This procedure replaces the pinion seal on the rear differential to stop fluid leaks at the driveshaft connection point.

Warnings

Tools required

Parts

• Pinion seal × 1 — Use OEM specification
• Pinion nut (if reusing shows wear) × 1 — Use OEM specification
• RTV silicone sealant × 1 — High-temperature rated

Fluids

• ACDelco 75W-90 Synthetic Gear Oil — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Place wheel chocks at front wheels
3. Raise rear of vehicle and support securely on jack stands at frame rails
4. Allow differential to cool completely if recently driven
5. Position drain pan under differential

Procedure

1. 1

   Mark driveshaft and pinion flange alignment
   Use white paint marker to mark the driveshaft yoke and pinion flange relationship. This ensures proper reinstallation alignment and prevents driveline vibration. Mark both sides of the connection clearly.
2. 2

   Remove driveshaft
   Remove the four bolts connecting the driveshaft U-joint straps to the pinion flange. Support the driveshaft and carefully lower it, then slide it rearward out of the transmission. Plug the transmission extension housing with a rag to prevent fluid leakage.
   Torque spec

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

   Measure pinion rotating torque
   Using an inch-pound torque wrench on the pinion nut, measure and record the torque required to rotate the pinion (rotational drag). This baseline reading is critical for setting proper bearing preload during reassembly. Typical reading is 3-5 inch-pounds on used bearings.
   ℹ️This measurement is essential. Write down the value - you will need to match or slightly exceed it during reassembly.
4. 4

   Mark pinion nut position
   Using the paint marker, mark a line across the pinion nut and pinion shaft. This provides a visual reference for the nut's original position and helps prevent over-tightening during reassembly.
5. 5

   Remove pinion nut
   Hold the pinion flange securely with the holding tool or pipe wrench. Remove the pinion nut using a socket. Keep the nut for inspection - replace if threads show damage or deformation.
   ⚠The flange must be held firmly to prevent pinion shaft rotation which could damage bearings.
6. 6

   Remove pinion flange
   Using a suitable puller or by tapping with a rubber mallet while supporting the flange, remove the pinion flange from the pinion shaft. The flange is typically a tight fit. Note the orientation and any shims or spacers present.
7. 7

   Remove old pinion seal
   Using a seal puller or pry tool, carefully remove the old pinion seal from the differential housing. Work carefully to avoid scratching or damaging the seal bore in the housing. Clean the seal bore thoroughly with brake cleaner and inspect for damage or scoring.
8. 8

   Install new pinion seal
   Lightly coat the outer diameter of the new seal with RTV silicone. Coat the seal lip with clean gear oil. Using a seal driver or appropriately-sized socket, drive the seal squarely into the bore until it seats flush with the housing face. Ensure the seal is not cocked or damaged during installation.
   ⚠Seal must be driven in straight and square. A cocked seal will leak immediately.
9. 9

   Reinstall pinion flange
   Clean the pinion shaft splines and flange splines. Apply a light coat of gear oil to the pinion shaft seal surface. Carefully slide the pinion flange onto the shaft, aligning any marks made during disassembly. Ensure the flange seats fully onto the shaft.
10. 10

    Install and torque pinion nut
    Install the pinion nut (new or inspected original). While holding the flange, tighten the nut gradually. Check rotating torque frequently with inch-pound torque wrench. Tighten the nut until rotating torque equals or slightly exceeds (1-2 inch-pounds higher) the original measurement from step 3. The alignment marks should be close to their original position.
    ⚠️Do not overtighten. Excessive preload will destroy pinion bearings. If you exceed desired preload, the pinion nut must be replaced and the procedure restarted.
    ℹ️Typical final torque is 160-180 lb-ft, but you must achieve correct bearing preload, not a specific torque value. Preload is critical.
11. 11

    Reinstall driveshaft
    Remove the rag from the transmission extension housing. Slide the driveshaft into the transmission, then align the U-joint straps with the pinion flange using your alignment marks. Install the four U-joint strap bolts and torque evenly in a criss-cross pattern.
    Torque spec

    Driveshaft U-Joint Straps20 Nm (15 lb-ft)
12. 12

    Refill differential
    Remove the differential fill plug (upper plug on cover or housing). Using a fluid pump, fill the differential with ACDelco 75W-90 Synthetic Gear Oil until fluid reaches the bottom of the fill hole. Install and tighten the fill plug. Total capacity is approximately 2 quarts.

Reassembly

1. Verify all bolts and connections are tight and properly torqued
2. Wipe down the differential housing and pinion area to enable leak detection
3. Lower vehicle from jack stands
4. Remove wheel chocks

Verification

• Start the engine and shift through all gears including reverse while stationary to circulate gear oil
• Test drive vehicle 10-15 miles, making several turns in each direction
• Re-inspect pinion seal area for any signs of leakage
• Check for unusual noises from differential during acceleration and deceleration
• Verify no driveline vibration (indicates proper driveshaft alignment)
• Recheck differential fluid level after test drive and top off if necessary

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