Differential Rebuild - Rear

Complete disassembly, inspection, rebuild and reassembly of the rear electric drive unit differential, including bearing replacement, gear inspection, and component reconditioning.

Warnings

Tools required

Parts

• Rear differential bearing set × 1 — Use OEM specification
• Differential pinion seal × 1 — Use OEM specification
• Differential side seals × 2 — Use OEM specification
• Differential cover gasket or RTV sealant × 1 — Use OEM specification
• Pinion shim kit × 1 — Use OEM specification
• Ring gear bolts × 1 — Use OEM specification (one-time use)
• Differential crush sleeve or spacer × 1 — Use OEM specification
• Differential side bearing shims × 1 — Use OEM specification
• Pinion nut × 1 — Use OEM specification (one-time use)

Fluids

• 75W-90 GL-5 Gear Oil — 2 qt

Preparation

1. Verify high voltage system is isolated following manufacturer HV safety procedures and place safety lock in service mode
2. Raise vehicle on lift and support securely with supplemental jack stands rated for EV weight
3. Remove rear wheels and set aside
4. Disconnect any electronic sensors connected to rear drive unit
5. Place drain pan under rear differential and drain gear oil completely
6. Remove rear axle shafts from differential and secure out of work area
7. Support rear drive unit with transmission jack if removing entire assembly, or support differential housing if working in-vehicle
8. Clean exterior of differential housing thoroughly to prevent contamination during disassembly
9. Establish clean work area with parts washer and organize tools for differential setup procedures

Procedure

1. 1

   Remove differential cover and initial inspection
   Remove differential cover bolts in cross pattern. Carefully separate cover from housing using plastic pry tool if needed. Inspect drained oil for metal particles, which indicate wear patterns. Check cover for cracks or damage. Inspect ring and pinion gears visually for obvious damage, scoring, or unusual wear patterns before disassembly.
2. 2

   Mark and measure gear backlash
   Before disassembly, mount dial indicator against ring gear tooth. Measure and record backlash at four points around ring gear, rotating 90 degrees each time. Standard backlash is typically 0.005-0.009 inches but verify with service data. Mark carrier bearing caps and housing with punch marks to ensure correct reassembly orientation. Paint mark ring gear and pinion orientation.
3. 3

   Remove differential carrier assembly
   Remove carrier bearing cap bolts. Note position and thickness of any shims on each side of carrier. Use pry bars carefully to break carrier free from bearings. Lift carrier assembly with ring gear out of housing. Keep side bearing races and shims together with their respective sides - mark LEFT and RIGHT clearly.
4. 4

   Remove pinion gear assembly
   Mark pinion nut position relative to pinion shaft for reference. Hold pinion flange with holding tool and remove pinion nut (this is a one-time use nut). Use appropriate puller to remove pinion flange. Carefully tap pinion shaft out from rear of housing. Catch pinion gear as it comes free - note any shims behind pinion head bearing. Remove pinion oil seal and both pinion bearings from housing using bearing puller.
5. 5

   Disassemble carrier and ring gear
   Mount carrier assembly in soft-jaw vise. Remove ring gear bolts (these are one-time use fasteners). If ring gear is tight, use brass drift to carefully tap between ring gear and carrier to separate. Drive out differential pinion shaft roll pin. Remove pinion shaft, pinion gears, side gears, and thrust washers. Keep all components organized and labeled.
6. 6

   Remove bearings and inspect all components
   Use bearing splitter and press to remove carrier side bearings from carrier. Remove bearing races from housing using race puller or driver from backside. Thoroughly clean all components in parts washer. Inspect all gear teeth for pitting, scoring, excessive wear, or cracks. Inspect carrier for cracks or damage. Inspect bearing surfaces on all shafts for scoring. Check all thrust surfaces. Replace any components showing damage or excessive wear. Measure ring gear runout if reusing - must be under 0.003 inches.
7. 7

   Install new pinion bearings and determine pinion depth
   Press new pinion bearing races into housing, ensuring they seat completely. Install inner pinion bearing on pinion gear using press. This is critical: use pinion depth setting tool or use original shim thickness as starting point. Install pinion in housing with shim, outer bearing, and depth setting tools to measure pinion depth with dial indicator. Adjust shim thickness until correct pinion depth is achieved per service specifications. Record final shim thickness.
8. 8

