Chevrolet Chevelle 1977 Repair Manual page 146

4B-74
CASE HALF-L.H
SHIM
or greater, the differential will not lock as the added
traction is not necessary.
Service Test Procedure
1. Place the Truck on a frame-contact hoist, allowing
free rotation of the rear wheels.
2. Raise hoist until wheels clear floor. Holding one wheel
stationary, slowly rotate other wheel approximately 1/2
revolution per second, in both the forward and reverse
directions. Wheel should rotate freely. If both wheels attem pt
to turn together, the differential is locking and is defective.
NOTE:
Rapid wheel rotation will cause a properly
operating differential to lock and both wheels will rotate
in the same direction.
3. Raise hoist to maximum height with one person in
vehicle.
4. Start engine making sure that carburetor is set to
provide a low idle speed of 600-800 rpm.
5. Place transmission in drive range and apply brakes.
W ith m anual transmission,
transmission in first gear.
6. Lock one rear wheel by pulling one parking brake
cable from under the vehicle.
7. W ith engine at low idle, slowly release brakes. With
manual transmission, slowly engage clutch.
8. Locked rear wheel will remain stationary and free
wheel will begin turning. It is im portant that brakes or clutch
be released slowly enough to start the free wheel turning and
OVERHAUL MANUAL
GUIDE CLIP (6)
SIDE GEAR
EARED DISC (3)
SPLINED DISC (2)
LATCHING BRK'T ASS'Y
Fig. 4 B - 2 H -3 /4 Ton U n it
depress clutch and place
GUIDE CLIP (6)
DISC PACK S/A
CASE HALF-R.H
GOVERNOR ASS'Y
allow the free wheel to gradually increase in speed. As speed
of the free wheel is increased, the differential will lock causing
the rotating wheel to stop or both wheels to turn at the same
speed. The engine may stall if equipped with a manual
transmission. It may be necessary to accelerate engine until
approximately 10 m ph is indicated on vehicle speedometer
to cause differential lock. If indicated speed can be increased
beyond 20 m ph without causing differential lock, the unit is
not functioning properly.
NOTE:
Rapid release of brakes or clutch, or rapid
acceleration of engine will invalidate test.
9. Lock opposite rear wheel and repeat procedure. The
following chart provides guidelines for diagnosis and repair
of differential complaints.
OVERHAUL PROCEDURES 8 -7 /8 RING GEAR
AXLE 1 /2 TON TRUCKS
CAUTION: Due to critical internal clearance
dimensions, differential side gears and case cannot
be serviced separately. I f any side gear or case
damage is found, the entire differential must be
replaced.
Internal clearances are such that shims,
reaction block, and thrust rings should not be
replaced unnecessarily even
indications are present. I f shims, reaction block, or
thrust ring must be replaced due to damage, correct
measurement and replacement procedures must be
SCREW (3)
SHIM
THRUST WASHER (3)
PINION GEAR (3)
PINION YOKE
THRUST BLOCK (2)
i f slight wear