you, the technician, to find out what caused the prema-
ture clutch damage, so the problem might be prevented in
the future.
As stated, clutch problems can occur as a result of
careless operation. Driving with a foot resting on the
clutch pedal is an example. This careless habit, called
riding the clutch, causes the clutch to slip. As a result,
excess heat is generated and premature wearing of clutch
friction surfaces occurs. Among the different ways clutches
are misused, riding the clutch is the most common. It can
put the equivalent of 50,000 miles of normal wear on a
clutch in under 10,000 miles.
Naturally, clutch problems can occur as a result of
abuse. An example is increasing engine speed and then
suddenly releasing the clutch pedal, allowing the pressure
plate apply springs to engage the clutch almost instantly.
This is often referred to as dumping the clutch, or popping
the clutch. It causes instant heat buildup in the clutch disc
facings and places tremendous stress on the clutch and the
entire drive train.
Clutches usually do not last very long under this
type of abuse. Overheated clutch facings, a result of
dumping the clutch, can become glazed within seconds.
This form of abuse can also cause flywheel, clutch cover,
or clutch housing attaching bolts to shear off. Further, it
can cause clutch disc hub splines to be stripped or input
shafts to break.
Placing more load on a clutch than it is designed to
handle can also be a source of damage. An example is
starting off in high, rather than in low, gear. Shifting into a
higher gear before the engine has reached the proper rpm
also overloads the clutch, as does attempting to change
gears at very high engine speeds. Another example is over-
loading the vehicle to the point that the clutch must be
allowed to slip heavily when starting off, just to get the
vehicle moving. This is a common problem on vehicles
used for towing.
As stated, outside factors can also cause clutch
damage. Oil leaks from the engine rear main bearing seal
or from the transmission front bearing retainer seal can
reach the clutch disc. If the disc gets contaminated with
oil, it grabs or chatters when engaged. If enough oil gets on
the disc, it slips at all times and the disc surfaces soon wear
out from the resulting friction. If the disc becomes com-
pletely saturated with oil, the surface does not wear out,
but the disc itself becomes useless.
Finally, many clutch problems are due to lack of
maintenance or careless service. If the clutch linkage is
not adjusted and lubricated on schedule, or if the
throwout bearing or clutch hub splines are not properly
greased during installation, the moving parts may hang
up or operate slowly. The clutch is subjected to undesir-
able slippage, shortening its life. Slippage and other
problems exhibited in clutch operation are presented in
detail in the upcoming paragraphs. Figure 7-2 summa-
rizes some common conditions and their causes and
corrections.
Clutch Drag
If the clutch cannot be disengaged or it fails to
release, you cannot shift gears. In this situation, when you
stop the vehicle in gear (clutch pedal depressed), the
engine stalls. This condition is known as clutch drag.
Clutch drag varies in degree. Slight drag when the
clutch pedal is fully depressed may tend to make the car
creep when in gear or cause gear clash when the gears are
first engaged. The two most common causes of slight drag
are improper linkage adjustment and lack of lubrication at
the moving parts of the linkage.
In some cases, the car creeps during the clutch
spindown, wherein the disc continues to spin for several
seconds after being disengaged. To determine if this is
causing the creeping and not clutch drag, a simple test can
be performed (if the transmission is not fully synchro-
nized). Depress the clutch pedal, shift into Neutral, and
wait about 30 seconds. Then, shift into an unsynchronized
gear, usually reverse. If the gear engages smoothly, the
creeping is caused by spindown, which is normal. If the
gear clashes, the creeping is caused by clutch drag.
(Consult Chapter 8 for an explanation on synchronizers.)
Clutch drag can be caused by a clutch linkage that is
loose, disconnected, or inoperable. The clutch fork inside
the clutch housing may be disconnected from the
throwout bearing. A hydraulic linkage may be low on
fluid—the reservoir may be empty, or the cylinders or lines
may be leaking. There might be air in the system. A discon-
nected linkage or clutch fork or a dry hydraulic system is
characterized by a pedal that requires little, if any, effort to
depress. A spongy pedal is the result of air in a hydraulic
linkage.
Another possible cause of clutch drag is misalignment
of the transmission or clutch housing. This can happen as
a result of loose bolts or as a result of debris between the
mounting faces. Misalignment can cause the linkage or
internal clutch parts to stick temporarily. Pedal effort will
be normal or higher than normal.
Clutch drag can also be caused by a worn or frozen
pilot bearing, a sticking or warped clutch disc, or a warped
pressure plate or flywheel. A worn disc may become so
overheated, it welds itself to the pressure plate. When
these defects occur, the clutch linkage is working properly
but the engine and transmission remain mechanically
connected.
One of the most common causes of a dragging clutch
is too much pedal free travel. With excessive free travel,
the pressure plate may back off somewhat, but it will still
retain contact with the disc when the pedal is pushed to
the floor. Always check the clutch linkage adjustment
when indications point to a dragging clutch.
Clutch Slippage
Clutch slippage is a condition wherein the full power
of the engine does not reach the transmission. The engine
Chapter 7 Clutch Problems, Troubleshooting, and Service 127