   Install pinion with crush sleeve and set preload
   Install selected shim on pinion, then inner bearing. Install pinion into housing from rear. Install new crush sleeve on pinion shaft. Install outer pinion bearing, pinion flange, and new pinion nut. Hold flange and tighten nut gradually while checking pinion rotating torque with inch-pound torque wrench. Target preload is typically 15-25 inch-pounds for new bearings. Crush sleeve must be compressed properly - if nut bottoms out before reaching preload, crush sleeve is incorrect and must be replaced. If preload is exceeded, entire assembly must be replaced and restarted.
9. 9

   Reassemble differential carrier
   Install side gears and thrust washers into carrier. Install pinion gears with thrust washers and pinion shaft. Verify all gears rotate smoothly. Align pinion shaft roll pin hole and install new roll pin. Position new or cleaned ring gear on carrier, aligning all bolt holes. Install new ring gear bolts with thread locker and tighten in star pattern to specification. Verify ring gear runout is within specification using dial indicator.
10. 10

    Install carrier side bearings
    Press new side bearings onto carrier using appropriate bearing driver and press. Ensure bearings are fully seated against carrier shoulders. Install bearing races in housing if not already installed, ensuring they are fully seated.
11. 11

    Set carrier bearing preload and backlash
    This is the most critical step. Install carrier assembly into housing without shims initially to measure clearance. Use feeler gauges to measure gap on each side between bearing race and housing. Calculate shim thickness required: add shim thickness equal to clearance plus additional shims for preload (typically 0.005-0.010 inch total). Install shims on each side - add or remove shims from sides to achieve both proper backlash (0.005-0.009 inch typical) and proper bearing preload. More shim on ring gear side decreases backlash. Install bearing caps in correct orientation and tighten bolts. Check backlash with dial indicator at multiple points. Adjust shims as needed.
12. 12

    Verify gear contact pattern
    Apply gear marking compound to several ring gear teeth. Rotate pinion in both directions under slight load to create contact pattern. Inspect pattern - it should be centered on tooth face. If pattern is too high, decrease pinion depth (add shim). If too low, increase pinion depth (remove shim). If pattern favors toe, decrease backlash. If pattern favors heel, increase backlash. Adjust and recheck until proper pattern is achieved. This may require multiple iterations.
13. 13

    Install new seals
    Install new pinion seal using seal driver, ensuring it seats squarely and to proper depth. Install new differential side seals into axle tube openings if applicable. Coat seal lips with gear oil before installation.
14. 14

    Final assembly and fill
    Clean differential cover and housing mating surface thoroughly. Apply new gasket or RTV sealant per manufacturer specification. Install differential cover and tighten bolts in cross pattern. Fill differential with 2.0 quarts of 75W-90 GL-5 gear oil through fill plug. Oil level should reach bottom of fill plug opening. Install and tighten fill plug.
15. 15

    Reinstall drive components and test
    Reinstall rear axle shafts into differential with new seals or o-rings as required. Reconnect all electrical sensors and verify connections are secure. Reinstall wheels and lower vehicle. Remove HV safety locks and restore vehicle to normal operation mode. Test drive vehicle at low speed initially, listening for any unusual noise. Gradually increase speed and load while monitoring for vibration or noise. Return and recheck gear oil level after test drive.

Reassembly

1. Bearing preload and gear backlash settings are critical - verify multiple times during assembly
2. All fasteners marked as one-time use (pinion nut, ring gear bolts) must be replaced with new parts
3. Take time to achieve proper gear contact pattern - rushing this step will result in premature failure
4. Cleanliness is essential - any contamination in differential will cause rapid bearing failure

Verification

• Verify pinion rotating torque is within specification (typically 15-25 inch-pounds for new bearings)
• Verify ring gear backlash is within specification at all measurement points (typically 0.005-0.009 inches)
• Verify gear tooth contact pattern is centered and appropriate for both drive and coast sides
• Check for gear oil leaks around cover, pinion seal, and axle seals after installation
• Test drive vehicle and verify smooth operation with no whining, howling, or vibration from rear axle
• Recheck fluid level after test drive - top off if necessary
• Monitor differential operation for first 500 miles and recheck fluid level and inspect for leaks

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