Differential Rebuild - Rear

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

Warnings

Tools required

Parts

• Differential bearing overhaul kit × 1 — Use OEM specification for 9.75-inch rear axle
• Pinion seal × 1 — Use OEM specification
• Axle seals × 2 — Use OEM specification
• Ring and pinion gear set (if replacing) × 1 — Use OEM specification for axle ratio
• Crush sleeve × 1 — Use OEM specification
• Pinion nut × 1 — Use OEM specification
• Differential cover gasket or RTV sealant × 1 — Motorcraft TA-357 or equivalent
• Gear marking compound × 1 — Use OEM specification
• Shim kit for pinion depth adjustment × 1 — Use OEM specification
• Brake cleaner × 2 — Use OEM specification
• Shop towels × 1 — Use OEM specification

Fluids

• Motorcraft 75W-140 Synthetic Gear Oil — 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 securely on jack stands at frame rails
4. Remove rear wheels and set aside
5. Place drain pan under differential
6. Mark driveshaft and pinion flange orientation for reassembly alignment
7. Take photos of all components before disassembly for reference

Procedure

1. 1

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

   Drain Plug47 Nm (35 lb-ft)

   Cover Bolts39 Nm (29 lb-ft)
2. 2

   Remove driveshaft
   Remove four driveshaft U-joint strap bolts at pinion flange. Support driveshaft and carefully lower it down, sliding yoke out of transmission. Use tape or plug to prevent transmission fluid loss. Set driveshaft aside in safe location maintaining proper orientation marks.
   ⚠Do not allow driveshaft to hang unsupported as this can damage universal joints.
   Torque spec

   Driveshaft U-Joint Straps20 Nm (15 lb-ft)
3. 3

   Mark and measure pinion
   Using paint or marker, mark pinion flange, pinion nut, and pinion shaft for rotational alignment reference. Count and record exact number of threads showing above pinion nut. Using inch-pound torque wrench and appropriate socket, measure and record pinion rotating torque (should be 15-25 in-lbs for used bearings). This baseline is critical for proper reassembly preload.
4. 4

   Remove pinion flange and seal
   Hold pinion flange with holding tool or large pipe wrench on flange. Remove pinion nut using breaker bar and socket. Use appropriate puller to remove pinion flange from pinion shaft. Once flange is removed, carefully pry out pinion seal using seal puller or screwdriver. Note depth of seal installation for new seal installation.
   ⚠Pinion nut may require significant force to remove. Ensure proper tool engagement to avoid rounding nut.
5. 5

   Remove differential assembly
   Using paint marker, mark bearing caps with 'L' and 'R' and indicate front orientation. Remove bearing cap bolts and carefully remove bearing caps. Note: caps are machined matched sets and must return to original positions. If using differential spreader, install and carefully spread housing per tool specifications (maximum 0.015 inches). Using pry bars on both sides, carefully pry differential case assembly upward and out of housing. Remove and keep side bearing adjusters with their respective sides, marking orientation.
   ⚠️Do not over-spread differential housing beyond tool specifications or permanent housing damage will occur.
   ⚠Differential case assembly is heavy (approximately 30-40 lbs). Use proper lifting technique or assistance.
6. 6

   Remove pinion assembly
   From front of differential housing, tap pinion shaft rearward using soft-faced mallet or brass punch. Remove pinion shaft, front pinion bearing, collapsible spacer/crush sleeve, rear pinion bearing, and any shims from housing. Keep all shims organized and labeled by location. Using brass drift and hammer, carefully drive out front and rear pinion bearing races from housing. Inspect housing for scoring, pitting, or cracks.
7. 7

   Disassemble differential case
   Mount differential case in padded vise. If reusing ring gear, mark ring gear to case orientation. Remove ring gear bolts (typically left-hand thread). If bolts are tight, use penetrating oil and impact wrench. Tap ring gear off case using soft-faced hammer if necessary. Drive out differential pinion shaft roll pin using appropriate punch. Remove pinion shaft, spider gears, and side gears. Keep all components organized. Using bearing puller or press, remove side bearings from case. Mark bearings left and right if reusing.
   ⚠Ring gear bolts typically have left-hand threads. Turn clockwise to loosen.
8. 8

   Inspect all components
   Thoroughly clean all components with brake cleaner and compressed air. Inspect ring and pinion gear teeth for scoring, pitting, chipping, or excessive wear. Check all bearing surfaces for pitting, galling, or discoloration. Inspect differential case for cracks, especially around bearing bores and bolt holes. Check housing for cracks, scoring in bearing bore areas, and thread damage. Replace any components showing wear or damage. For preventive rebuild, minimum replacement includes all bearings, seals, crush sleeve, and pinion nut.
9. 9

   Install new pinion bearing races
   Using bearing race driver and hammer, install new front and rear pinion bearing races into differential housing. Drive races in squarely until fully seated against housing shoulders. Verify seating by attempting to insert feeler gauge between race and shoulder - no gap should exist. Clean race surfaces thoroughly with brake cleaner.
10. 10

