•
A warped or damaged pressure plate
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Improper adjustment of the pressure plate release lever (Some pressure plates
require this adjustment before the part is installed.)
To correct clutch dragging, adjust the free travel. Make this adjustment according to the
manufacturer's specifications. If the problem is not corrected with this adjustment, you
may need to remove the clutch for repairs or replacement.
1.1.2 lipping
Because of heat generation, slipping of the clutch (while it is engaged) can severely
damage the clutch disc facings. The contact surfaces on the pressure plate and the
flywheel may also be damaged. If a clutch is allowed to continue to slip, complete clutch
failure may result. Clutch slipping is most obvious when you are just starting out from a
dead stop or upon sudden acceleration in a low gear. Slipping will be very noticeable in
a vehicle with a heavy load.
Causes of clutch slippage include incorrect clutch pedal free travel, binding in the clutch
linkage, and "riding the clutch." If the free travel is insufficient, there is a tendency for the
release bearing to contact the release levers, even though the operator's foot is off the
clutch pedal. As a result, the clutch disc may not be clamped tightly between the
flywheel and the pressure plate. Readjustment of the pedal free travel will solve this
problem. If you do not adjust the free travel at once, the release bearing, as well as the
clutch disc, will wear rapidly.
If a binding condition exists in the clutch linkage, the pedal will be reluctant to return
when it is released. So again, you may encounter clutch slippage. To solve this
problem, "free up" the linkage that is binding by simply lubricating or aligning the clutch
linkage. If this fails to correct the problem, you may have to remove the clutch for further
inspection and repair.
"Riding the clutch" is an operator problem whereby the operator steadily drives with a
foot on the clutch pedal. As a result, the pedal may be partially depressed and cause
clutch slippage. If this form of operator abuse is suspected, contact the transportation
supervisor. The problem should be corrected through proper operator training.
1.1.3 1.1.3 Grabbing
Occasionally, you may encounter a clutch that grabs or chatters, no matter how evenly
or gradually you try to engage it. If the linkage operates satisfactorily and the engine
and clutch mountings are not loose, you may have to remove the clutch assembly from
the vehicle to cure the trouble. The probable causes are loose, glazed, oily, or greasy
disc facings; binding of the disc on the clutch shaft; broken or otherwise defective
pressure plate springs; or a broken or otherwise defective pressure plate
.
A careful inspection of all clutch parts should reveal any defective items. In any case,
replace any damaged parts and rebuild the clutch as specified by the manufacturer. In
most cases, it is best that you install the clutch as a unit, which includes replacing the
clutch disc, pressure plate, release bearing, and pilot bearing, and resurfacing the
flywheel. Replacing the complete assembly prevents the need for rework.
1.1.4 Noises
A noisy clutch may be caused by a number of conditions. Most of these conditions can
be corrected only after you have removed the assembly from the vehicle. Start your
inspection by noting whether or not the noise occurs when the clutch is engaged or
NAVEDTRA 14050A
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