SECTION-6R

CLUTCH

INDEX
Page Page
General Description 6R-1 Pilot Bearing Replace 6R-5
Maintenance and Adjustments 6R-2 Assembly 6R-6
Inspection 6R-2 Installation 6R-8
Adjustments 6R-3 Clutch Pedal 6R-8
Service Operations 6R-4 Clutch Cross Shaft 6R-8
Clutch Assembly 6R-4 Remove 6R-8
Removal 6R-4 Repair 6R-8
Disassembly 6R-4 Installation 6R-8
Cleaning and Inspection 6R-5 Diagnosis Chart 6R-9

GENERAL DESCRIPTION
The clutch used with Synchromesh transmission move away from center of the assembly as speed is in
equipment from 1955 to 1962 is a single plate dry disc creased and act as wedges between pressure plate and
type. In 1956 a semi-centrifugal feature was added and cover thereby increasing pressure plate force against
carried over to the present date. As more powerful driven disc.
power plants were developed, torque capacity of Individual adjustment is provided for locating each
clutches were increased accordingly. This is done by lever in manufacturing assembly, but the adjusting nut
increasing the spring force in the clutch. is staked in place and should not be disturbed unless
The centrifugal assist is accomplished by use of the clutch is disassembled for replacement of parts.
rollers between pressure plate and cover. The roller The clutch is operated by conventional linkage figs.
is not attached to either the pressure plate or cover 1 and 2 assisted by an over-center spring. The linkage
but is guided by a channel on the pressure plate and consists of a pendant type pedal, pedal push rod, cross
retained in the channel by position of the cover when shaft, clutch fork push rod, clutch fork, fork anti
assembled to pressure plate. The rollers are free to rattle spring and over-center assist spring.
The over-center assist spring is located at the pedal
side of the clutch cross shaft figs. 1 and 2. In 1958
the spring attachment at the cross shaft was revised to

Hg. 1 -Clutch LInkage 55-57 Fig. 2-Clutch Linkage 58-62

CLUTCH 6R-2

provide for variable tension adjustment of the over- gines in 1962. The first clutch used with hydraulic
center spring fig. 2. lifter engines has a pressure plate of gray cast iron
In 1959 a dual position pedal bracket was introduced and uses stronger springs. The second clutch heavy-
fig. 5 which made a fast release possible by reposi duty-used with mechanical lifter engines has a pres
tioning the bracket on the pedal and thus changing the sure plate cast of extremely high tensile strength pear
length of effective lever arm that attaches to the push litic malleable iron. It is identified by a groove 1/8" x
rod. %" cast in each drive lug insert, fig. 3.
Two new clutch assemblies both with a much The two clutches look alike, but the first must not
higher pressure plate load are used to provide ade be installed on a mechanical lifter engine while the
quate torque capacity for the new 327 cubic inch en- second can be used interchangeably.

Fig. 3-Clutch Assembly Cross-Section

1. Release Lever 4. Cover 7. Driven Plate 10. Throwout Bearing
2. Eyebolt 5. Adjusting Nut 8. Pressure Plate 11. Flywheel
3. Strut 6. Coil Spring 9. Anti.rattle Spring

MAINTENANCE AND ADJUSTMENTS

LINKAGE INSPECTION travel decreases with wear, as much as 3/4" to
1" is allowed on a new vehicle or at time of
There are several things which affect good clutch readjustment, however, the efficiency is not
operation. Therefore, before performing any major impaired until the free travel is zero or less.
clutch operations, it is necessary to make preliminary Clutch should not be operated at zero lash for
inspections to determine whether the trouble is actual any length of time as it will soon wear to less
ly in the clutch. than zero and slip, causing overheating and
permanent damage.
1. Check linkage to be sure the clutch fully releases
as follows: b. With engine running at idle speed, hold the
clutch approximately 1/2" from the floor mat
a. Check free travel of pedal, that is, pedal move and move shift lever between neutral and re
ment from its return bumper stop to a position verse several times. If shift is not smooth
that causes the release bearing on inside end especially into reverse on 4-speed, the clutch
of fork to begin to apply pressure to the clutch is not fully releasing and clutch free pedal
release levers lifting the pressure plate, is travel or clutch total travel adjustment is neces
necessary to ascertain that the clutch is work sary. If clutch releases ok and linkage operation
ing at its maximum efficiency. Since this free is smooth, omit the following steps.
 CLUTCH 6R-3

