Differential Rebuild - Rear

Complete disassembly, inspection, and rebuild of the rear differential assembly including bearing replacement, gear setup, and proper backlash adjustment.

Warnings

Tools required

Parts

• Rear differential master rebuild kit with bearings × 1 — Use OEM specification for your axle ratio
• Pinion seal × 1 — Use OEM specification
• Pinion nut × 1 — One-time use, replace during rebuild
• Differential cover gasket or RTV sealant × 1 — Motorcraft TA-30 or equivalent
• Pinion shim kit × 1 — Required for proper pinion depth setting
• Carrier shim kit × 1 — Required for proper backlash adjustment
• Ring and pinion gear set (if replacing) × 1 — Must match existing gear ratio or reprogram PCM
• Gear marking compound × 1 — For pattern verification
• Shop rags × 1 — Standard
• Brake cleaner × 2 — For cleaning components

Fluids

• Motorcraft 75W-140 Synthetic Rear Differential Fluid — 2.5 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Loosen rear wheel lug nuts while vehicle is on ground
3. Raise rear of vehicle and support on jack stands at frame rails behind rear axle
4. Remove both rear wheels
5. Place drain pan under differential
6. Mark driveshaft and pinion flange relationship for proper reinstallation alignment
7. Take photos of any axle vent line routing for reference
8. Clean exterior of differential housing to prevent contamination during disassembly

Procedure

1. 1

   Drain differential and remove cover
   If equipped with drain plug, remove drain plug and drain fluid completely into pan. If no drain plug, remove differential cover bolts in crisscross pattern starting from top, leaving bottom bolts partially engaged. Carefully pry cover loose and allow fluid to drain. Once drained, remove remaining cover bolts and cover. Clean all old gasket material or RTV from housing and cover using scraper.
   Torque spec

   Drain Plug51 Nm (38 lb-ft)

   Cover Bolts42 Nm (31 lb-ft)
2. 2

   Remove driveshaft
   Remove four driveshaft bolts at pinion flange. Support driveshaft and carefully slide it rearward to separate from pinion flange. Mark U-joint strap orientation if applicable. Secure driveshaft out of work area. Install shop rag into pinion flange opening to prevent fluid leakage.
   Torque spec

   Driveshaft Bolts94 Nm (69 lb-ft)
3. 3

   Remove axle shafts
   Remove brake calipers and rotors to access axle nuts. Remove axle nuts (if equipped with cotter pins, remove pins first). Remove wheel speed sensor connectors and mounting bolts. Support axle shafts and remove CV joint bolts connecting shafts to differential side gears. Carefully pull axle shafts outward and secure away from differential housing.
   Torque spec

   Axle Nut250 Nm (184 lb-ft)

   CV Joint Bolts76 Nm (56 lb-ft)
4. 4

   Mark and measure carrier bearing preload
   Using dial indicator, measure and record ring gear backlash at multiple teeth positions. Mark carrier bearing cap orientation with punch marks - caps are matched and must be reinstalled in original position. Measure and record carrier bearing preload using inch-pound torque wrench on ring gear bolt (rotate continuously and record rotating torque). Record all measurements for comparison during reassembly.
5. 5

   Remove carrier assembly
   Remove carrier bearing cap bolts. Carefully pry bearing caps off using pry bars - caps may be tight. Note any shims behind bearing caps and keep with correct side. Lift carrier assembly with ring gear out of housing. Place on clean work surface. Inspect ring gear teeth for wear patterns and damage.
   ⚠Carrier bearing caps are machined matched to the housing. Mark orientation clearly and never interchange left and right caps.
6. 6

   Disassemble carrier and remove bearings
   Install carrier in case spreader tool. Spread case only enough to remove ring gear (maximum 0.015 inches spread). Remove ring gear bolts and tap ring gear off carrier using soft mallet. Using bearing puller or press, remove carrier bearings from both sides of carrier. Mark which bearing came from which side. Remove differential cross shaft lock bolt, cross shaft, side gears, and pinion gears. Inspect all components for wear.
7. 7

   Remove pinion gear assembly
   Using pinion holding tool to prevent rotation, remove pinion nut (this is a one-time use nut, discard). Mark pinion flange position on pinion shaft. Using puller, remove pinion flange. Remove pinion seal and discard. Carefully tap pinion shaft out from front of housing, catching rear pinion bearing and shims. Remove front pinion bearing from housing using bearing puller. Remove pinion bearing races from housing using race puller or brass punch.
8. 8

   Clean and inspect all components
   Thoroughly clean all gears, carrier, housing, and bearing surfaces with brake cleaner. Inspect ring and pinion gear teeth for scoring, pitting, or excessive wear. Inspect carrier for cracks. Inspect housing bearing bores for scoring. Inspect pinion splines for damage. Replace ring and pinion set if any gear damage is present - these are matched sets. Inspect all bearing surfaces for roughness or pitting.
9. 9

   Install new pinion bearing races
   Using bearing race driver or press, install new front and rear pinion bearing races into housing. Ensure races are fully seated and square in bores. Install new front pinion bearing onto pinion shaft using press (if not pre-installed). Install rear pinion bearing onto pinion shaft using press.
10. 10

