GMC 1989 Light Duty Truck Repair Manual page 219

12-INCH RING GEAR (ROCKWELL)
S U B J E C T
D escription............................................................................................................................................................................... 4B 6- 1
Disassembly of the Rear A xle............................................................................................................................................. 4B 6- 1
C le a n in g .................................................................................................................................................................................... 4B 6- 5
Inspection..................................................................................................................................................................................4B 6- 5
Assembly of the Rear A x le ..................................................................................................................................................4B 6- 6
S p e c ific a tio n s ............................................................................................................................................................................. 4B 6-10
Special T o o ls ............................................................................................................................................................................... 4B6-11
DESCRIPTION
The Rockwell 12-inch ring gear rear axle uses a
conventional ring and pinion gear set to transm it the
driving force of the engine to the rear wheels, this gear set
transfers this driving force at a 90 degree angle from the
propeller shaft to the drive shafts.
This axle is full-floating. The axle shaft is supported at
the wheel ends by the wheel hubs. The rear axle shaft is
held into the rear axle by an axle cap bolted to the hub.
The splined end of the sh aft is supported by the
differential.
This axle uses a differential carrier, separate from the
axle housing. This differential carrier holds the entire
drive gear set, the differential bearings and adjusting
nuts, and the differential bearing caps. The pinion cage is
bolted to the differential cage.
The pinion gear is supported in a pinion cage by three
bearings: a pinion front bearing, a pinion inner bearing,
and a pinion rear or pilot bearing. The pinion cage is
separate from the axle housing. Selective shims are used
between the pinion cage and the axle housing to set the
pinion depth.
The ring gear is bolted onto the differential case with
right-hand thread bolts.
The differential case is supported in the case by two
tapered roller bearings. The differential and ring gear are
located in re latio n ship to the pinion by using two
differential bearing adjusting nuts. These allow the
differential to be moved from side to side by adjusting the
nuts in or out. The differential side bearing preload is
a ccom plishe d by tig h te n in g the d iffe re n tia l bearing
adjusting nuts after the ring gear backlash has been set.
Two bearing caps are used to hold the differential into the
differential carrier as well as to supply half of the threads
for the bearing adjusting nuts.
12-INCH RING GEAR (ROCKWELL) 4 B 6 -1
SECTION 4B6
CONTENTS
The differential is used to allow the wheels to turn at
different rates of speed while the rear axle continues to
transmit the driving force. This prevents tire scuffing when
going around corners and prevents premature wear on
internal axle parts.
The rear axle is sealed with a pinion seal, a gasket at
each axle shaft end, and by a gasket between the rear
axle housing and the differential carrier.
The Rockwell axle is identified by the model number on
the carrier. This axle has a separate carrier, an overhung
pinion, and incorporates disk brakes.
DISASSEMBLY OF THE
Rem ove or D isconnect (Figures 1 and 2)
Tools Required:
• Drain the axle lubricant from the housing.
1. Axle shafts. Refer to the proper service manual.
2. Carrier to housing bolts (47) and washers (45).
• Loosen but do not remove the two upper bolts
3. Carrier (46) from the axle housing.
• Using a roller jack, support the carrier, and
• Use a rawhide hammer to break the carrier
• Remove the two upper bolts (47).
• Place the carrier in a suitable holding fixture (figure
3).
REAR AXLE
J 22912 Split Type Puller Plate
J 7804-01 Pinion Flange Puller
J 22912 Rear Pinion Bearing Remover
J 3453 Pinion Flange Holding Bar
to keep the carrier from falling.
remove it from the axle housing.
loose from the housing.
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P A G E