2. If clutch pedal release check is not satisfactory

and free pedal travel is ok, check "Clutch Pedal c. Check free pedal travel at pedal.
Total Travel" as outlined in this section. 2. On 1958 through 1962 Corvettes fig. 5.
3. Check clutch pedal bushings for sticking or exces
sive wear and clutch lever and shaft assy. for
lubrication at ball studs.
4. Loose or damaged engine mounts may allow the
engine to shift and cause a bind on the clutch
linkage at the cross shaft.
5. Check for bent, cracked or damaged outboard
cross shaft bracket.
6. Check for proper over-center spring adjustment.
Disconnect fork push rod and adjust arm on
clutch cross-shaft assy. so that load required to
push pedal away from bumper is 6-9 lb.

CLUTCH PEDAL FREE TRAVEL ADJUSTMENT Fig. 5-Free Pedal Adjustment 58-62
This adjustment sets the amount of pedal travel
from the return bumper position to point of release a. Disconnect lower push rod swivel from cross
bearing contact with clutch release levers in the clutch shaft lever.
assembly. This travel, when resetting, should be as b. Hold push rod in direction of clutch release so
close to 1" as possible for maximum wear allowance. that throwout bearing is against clutch release
Do not confuse lash feel and over-center feel. The fingers, then adjust swivel to freely enter hole
over-center assist spring opposes the initial approxi in cross shaft lever. This removes all pedal lash.
mately ½" pedal movement, but the pedal can be
depressed over this part by hand and then a very c. Shorten the push rod to get proper lash by
noticeable increase in pressure is felt when throwout turning swivel 2 turns onto the rod, then con
bearing contacts throwout fingers. nect swivel to cross shaft lever.
If necessary, adjust as follows: d. Check free pedal travel at pedal.
1. On 1955, 1956 and 1957 Corvettes fig. 4.
a. Loosen jam nut 1, then turn adjusting nut CLUTCH PEDAL TOTAL TRAVEL ADJUSTMENT
2 until all lash is removed at clutch fork. Clutch pedal total travel is the chord of the arc
b. Shorten the rod two turns of the adjusting nut traveled by the pedal pad from its bumper stop posi
and tighten jam nut 1. tion to its floor stop position during clutch release as
shown in Figure 6. This dimension should be approxi
mately 6/2 inches 4½ on fast release position-late
model vehicles measured as follows:
1. With pedal held against floor stop, measure dis
tance "A" fig. 6.
NOTE: Distance "A" may be as little as 1/e ".

2. Release pedal to its bumper stop and measure dis

tance "B" fig. 6.
3. Subtract distance "A" from distance "B" and the
result is pedal travel.
4. To increase travel trim rubber bumper as neces
sary-to decrease adjust free pedal travel as
necessary.

PEDAL REPOSITIONING ADJUSTMENT

Normal setting of, the clutch pedal linkage results in
a total pedal travel of approximately 6½". A second
Fig. 4-Free Pedal Adjustment 55-57 setting available since 1959 is provided in the link-
CLUTCH 6R-4

3. Loosen push rod bracket to pedal lower attaching

bolt in slotted hole "B", Figure 7.
4. Remove the upper bolt from hole "C", and rotate
the bracket until hole "A" is aligned with upper
hole in pedal arm, then install bolt, lockwasher
and nut.
5. Tighten both upper and lower bolts.
/

6. Install clutch pedal push rod so the bend as

shown in Figure 7 is in opposite direction from
its previous installed position.
7. Remove block from cross shaft lever and check
for free pedal play, proper clutch release, and new
total pedal travel distance if necessary.
8. Readjust lash to ½ to ¾" for low pedal position.

Fig. 6-Pedal Total Travel Adjustment

age to reduce the pedal travel to approximately 4½",

which provides the precision feel of the fast release
and permits more rapid gear shifting. The adjustment
is accomplished by relocating the pedal push rod pin
bracket as follows:
1. Wedge a block between the cross shaft upper
lever and the toe pan to hold the pedal just off
bumper stop.
2. Disconnect clutch pedal push rod at both ends. Fig. 7-Pedal Repositioning Adjustment