    Determine pinion depth
    Install pinion depth setting gauge tools per manufacturer instructions. This typically involves installing gauge block in differential bearing bores and measuring pinion depth. If reusing original ring and pinion, use original shim thickness as starting point. If installing new gear set, use gear set markings and gauge readings to determine correct shim thickness. Most Ford 9.75-inch differentials use shims behind rear pinion bearing. Add or remove shim thickness per gear set markings (typically +/- values etched on pinion head).
    ℹ️Pinion depth is critical for proper gear contact pattern. Take time to measure accurately.
11. 11

    Assemble and install pinion
    Press rear pinion bearing onto pinion shaft with correct shim pack behind bearing. Lubricate front and rear bearings with gear oil. Install pinion assembly into housing from front. Install new collapsible spacer/crush sleeve onto pinion shaft. Install front pinion bearing. Lubricate pinion seal lip with gear oil and install new seal using seal driver to proper depth. Install pinion flange, aligning reference marks if reusing components. Install NEW pinion nut finger tight.
12. 12

    Set pinion bearing preload
    Using holding tool on pinion flange, tighten pinion nut gradually while checking pinion rotating torque frequently with inch-pound torque wrench. Target preload for new bearings is 16-29 in-lbs rotating torque. Tighten nut slowly - crush sleeve is collapsing and cannot be loosened. If preload is exceeded, pinion nut, crush sleeve, and potentially bearings must be replaced and process restarted. Once correct preload is achieved, verify pinion flange has no end play.
    ⚠️Never loosen pinion nut to reduce preload. This destroys crush sleeve integrity. If preload is exceeded, complete disassembly and new parts are required.
    ⚠Check preload every 1/4 turn of nut near final torque. Preload can increase rapidly.
13. 13

    Assemble differential case
    If installing new ring gear, clean ring gear and case mating surfaces thoroughly. Install ring gear on case, aligning bolt holes. Apply thread locker to ring gear bolts. Install and tighten ring gear bolts in crisscross pattern to specification (typically 100-120 ft-lbs, verify with service manual). Install side gears and spider gears into case with proper thrust washers. Install pinion shaft through case and gears. Align roll pin hole and install new roll pin, ensuring it is fully seated below case surface.
14. 14

    Install side bearings and case
    Press or drive new side bearings onto differential case, ensuring proper seating. Install side bearing adjuster nuts onto case, threading approximately same depth as removed. Lubricate side bearings with gear oil. Carefully install differential case assembly into housing, seating bearings into races. If using spreader, spread housing slightly to ease installation. Install bearing caps in original positions per orientation marks. Install cap bolts finger tight.
15. 15

    Set backlash and side bearing preload
    Using side bearing adjuster tool, tighten bearing adjusters evenly on both sides until differential case has zero end play. Mount dial indicator to housing with plunger on ring gear tooth at 90 degrees to rotation. Rock ring gear back and forth while reading backlash. Specification is typically 0.005-0.009 inches (0.127-0.229 mm). Adjust by turning one adjuster in and opposite adjuster out by equal amounts. Once backlash is correct, tighten each adjuster an additional 1-2 notches to set side bearing preload. Verify backlash remains in specification. Tighten bearing cap bolts to specification (typically 55-75 ft-lbs, verify with service manual).
    ℹ️Backlash adjustment requires patience. Make small adjustments and recheck frequently.
16. 16

    Check gear contact pattern
    Apply thin coat of gear marking compound to 8-10 ring gear teeth in several locations. Rotate pinion while applying resistance to ring gear to establish contact pattern. Examine pattern on drive and coast sides of teeth. Proper pattern should be centered on tooth face, slightly favoring toe on drive side. If pattern is incorrect, adjust pinion depth (requires disassembly) or backlash as needed. Repeat until satisfactory pattern is achieved on both drive and coast sides.
    ℹ️Gear pattern interpretation requires experience. Consult service manual diagrams for acceptable patterns.
17. 17

    Install driveshaft and refill differential
    Clean differential cover and housing mating surfaces thoroughly. Apply RTV sealant per manufacturer specifications (typically 1/8-inch bead around cover perimeter). Install cover and bolts, tightening in crisscross pattern. Slide driveshaft yoke into transmission extension housing. Align driveshaft to pinion flange using reference marks. Install U-joint straps and bolts, tightening evenly. Remove fill plug and fill differential with Motorcraft 75W-140 Synthetic Gear Oil until level reaches bottom of fill hole. Install fill plug with new washer.
    Torque spec

    Cover Bolts39 Nm (29 lb-ft)

    Driveshaft U-Joint Straps20 Nm (15 lb-ft)

    Fill Plug47 Nm (35 lb-ft)

Reassembly

1. Allow RTV sealant to cure per manufacturer specifications before test driving (typically 1 hour minimum)
2. Install rear wheels and tighten lug nuts in star pattern to specification
3. Lower vehicle to ground and perform final lug nut torque verification
4. Test drive vehicle to verify proper operation and listen for abnormal noises

Verification

• Check for fluid leaks around pinion seal, axle seals, and differential cover after initial test drive
• Verify no abnormal noises during acceleration, deceleration, and turning
• Recheck differential fluid level after test drive and top off if necessary
• After 50-100 miles, recheck all fastener torques and inspect for leaks
• Monitor differential operation for first 500 miles during break-in period

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