    Set pinion depth
    Install pinion depth setting shims (start with shims removed during disassembly unless changing gear set). Install pinion assembly into housing from rear with rear bearing, collapsible spacer or solid spacer, and front bearing. Install pinion flange and new pinion nut. Tighten pinion nut to achieve proper pinion bearing preload: 10-20 inch-pounds for new bearings, 5-10 inch-pounds for used bearings (rotating torque measured with inch-pound torque wrench). DO NOT overtighten - collapsible spacer cannot be reused if crushed too far.
    ⚠️Pinion bearing preload is critical. Overtightening collapses the spacer and requires complete disassembly and new spacer. Approach target preload slowly.
11. 11

    Check and adjust pinion depth with marking compound
    Temporarily install carrier assembly without shims. Apply gear marking compound to 3-4 ring gear teeth. Rotate pinion in both directions while applying resistance to ring gear. Check contact pattern on teeth. Pattern should be centered on tooth face. If pattern is toward heel (large end), increase pinion shim thickness. If toward toe (small end), decrease shim thickness. Each 0.003 inch shim change moves pattern approximately half a tooth width. Repeat until pattern is correct.
12. 12

    Reassemble carrier with new bearings
    Install new side gears, pinion gears, and cross shaft into carrier. Install cross shaft lock bolt finger tight. Using press or bearing installation tool, install new carrier bearings onto carrier (one on each side). If reusing ring gear, clean old thread locker from bolts and apply new thread locker. Install ring gear onto carrier and torque ring gear bolts in star pattern to manufacturer specification (not provided in torque list - typically 100-120 lb-ft, verify with service manual).
13. 13

    Install carrier and set backlash
    Install carrier bearing shims (start with original shim thickness). Install carrier assembly into housing. Install bearing caps in original orientation - match punch marks. Tighten bearing cap bolts evenly. Using dial indicator on ring gear tooth, measure backlash. Specification is typically 0.005-0.009 inches. To decrease backlash, move shim thickness from right side to left side (same total thickness). To increase backlash, move shim from left to right. Adjust until backlash is within specification.
    ⚠Maintain constant total shim thickness to preserve carrier bearing preload while adjusting backlash. Only transfer shims between sides.
14. 14

    Verify final gear pattern and backlash
    Apply fresh gear marking compound to multiple ring gear teeth. Rotate pinion in both directions under load. Check pattern on drive and coast sides of teeth - pattern should be centered with proper oval shape. Measure backlash at 4 points around ring gear - variation should not exceed 0.002 inches. Verify carrier bearing preload matches original specification. Make final adjustments if needed.
15. 15

    Install new pinion seal
    Remove pinion flange and clean seal bore. Coat outer edge of new pinion seal with RTV sealant. Using seal driver, install new pinion seal into housing - seal should be flush with housing face. Coat seal lip with differential fluid. Install pinion flange aligned with original marks. Install new pinion nut and tighten to achieve proper bearing preload specification from step 10. Verify preload has not changed after final tightening.
    ℹ️Pinion nut torque is not the specification - bearing preload (rotating torque) is the critical measurement. Final pinion nut torque will vary.
16. 16

    Reinstall axle shafts and driveshaft
    Install axle shafts into differential side gears. Install CV joint bolts and torque to specification. Install wheel speed sensors. Install new axle nuts and torque to specification, then install new cotter pins or stake nuts as applicable. Align driveshaft to pinion flange using reference marks. Install driveshaft bolts and torque to specification in star pattern.
    Torque spec

    CV Joint Bolts76 Nm (56 lb-ft)

    Axle Nut250 Nm (184 lb-ft)

    Driveshaft Bolts94 Nm (69 lb-ft)
17. 17

    Install differential cover and fill
    Clean cover and housing mating surfaces thoroughly. Apply continuous 1/8 inch bead of RTV sealant to cover or install new gasket per manufacturer specification. Install cover and torque bolts in crisscross pattern to specification. Allow RTV to cure per manufacturer instructions (typically 1 hour). Remove fill plug and fill differential with Motorcraft 75W-140 synthetic gear oil until fluid reaches bottom of fill hole (approximately 2.0-2.5 quarts). Install fill plug with new washer if equipped and torque to specification.
    Torque spec

    Cover Bolts42 Nm (31 lb-ft)

    Fill Plug51 Nm (38 lb-ft)
18. 18

    Reinstall wheels and lower vehicle
    Install brake rotors and calipers. Install wheels and hand-tighten lug nuts in star pattern. Lower vehicle until tires just contact ground. Torque wheel lug nuts to specification in star pattern. Fully lower vehicle and remove jack stands.
    Torque spec

    Wheel Lug Nuts140 Nm (103 lb-ft)

Reassembly

1. Ensure all torque specifications were followed in correct sequence
2. Verify no tools or parts were left in differential housing
3. Check for any fluid leaks around pinion seal and differential cover
4. Ensure all electrical connectors for wheel speed sensors are properly connected

Verification

• Start engine and verify no unusual noises from differential
• Test drive vehicle at low speed (under 25 mph) and verify smooth operation in both forward and reverse
• Listen for gear whine, howling, or clunking which indicates improper setup
• Check for leaks around pinion seal and differential cover after test drive
• Recheck differential fluid level after test drive - top off if needed
• Perform final road test at highway speeds to verify quiet operation under load and deceleration
• Inspect fluid level and check for leaks again after 500 miles of driving
• If any abnormal noise is present, pattern must be rechecked and adjustments made

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