MAJOR SERVICE OPERATIONS

CLUTCH ASSEMBLY NOTE: It is advantageous to place nuts or
metal spacers between the 3 clutch levers and
Removal from Vehicle the cover to hold the levers down during
1. Remove transmission as outlined in transmission removal.
section. 6. Support clutch disc and pressure plate assembly
with one hand and remove Tool J-5824, then lower
2. Remove flywheel underpan. clutch assembly from vehicle.
3. Remove throwout bearing from clutch fork.
Disassembly
4. Install Tool J-5824 to support the clutch assembly
during removal. 1. Place the cover assembly on the bed of an arbor
or drill press with a block under the pressure plate
NOTE: Look for "X" mark on flywheel and on so arranged that the cover is left free to move
clutch cover. If "X" mark is not evident, prjck down.
punch marks on flywheel and clutch cover for
indexing purposes during installation. 2. Place a block or bar across the top of the cover
and compress the cover with the spindle. Hold
5. Loosen the clutch-to-flywheel attaching bolts even compressed while the adjusting nuts are removed
ly 1 turn at a time until spring pressure is re as shown in Figure 8, then slowly release pres
leased, then remove the bolts. sure to prevent springs flying out.
 CLUTCH 6R-5

Fig. 8-Compressing Clutch

Fig. 11-Removing Levers Step 2

1. Release Lever 2. Eyebolt 3. Strut

NOTE: It is important to replace all parts which

show wear.

Inspection and Repair

1. Wash all parts, except driven disk and throwout
bearing, in cleaning solvent.
Fig. 9-Dismantling Clutch NOTE: The throwout bearing is permanently
packed with lubricant and should not be
3. Lift off cover and all parts will be available for soaked in cleaning solvent as this may dissolve
inspection. Note carefully the location of all parts the lubricant.
including arrangement of the springs. 2. Inspect pressure plate and flywheel for scores on
4. To remove levers grasp lever and eyebolt be the contact surfaces. Use a straight-edge and check
tween thumb and fingers as shown in Figure 10, for flatness of contact surfaces.
so that inner end of lever and upper end of eye- 3. Check drive Jugs for looseness at the clutch cover
bolt are close together, keeping eyebolt pin seated and evidence of looseness at pressure plate bolt
in its socket in lever. holes.
4. Check throwout bearing for roughness and free
fit on the sleeve of the transmission clutch gear
bearing retainer.
5. Inspect clutch disc for worn, loose or oil soaked
facings, broken springs, loose rivets or riding.
6. Examine splines in hub and make sure they slide
freely on splines of transmission clutch shaft. If
splines are worn, the clutch disc or clutch gear
should be replaced as necessary.
7. Inspect clutch fork ball socket and fingers for
wear and ball retaining spring for damage.
8. Inspect ball stud for wear.
Fig. 10-Removing Levers Step 1
Pilot Bearing
1. Release Lever 2. Eyebolt 3. Strut
The clutch pilot bearing is an oil impregnated type
5. Lift strut over ridge on end of lever, fig. 11. bearing pressed into the crankshaft. This bearing re
quires attention only when the clutch is removed
6. Lift lever and eyebolt off pressure plate. from the vehicle, at which time it should be cleaned
CLUTCH 6R-6

lOcJ

Fig. 12-Coil Spring Clutch-Exploded

1. Pressure Plate 3. Eyebolt 5. Release Lever 7. Adjusting Nut 9. Anti-Rattle Spring

2. Coil Spring 4. Pin 6. Strut 8. Cover 10. Centrifugal Roller

and inspected for excessive wear or damage and should placing this bearing, use Tool J-1522. Place bearing on
be replaced if necessary. To remove, install Tool J-1448 pilot of tool with radius in bore of bearing next to
and remove bearing from crankshaft fig. 13. In re shoulder on tool and drive into crankshaft.

Assembly
1. Lay the pressure plate on the block in the press
and coat the lugs with a thin film of approved
lubricant such as lubriplate as shown in Figure

Fig. 13-Clutch Pilot Bearing Removal Fig. 14-Greasing Drive Lug

 CLUTCH 6R-7

14. Also, apply a light film of high melting point 7. Assemble anti-rattle springs in cover as shown in
graphite grease in the eyebolt holes in the pres Figure 16. The spring to the left is in operating
sure plate. position.

2. Assemble lever, eyebolt and pin, holding eyebolt 8. Install centrifugal rollers in proper seats, as shown
and lever as close together as possible and with in Figure 17.
the other hand grasp strut as shown in Figure 15.

