
flywheel and the pressure plate. Instead, the clutch disc slips between
these driving members. Slippage can occur during initial acceleration or
subsequent shifts, but it is usually most noticeable in higher gears.
One way to check for slippage is by driving the vehicle.
Normal acceleration from a stop and several gear changes indicate
whether the clutch is slipping.
Slippage also can be checked in the stop. Check the
service manual for correct procedures. A general procedure for checking
clutch slippage follows. Be sure to follow the safety precautions stated
With the parking brake on, disengage the clutch. Shift
the transmission into third gear, and increase the engine speed to about
2000rpm. Slowly release the clutch pedal until the clutch engages. The
engine should stall immediately.
If it does not stall within a few seconds, the clutch is
slipping. Safety raise the vehicle and check the linkage for binding and
broken or bent parts. If no linkage problems are found, the transmission
and the clutch assembly must be removed so the clutch parts can be
Clutch slippage can be caused by an oil-soaked or worn
disc facing, warped pressure plate, weak diaphragm spring, or the
release bearing contacting and applying pressure to the release levers.
Drag and Binding
If the clutch disc is not completely released when the
clutch pedal is fully depressed, clutch drag occurs. Clutch drag causes
gear clash, especially when shifting into reverse. It can also cause
hard starting because the engine attempts to turn the transmission input
To check for clutch drag, start the engine, depress the
clutch pedal completely, and shift the transmission into first gear. Do
not release the clutch. Then, shift the transmission into neutral and
wait 5 seconds before attempting to shift smoothly into reverse.
It should take no more than 5 seconds for the clutch
disc, input shaft, and transmission gears to come to a complete stop
after disengagement. This period, called the clutch spindown time, is
normal and should not be mistaken for clutch drag.
If the shift into reverse causes gear clash, raise the
vehicle safely and check the clutch linkage for binding, broken, or bent
parts. If no problems are found in the linkage, the transmission and
clutch assembly must be removed so that the clutch parts can be
Clutch drag can occur as a result of a warped disc or
pressure plate, a loose disc facing, a defective release lever, or
incorrect clutch pedal adjustment that results in excessive pedal play.
Biding can result when the splines in the clutch disc
hub or on the transmission input shaft are damaged or when there are
problems with the release levers.
A shaking or shuddering that is felt in the vehicle as
the clutch is engaged is known as clutch chatter. It usually occurs when
pressure plate first contacts the clutch disc and stops when the clutch
is fully engaged.
To check for clutch chatter, start the engine, depress
the clutch completely, and shift the transmission into first gear.
Increase engine speed to about 1500rpm, then slowly release the clutch
pedal and check for chatter as the pedal begins to engage. Do not
release the pedal completely, or the vehicle might jump and cause
serious injury. As soon as the clutch is partially engaged, depress the
clutch pedal immediately and reduce engine speed to prevent damage to
the clutch parts.
Usually clutch chatter is caused by liquid leaking onto
the clutch and contaminating its friction surfaces. This results in a
mirror-like shine on the pressure plate or a glazed clutch facing. Oil
and clutch hydraulic fluid leaks can occur at the engine rear main
bearing seal transmission input shaft seal, clutch slave cylinder, and
hydraulic line. Other causes of clutch chatter include broken engine
mounts, loose bell housing bolts, and damaged clutch linkage.
During disassembly, check for a warped pressure plate or
flywheel, hot spots on the flywheel, a burned or glazed disc facing, and
worn input shaft spline. If the chattering is caused by an oil-soaked
clutch disc and no other parts are damaged, then the disc alone needs to
be replaced. However, the cause of the oil leak must also be found and
Pedal pulsation is a rapid up-and-down movement of the
clutch pedal as the clutch disengages or engages. This pedal movement
usually is minor, but it can be felt through the clutch pedal. It is not
accompanied by any noise. Pulsation begins when the release bearing
makes contact with the release levers.
To check for pedal pulsation, start the engine, depress
the clutch pedal slowly until the clutch just begins to disengage, and
then stop briefly. Resume depressing the clutch pedal slowly until the
pedal is depressed to a full stop.
On many vehicles, minor pulsation is considered normal.
If pulsation is excessive, the clutch must be removed and disassembled
Pedal pulsation can result from the misalignment of
parts. Check for a misaligned bell housing or a bent flywheel. Inspect
the clutch disc and pressure plate for warpage. Broken, bent, or warped
release levers also create misalignment.
Clutch vibrations, unlike pedal pulsations, can be felt
throughout the vehicle, and they occur at any clutch pedal position.
These vibrations usually occur at normal engine operating speeds (more
than 1500 rpm).
There are several possible sources of vibration that
should be checked before disassembling the clutch to inspect it. Check
the engine mounts and the crankshaft damper pulley. Look for any
indication that engine parts are rubbing against the body or frame.
Accessories can also be a source of vibration. To check
them, remove the drive belts one at a time. Set the transmission in
neutral, and securely set the emergency brake. Start the engine and
check for vibrations. Do not run the engine for more than 1 minute with
the belts removed.
If the source of vibration is not discovered through
these checks, the clutch parts should be examined. Be sure to check for
loose flywheel bolts, excessive flywheel runout, and pressure plate
cover balance problems.
Many clutch noises come from bushings and bearings.
Pilot bushing noises are squealing, howling, or trumpeting sounds that
are most noticeable in cold weather. These bushing noises usually occur
when the pedal is being depressed and the transmission is in neutral.
Release bearing noise is a whirring, grating, or grinding sound that
occurs when the clutch pedal is depressed and stops when the pedal is
fully released. It is most noticeable when the transmission is in
neutral, but it also can be heard when the transmission is in gear.