GMC 1982 Light Duty Truck, Service Manual

Page: 1217 / 1435

CLUTCH 7C -3
The release bearing is moved by the clutch fork to
contact the release levers and move the pressure plate to the
rear, thus separating the clutch driving members from the
driven member when the clutch pedal is depressed by the
driver.
A re tu rn spring preloads clutch linkage, removing
looseness due to wear, keeping the bearing clear of the
spring fingers.
T he clutch free pedal travel, therefore, will increase
with linkage wear and decrease with driven disc wear. The
F ig. 7 C -3 ~ C lu tc h Disc
free travel felt at the clutchpedal is release bearing lash.
Clutch Spring O p era tio n
In diaphragm spring type clutches, a diaphragm spring
is used instead of coil springs. It is a conical piece of spring
steel punched to give it greater flexibility. The dia phragm is
positioned between the cover and the pressure plate so that
the diaphragm spring is nearly flat when the clutch is in the
engaged position. The action of this type of spring is similar
to that of the bottom of an ordinary oil can. The pressure of
the outer rim of the spring on the pressure plate decreases as
the flat position is passed. The outer rim of the diaphragm is
secured to the pressure plate and is pivoted on rings
approximately 25mm (1 in.) in from the outer edge so th at
the application of the pressure at the inner section will cause
the outer rim to move away from the flywheel and draw the
pressure plate away from the clutch disc, releasing or
disengaging the clutch. W hen the pressure is released from
the inner section, the oil-can action of the diaphragm causes
the inner section to move out, and the movement of the outer
rim forces the pressure plate against the clutch disc, thus
engaging the clutch.
COIL SPRING CLUTCH
The coil spring single plate clutch (Fig. 7C-4) is a dry
disc type and no adjustm ent for wear is provided in the
clutch itself. An individual a d ju stm e n t is provided for
locating each lever in m anufacturing but the adjusting nut is
locked in place and should never be disturbed, unless the
clutch assembly is dismantled for replacement of parts.
W hen the clutch pedal is depressed the release bearing
is moved toward the flywheel and contacts the inner ends of
1. R e le a se L e v e r 7 . D r iv e D is c
2. E y e b o lt
8 . P re s s u re P la te
3 . S t r u t
9 . A n t i - R a t t l e S p r in g
4 . C o v e r
1 0 . C lu t c h R e le a s e B rg .
5.
A d j u s t m e n t N u t
1 1 . F ly w h e e l
6 . C o il S p r in g
102703
FRICTION
RING
HUB
FLANGE
STOP PIN
C U S H IO N SPRINGS
DRIVE
W ASHER
FA C IN G S
T O R S IO N A L
COIL SPRINGS
Fig. 7C-4--Cross-Section View o f Coil Spring Type