Fig. 15-Installing Levers

3. Insert strut in the slots in the pressure plate lug,

drop slightly and tilt the lower edge until it
touches vertical milled surface of lug.
4. Insert lower end of eyebolt in hole in pressure
plate. The short end of the lever will then be un
der the hook of the pressure plate and near the
strut fig. 11. Fig. 17-Installing Rollers

5. Slide the strut upward in the slots of the lug, lift

ing it over the ridge on the short end of the lever 9. Lower the cover on top of the assembled parts,
and drop it into the groove in the lever fig. 10. fig. 18 being sure that the anti-rattle springs
are in correct position and also that the punch
6. Assemble the pressure springs, on the small bosses marks made before dismantling are matched to
of the pressure plate in accordance with the order insure retaining the original balance.
of removal.
10. Place a bar across the cover, as shown in Figure
8 and slowly compress, guiding the holes in the
cover over the pressure plate Jugs and all springs
into their spring seats in the cover.
11. Assemble adjusting nuts on the eyebolts and
screw them down until their tops are flush with
the tops of the eyebolts. Slowly release pressure
of spindle and remove cover assembly from press.

Adjusting Levers
While no wear adjustment is needed because of the
coil spring design, it is imperative that the clutch re
lease levers are each set to exactly the same height at
the time of manufacture or rebuild to insure uniform
clutch application. To obtain exactly the same adjust
ment at each release lever, use gauge plate J-1048 and
release lever height gauge J-6456 as follows:

NOTE: To adlust levers it is necessary to use

Tool J-O48 on the flywheel in the car or on
Fig. 16-Installing Anti-Rattle Spring a spare flywheel at the bench.
 ________

CLUTCH 6R-8

Fig. 18-Assembling Cover to Pressure Plate

1. Place gauge plate on the flywheel in the position

normally occupied by the driven plate as shown
in Figure 19.

Fig. 20-Depressing Lever

C
Fig. 19-Gauge Plate Position
J.6456
ADJUSTING
J 6456
2. Bolt cover on flywheel with the gauge plate cen
tered and with the three flat machined lands
placed directly under the levers.
3. Depress each lever several times with a hammer
handle as shown in Figure 20 to settle all of the
parts into working position.
4. Make a sheet metal lever height gauge like that
shown in Figure 21 or use Tool J-6456. The step
or notch, should be 1/8", by approximately /16"
Fig. 21-Setting Lever with Height Gauge
long.
5. Lay the height gauge across the hub of the gauge 6. Stake the nuts with a dull punch as shown in
plate and the bearing surface of one lever and Figure 22 driving metal from the nut into the
turn the adjusting nut until the lever is flush with grooves in the eyebolt to provide a secure lock.
the height gauge. Then adjust the other levers in
the same manner. 7. Loosen the holding screws a turn or two at a time
 CLUTCH 6R-9

7. Lubricate the recess on the inside of throwout

bearing collar and the throwout fork groove with
a light coat of graphite grease fig. 23.
8. Install throwout bearing to the throwout fork.
9. Install transmission as outlined in transmission
section.
10. Install flywheel underpan.
Fig. 22-Staking Nut
11. Perform linkage adjustment for over-center spring
until the spring pressure is relieved which will adjustment and pedal free play and check clutch
allow clutch and gauge plate to be removed. release position.

Installation to Vehicle CLUTCH PEDAL

1. Hand crank the engine until the "X" mark on Clutch pedal service operations are outlined in the
flywheel is at bottom. Brake Section of this manual. Refer to Clutch and
Brake Pedal Service Operations, Section 5.
2. Position the clutch disc and pressure plate in rela
tive installed position and support them with
alignment Tool J-5824. Clutch Cross Shaft
NOTE: Clutch driven disc is installed with Removal
damper springs and slinger toward pressure 1. Place a blocking device wood or other between
plate. upper cross shaft lever and toe-pan to hold clutch
3. Turn clutch assembly until "X" mark on cover pedal just off bumper stop.
lines up with "X" mark on flywheel, then align 2. Remove clutch pedal push rod bolt at cross shaft
cover bolt holes to nearest flywheel holes. lever and pin at pedal end, then slide push rod up
into passenger compartment enough to clear cross
4. Install bolts in every other hole first and tighten shaft lever,
down evenly and gradually until tight to avoid
possible clutch distortion, then install the remain 3. Raise vehicle on hoist or stand jacks.
ing bolts.
4. Disconnect clutch fork push rod from cross shaft
5. Remove pilot tool. lever.
6. Unhook clutch fork and lubricate ball socket with 5. Hold lower cross shaft lever using a 12" crescent
a high melting point grease such as graphite and wrench or slide a deep socket with 12" extension
reinstall on ball stud. over the lever.
6. Move the lever rearward enough to remove block
COAT THIS GROOVE ing device, then move the lever forward to rotate
cross shaft and release tension on over-center
assist spring, then unhook spring.
7. Remove cross shaft bracket-to-engine bolts and
remove the cross shaft and bracket together.

