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CLUTCH
7C-1
SECTION 7C
CLUTCH
CONTENTS OF THIS SECTION
General Description
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7C-1
Diagnosis
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7C-3
Maintenance and Adjustments
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7C-3
On-Car-Service
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7C-6
Clutch Pedal Replacement
...............................
7C-6
Clutch Cross Shaft Replacement
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7C-6
GENERAL DESCRIPTION
The principal parts of a clutch are: the driving members,
attached to the engine and turning with it; the driven
members, attached to the transmission and turning with it;
the operating members which include the spring or springs
and the linkage required to apply and release the pressure
which holds the driving and driven members in contact with
each other. Figure 7C-1 shows a clutch cutaway so that
operating members can be seen.
DRIVING MEMBERS
The driving members of a clutch usually consist of two
nodular iron plates or flat surfaces machined and ground to
a smooth finish. Nodular iron is desirable because it contains
enough graphite to provide some lubrication when the driving
member is slipping during engagement. One of these surfaces
is usually the rear face of the engine flywheel, and the other
is a comparatively heavy flat ring with one side machined and
surface. This part is known as the pressure plate. It is fitted
into a steel cover, which also contains some of the operating
members, and is bolted to the flywheel.
DRIVEN MEMBERS
The driven member is a disc with a splined hub which
is free to slide lengthwise along the splines of the clutch shaft,
but which drives the shaft through these same splines.
Grooves on both sides of the clutch driven plate lining
prevent sticking of the plate to the flywheel and pressure plate
due to vacuum between the members on disengaging. The
clutch driven plate is usually made of spring steel in the shape
of a single flat disc consisting of a number of flat segments.
Suitable frictional facings are attached to each side of the
plate by means of brass rivents. These facings must be heat
resistant since friction produces heat. The most commonly
used facings are made of cotton and asbestos fibers woven or
molded together and impregnated with resins or similar
binding agents. Very often, copper wires are woven or pressed
into material to give it additional strength.
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Clutch Cable Replacement
,
7C-6
Unit Repair
...........................................................
7C-8
Clutch Assembly Replacement
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7C-8
Pilot Bearing Replacement
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7C-1
1
Special Tools
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7C-1 1
In order to make clutch engagement as smooth as
possible and eliminate chatter, the steel segments attached to
the splined hub are slightly waved, which also causes the
facings to make gradual contact as the waved springs flatten
out.
The driven member of the clutch (Fig. 7C-2) is usually
provided with a flexible center to absorb the torsional
vibration of the crankshaft which would be transmitted to the
power train unless it were eliminated. The flexible center
usually takes the form of steel compression springs placed
between the hub and the steel plate. The springs permit the
disc to rotate slightly with relation to its hub until, under
extreme conditions, the springs are fully compress and
relative motion stops. Then the disc can rotate slightly
backward as the springs decompress. This Slight backward
and forward rotation permitted by the springs allows the
clutch shaft to rotate at a more uniform rate than the
crankshaft, thereby eliminating some of the torsional
vibration from the crankshaft and preventing the vibration
from being carried back through the transmission.
OPERATING MEMBERS
The driving and driven members are held in contact by
spring pressure. This pressure is exerted by a one-piece
conical or diaphragm spring (Fig. 7C-3). The throwout
bearing moves forward against the spring fingers forcing the
diaphragm spring to pivot around the inner pivot ring,
dishing the fingers toward the flywheel. The outer
circumference of the spring now lifts the pressure plate away
from the driven disc, through a series of retracting springs
placed around the outer circumference of the pressure plate.
NOTE: Two variations of the diaphragm spring design
are the flat finger type and the bent finger type. The
integral release fingers in the bent finger design are bent
back to gain a centrifugal boost to aid quick re-
engagement at high engine speeds. This design is used
primarily with high performance V8 engines and
passenger car heavy duty clutch assemblies.
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