GMC 1989 Light Duty Truck, Repair Manual, Page: 145 / 998

7’ fe AND 7
5
/s-INCH RING GEAR AXLES 4B1-9
8
.
Preload should be at or below 2.7 to 3.6 N m
(24 to 32 in. lbs.) on new bearings, or 1.0 to 1.4
N m (8 to 12 in. lbs.) for used bearings.
• If the preload torque is below the preloads
given above, continue torquing the nut in small
increm ents. C heck the preload after each
tightening. Each tig hte nin g increases the
bearing preload by several pounds. If the
bearing preload is exceeded, the pinion will
have to be removed, and a new collapsable
spacer installed.
• Once a preload of 2.7 to 3.6 N m (24 to 32 in.
lbs.) has been obtained, rotate the pinion
several times to assure that the bearings have
seated. Recheck the preload, and adjust if
necessary.
Differential case. Refer to “ Backlash Adjustm ent” in
this section.
BACKLASH ADJUSTMENT
1. Install the differential case, bearing cups, spacers,
and shims as determined from the “ Side Bearing
Preload Adjustm ent” earlier in this section.
Rotate the case several tim es to seat the bearings.
Install a dial indicator to the case using a magnetic
base.
Place the indicator stem at the heel end of a tooth
(figure 16).
• Set the dial indicator so that the stem is in line
with the gear rotation and perpendicular to the
tooth angle.
Install the differential bearing caps (31) and bolts
(32).
2
.
3.
4.
5.
T ighten
• The bolts to 75 N m (55 ft. lbs.).
6 . Check and record the backlash at three or four
points around the ring gear.
• The pinion must be held stationary when
checking backlash.
• The backlash should be the same at each
p oint w ithin 0.05 mm (0.002-inch). If the
b a c k la s h v a rie s m o re th a n 0.05 mm
(
0
.
002
-inch), check for burrs, a distorted case
flange, or uneven bolting conditions.
7. Backlash at the m inim um lash point measured
should be between 0.13 and 0.23 mm (0.005 and
0.009-inch) for all new gear sets.
Figure 17— Installing the Differential Bearing
Preload Shim
8 . If the backlash is not within specifications, move the
ring gear in or out from the pinion by increasing the
th ic k n e s s of one s h im , and d e c re a s in g th e
thickness of the other shim by the same amount.
This will maintain the correct rear axle side bearing
preload.
• Moving 0.05 mm (0.002-inch) worth of shim
from one side of the differential to the other
will change the backlash adjustment by 0.03
mm ( 0 . 001 -inch).
9. When the backlash is correctly adjusted, remove the
bearing caps and the shim packs.
10. Select a shim 0.10 mm (0.004-inch) thicker than the
one removed from the left side. Insert this shim
between the spacer and the left bearing race (figure
17).
11. Install the left bearing cap and bolts.
• Do not tighten.
12. Select a shim 0.10 mm (0.004-inch) thicker than the
one removed from the right side. Insert the shim
between the spacer and the right bearing race, and
drive the shim into place (figure 17).
13. Install the right side bearing cap, and bolts.
T ighten
• All bearing cap bolts to 75 N m (55 ft. lbs.).
14. Recheck the backlash and correct as necessary.
FINAL ASSEMBLY
Install or C onnect
1. Drive axles. Refer to the proper service manual.
2. A new cover gasket and the cover (34).
+4-
Tig h ten
• The cover bolts (35) to 27 N m (20 ft. lbs.).
3. Axle housing to the vehicle. Refer to the proper
service manual.
4. Lubricant to the rear axle.