Repair
1. Inspect cross shaft brackets and ball pivots for
wear, damage or bent conditions. Damage to the
PACK THIS RECESS ball requires replacement of brackets and ball.
2. Inspect cross shaft ends for cracks, wear, or other
damage. Damaged cross shafts should be replaced.
3. Inspect felt spacers at each ball pivot. Replace
torn, worn, or excessively compressed felts.

Installation
1. Install felt spacers over each ball pivot.
Fig. 23-Throwout Bearing Lubrication 2. Install cross shaft over frame bracket ball, install
CLUTCH 6R-1O

engine bracket and ball onto opposite end, then 5. Remove leverage tool and connect clutch fork
slide engine bracket into place on engine and in push rod to lower cross shaft lever.
stall bracket bolts.
6. Connect clutch pedal push rod at both ends, then
3. Rotate cross shaft lower lever forward to install remove blocking device from between toe-pan and
assist spring end plate over its mounting pin on lever.
1955-1957 models hook spring into mounting eye.
7. Adjust over-center spring.
4. Using wrench or socket as before, pull lower lever
rearward far enough to install blocking device be 8. Check free pedal play and clutch release feel and
tween toe-pan and upper cross shaft lever. adjust as needed.

TROUBLES AND REMEDIES

Symptom and Probable Cause Probable Remedy
Fails To Release
a. Improper linkage adjustment a. Adjust linkage
b. Improper pedal travel b. Trim bumper stop
c. Loose linkage c. Replace bushings
d. Faulty pilot bearing d. Replace bearing
e. Faulty driven disc e. Replace disc
f. Fork off ball stud. f. Install properly and lubricate fingers at throwout
bearing
g. Clutch disc hub binding on clutch gear spline g. Repair or replace clutch gear
h. Clutch housing misalignment h. See "Clutch Housing Alignment" Section 6
i. Pressure plate fingers not adjusted evenly-Check i. Remove clutch and adjust lever height to varia
pressure plate lift-.055"-070". tion of less than .007".

Slipping
a. Improper adjustment no lash a. Adjust linkage
b. Oil soaked b. Install new disc and correct oil leak at its source
rear main, transmission, or leakage into hous
ing from other engine gasket areas
c. Worn facing or facing torn from disc c. Replace disc
d. Warped pressure plate or flywheel d. Replace same
e. Weak springs e. Replace assembly springs on pressure plate

Grabbing
a. Oil on facing or burned or glazed facings a. Install new disc
b. Worn splines on clutch gear b. Replace transmission clutch gear
c. Loose engine mountings c. Tighten or replace mountings
d. Warped pressure plate or flywheel d. Replace pressure plate or flywheel

Rattling-Transmission Click
a. Weak retracting springs a. Replace springs
b. Throwout fork loose on ball stud or in bearing b. Check ball stud and retaining spring and replace
groove if necessary
c. Oil in driven plate damper c. Replace driven disc

Throwout Bearing Noise with Clutch Fully Engaged

a. Improper adjustment a. Adjust linkage
b. Throwout bearing binding on transmission b. Clean, relubricate, check for burrs, nicks, etc.
c. Insufficient tension between clutch fork spring c. Replace fork
and ball stud
d. Fork improperly installed d. Install properly
e. Weak linkage return spring e. Replace spring
 CLUTCH 6R-11

Symptom and Probable Cause Probable Remedy

Noisy
a. Worn throwout bearing a. Replace bearing
b. Fork off ball stud Heavy clicking b. Install properly and lubricate fork fingers at
bearing

Pedal Stays on Floor When Disengaged

a. Bind in linkage a. Lubricate and free up linkage
b. Over-center spring adjustment b. Adjust
c. Springs weak in pressure plate c. Replace

High Pedal Effort

a. Bind in linkage a. Lubricate and free up linkage
b. Over-center spring adjustment b. Adjust

SPECIAL TOOLS

fo -Jil
91
1LJ

3 4

Fig. 24-Clutch Special Tools

1. .1-6456 Height Gauge 3. .1-1522 Pilot Bearing Driver 5. .1.1448 Pilot Bearing Puller
2. .1.1048 Gauge Plate 4. .1-5824 Clutch Pilot Tool