Jeep Cherokee (XJ): 186 FBI differential bearing preload and gear backlash

INTRODUCTION

Differential side bearing preload and gear backlash is achieved by selective shims positioned behind the differential side bearing cones. The proper shim thickness can be determined using slip-fit dummy bearings D-348 in place of the differential side bearings and a dial indicator C-3339. Before proceeding with the differential bearing preload and gear backlash measurements, measure the pinion gear depth and prepare the pinion for installation. Establishing proper pinion gear depth is essential to establishing gear backlash and tooth contact patterns. After the overall shim thickness to take up differential side play is measured, the pinion is installed, and the gear backlash shim thickness is measured. The overall shim thickness is the total of the dial indicator reading and the preload specification added together.

The gear backlash measurement determines the thickness of the shim used on the ring gear side of the differential case. Subtract the gear backlash shim thickness from the total overall shim thickness and select that amount for the pinion gear side of the differential (Fig. 94). Differential shim measurements are performed with axle spreader W-129-B removed.

Fig. 94 Axle Adjustment Shim Locations

1 - PINION GEAR DEPTH SHIM/OIL BAFFLE
2 - DIFFERENTIAL BEARING SHIM

SHIM SELECTION

NOTE: It is difficult to salvage the differential side bearings during the removal procedure. Install replacement bearings if necessary.

(1) Remove differential side bearings from differential case.

(2) Remove factory installed shims from differential case.

(3) Install ring gear on differential case and tighten bolts to specification.

(4) Install dummy side bearings D-348 on differential case.

(5) Install differential case in axle housing.

(6) Install the marked bearing caps in their correct positions. Install and snug the bolts (Fig. 95).

Fig. 95 Tighten Bolts Holding Bearing Caps

1 - BEARING CAP
2 - AXLE HOUSING
3 - DIFFERENTIAL CASE

(7) Using a dead-blow type mallet, seat the differential dummy bearings to each side of the axle housing (Fig. 96) and (Fig. 97).

Fig. 96 Seat Pinion Gear Side Differential Dummy Side Bearing

1 - MALLET
2 - AXLE HOUSING
3 - DIFFERENTIAL CASE

(8) Thread guide stud C-3288-B into rear cover bolt hole below ring gear (Fig. 98).

(9) Attach a dial indicator C-3339 to guide stud.

Position the dial indicator plunger on a flat surface between the ring gear bolt heads (Fig. 98).

(10) Push and hold differential case to pinion gear side of axle housing (Fig. 99).

(11) Zero dial indicator face to pointer (Fig. 99).

Fig. 97 Seat Ring Gear Side Differential Dummy Side Bearing

1 - AXLE HOUSING
2 - MALLET
3 - DIFFERENTIAL CASE

Fig. 98 Differential Side play Measurement

1 - DIFFERENTIAL CASE
2 - AXLE HOUSING
3 - SPECIAL TOOL C-3288-B
4 - SPECIAL TOOL C-3339

(12) Push and hold differential case to ring gear side of the axle housing (Fig. 100).

(13) Record dial indicator reading (Fig. 100).

(14) Add 0.008 in. (0.2 mm) to the zero end play total. This new total represents the thickness of shims to compress, or preload the new bearings when the differential is installed.

Fig. 99 Hold Differential Case and Zero Dial Indicator

1 - FORCE DIFFERENTIAL CASE TO PINION GEAR SIDE
2 - SPECIAL TOOL C-3288-B
3 - SPECIAL TOOL C-3339
4 - ZERO DIAL INDICATOR FACE

Fig. 100 Hold Differential Case and Read Dial Indicator

1 - READ DIAL INDICATOR
2 - FORCE DIFFERENTIAL CASE TO RING GEAR SIDE
3 - AXLE HOUSING

(15) Rotate dial indicator out of the way on the guide stud.

(16) Remove differential case and dummy bearings from axle housing.

(17) Install the pinion in the axle housing. Install the pinion yoke and establish the correct pinion rotating torque.

(18) Install differential case and dummy bearings D-348 in axle housing (without shims), install bearing caps and tighten bolts snug.

(19) Seat ring gear side dummy bearing (Fig. 97).

(20) Position the dial indicator plunger on a flat surface between the ring gear bolt heads. (Fig. 98).

(21) Push and hold differential case toward pinion gear (Fig. 101).

(22) Zero dial indicator face to pointer (Fig. 101).

Fig. 101 Hold Differential Case and Zero Dial Indicator

1 - ZERO DIAL INDICATOR FACE
2 - FORCE DIFFERENTIAL CASE TO PINION GEAR SIDE
3 - PINION GEAR
4 - AXLE HOUSING
5 - DIFFERENTIAL CASE

(23) Push and hold differential case to ring gear side of the axle housing (Fig. 102).

(24) Record dial indicator reading (Fig. 102).

Fig. 102 Hold Differential Case and Read Dial Indicator

1 - READ DIAL INDICATOR
2 - FORCE DIFFERENTIAL CASE TO RING GEAR SIDE
3 - PINION GEAR
4 - AXLE HOUSING
5 - DIFFERENTIAL CASE

(25) Subtract 0.002 in. (0.05 mm) from the dial indicator reading to compensate for backlash between ring and pinion gears. This total is the thickness shim required to achieve proper backlash.

(26) Subtract the backlash shim thickness from the total preload shim thickness. The remainder is the shim thickness required on the pinion side of the axle housing.

(27) Rotate dial indicator out of the way on guide stud.

(28) Remove differential case and dummy bearings from axle housing.

(29) Install side bearing shims on differential case hubs.

(30) Install side bearings and cups on differential case.

(31) Install spreader W-129-B, utilizing some items from Adapter Set 6987, on axle housing and spread axle opening enough to receive differential case.

(32) Install differential case in axle housing.

(33) Remove spreader from axle housing.

(34) Rotate the differential case several times to seat the side bearings.

(35) Position the indicator plunger against a ring gear tooth (Fig. 103).

(36) Push and hold ring gear upward while not allowing the pinion gear to rotate.

(37) Zero dial indicator face to pointer.

(38) Push and hold ring gear downward while not allowing the pinion gear to rotate. Dial indicator reading should be between 0.12 mm (0.005 in.) and 0.20 mm (0.008 in.). If backlash is not within specifications transfer the necessary amount of shim thickness from one side of the axle housing to the other (Fig. 104).

(39) Verify differential case and ring gear runout by measuring ring to pinion gear backlash at eight locations around the ring gear. Readings should not vary more than 0.05 mm (0.002 in.). If readings vary more than specified, the ring gear or the differential case is defective.

After the proper backlash is achieved, perform Gear Contact Pattern Analysis procedure.