Clutch
Symptoms and Their Causes
(it’s Not Really Rocket Science!)
Here
is a quick explanation of likely causes for
various clutch problems. Where possible, I
mention them in order of their likelihood.
In all cases, I am assuming the clutch in
the vehicle is the right one, it is correctly
installed, and there has been no tampering
to deliberately cause a problem. I am addressing
only normal use situations.
Slippage:
The
classic clutch symptom is slippage. Engine
revolutions are not fully transferred to the
transmission. Power is not fully transmitted
to the drive wheels. The engine seems to race
but the vehicle does not keep up! Slippage
is most often caused by a worn clutch disc.
Or, the clutch pressure plate may be weakened
by heat, age, or abuse. In either case, it
means the vehicle needs a new clutch. Replacing
just one clutch part is not good practice.
Automotive repair professionals will not attempt
such partial repairs. Worn or damaged clutches
must be replaced.
Less
common causes of slippage include: massive
amounts of oil on the clutch (usually causes
chatter, not slippage, see below), a broken
disc or pressure plate, a release cable binding,
or transmission damage. Obviously, an oil-soaked
or broken clutch requires replacement. But,
even when the problem is external, replacing
a slipping clutch may be warranted. Slippage
causes almost instant damage to the clutch.
Heat produced by the slippage quickly damages
friction material, contact surfaces, and springs.
Clutch
Release Problems:
Clutch
release problems are common. Even though the
clutch pedal is depressed, you have trouble
shifting. In some cases it is impossible to
get the transmission into gear. Sometimes
there is an accompanying sound of grinding
gears! When these symptoms occur, they are
most often the result of the clutch not fully
disengaging. The transmission input shaft
is not allowed to come to a stop. Engine revolutions
are still being transmitted to the transmission.
Sources for this problem vary according to
the type of clutch mechanism your vehicle
has.
Mechanical
Linkage:
Worn
pivot points, broken or bent push rod, worn
or broken cross-shaft, bent pedal bracket,
or cracked firewall can each cause this problem.
Usually, several parts are contributing to
the problem. This type of mechanism tends
to wear and fail with age and continued use.
Cable
Operated Clutch:
Stretched,
frayed or binding cable, broken or bent pedal
bracket, or cracked firewall can be the cause.
Problems with a cable mechanism will often
herald internal clutch problems as well. When
something happens inside the clutch that requires
extra force to be exerted on the clutch pedal,
things break! Cables can also wear simply
from age and use.
Hydraulically
Operated Clutch:
Clutch
master cylinder leaking or bypassing pressure,
slave cylinder leaking, clutch flex hose leaking,
pedal bushings worn or missing, or a cracked
firewall can reduce the system’s ability
to disengage the clutch. Rule of thumb: If
the clutch master cylinder is bad, replace
both master and slave cylinders as a pair.
This will save you future heartache.
Internal
clutch Release Problems:
Not
all release problems are caused by the release
mechanism. Things can go wrong inside the
clutch as well. A loose damper spring in the
clutch disc, bent disc, frozen pilot bearing,
collapsed release bearing, or metal shrapnel
from a broken cover can cause the clutch to
bind and not fully release when the pedal
is depressed. The release fork might bend.
The pivot ball can wear or break. There are
many reasons for a clutch to hang up.
Clutch
Chatter:
Clutch
chatter, a vibration and/or noise when engaging
the clutch, is likely to be caused by an internal
clutch problem. A warped disc, hotspots on
the flywheel or pressure plate surfaces, worn
or dry input shaft splines, or worn release
bearing.
|
