2. Push the clutch pedal only until all free play is
removed. This causes contact with the release levers
or fingers, allowing the throwout bearing to rotate
without disengaging the clutch. If you hear a noise in
this position, typically a whirring or grinding sound,
the throwout bearing is probably defective.
3. Push the clutch pedal to the floor. If a noise—typically,
a squealing or howling sound—occurs on disengage-
ment, the pilot bearing is probably defective.
Sometimes, the clutch assembly will have a rattle,
especially when the clutch is fully engaged and there is
no foot pressure acting on the linkage. A possible source
of the rattle is a clutch fork that is loose on its pivot ball.
The rattle may be caused by too much clearance
between the fork and the groove in the throwout bear-
ing. A loose fit between parts of a rod-and-lever linkage
or a missing tension spring can cause the mechanism to
rattle. It may be possible to tighten the clutch fork retainer
clips or springs to reduce clearances and quiet the
linkage.
Rattles can also be caused by weak pressure plate
retracting springs in the diaphragm-spring pressure plate
assembly, or by weak or broken clutch disc cushion
springs. Rattles stemming from these problems are usually
loudest when the clutch is disengaged.
Loose flywheel attaching bolts cause movement at the
mounting surfaces of the crankshaft and flywheel. This
movement causes a deep knocking noise that is often
mistaken for an engine main bearing or rod bearing knock.
The noise may be accompanied by vibration. It can usually
be reduced by disengaging the clutch. Pressure from the
throwout bearing, acting through the release levers or
fingers and the clutch cover, press the flywheel tightly
against the crankshaft, quieting the knock.
Hard Pedal Effort
Hard pedal effort is noticed when the clutch pedal is
excessively hard to push down. If the pedal is hard to
depress, the problem is usually in the linkage. If the driver
is strong enough to depress the pedal, it may stay on the
floor or rise very slowly when released. Components may
wear quickly.
To isolate the cause of the problem, disconnect the
clutch linkage at the clutch fork and try to move the pedal
by hand. If the clutch pedal does not move easily, the
problem is somewhere in the linkage.
Where rod-and-lever linkages are concerned, hard
pedal effort is due to lack of lubrication or to some part of the
linkage that is bent or loose enough to jam. Sometimes, a
rock or other material gets thrown up and jams the linkage.
Clutch pedals of cable linkages usually are hard to
depress because moisture has entered the cable sheath.
Moisture washes out the cable lubricant and causes corro-
sion. It is also possible that the cable was misrouted during
installation and needs rerouting. If the cable is kinked as a
result of misrouting, it should be replaced.
Clutch pedals of hydraulic linkages are hard to
depress because of master cylinder or slave cylinder
problems. The piston sometimes sticks due to internal
corrosion. The usual cause, however, is swollen piston
seals. This problem is a result of using a petroleum-based
oil, such as automatic transmission fluid, instead of brake
fluid (DOT 3 or DOT 4) to refill the reservoir. Petroleum-
based oils will cause the seals to swell, jamming the piston
in the cylinder. When this occurs, the seals must be
replaced.
A less common cause of hard pedal effort in a
hydraulic system is a swollen hydraulic hose. If the hose
swells so that the fluid passageway becomes fairly
constricted, it will take longer to actuate the slave cylinder
piston. The swollen hose will slow clutch disengagement.
It will also slow clutch reengagement and pedal return.
If the clutch linkage worked as it should when it was
disconnected—that is, if it moved easily—the problem is
in the clutch assembly. The two most common causes are
a throwout bearing collar that is sticking on its hub or bind-
ing in the clutch fork. This usually occurs after the vehicle
has been operated in deep water, causing water to enter
the clutch housing and wash off the lubricant.
Chapter 7 Clutch Problems, Troubleshooting, and Service 131
Worn
pilot
bearing
Transmission
input shaft
Worn
transmission
front bearing
Dry
throwout
bearing
Figure 7-4. Three bearings associated with the clutch are the
pilot bearing, the throwout bearing, and the transmission front
bearing. Each can be detected as a source of noise by operating
the clutch pedal. Wear or lack of lubrication can cause the
bearings to make noise. (Luk)