Differential Service

Replace the rear differential fluid and inspect the differential cover gasket to maintain proper lubrication and prevent gear wear.

Warnings

Tools required

Parts

• Differential cover gasket (if reusing cover) × 1 — ACDelco 88953521 or equivalent
• RTV silicone sealant × 1 — GM 12378521
• Shop towels × 1 — Use OEM specification

Fluids

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

Preparation

1. Park vehicle on level surface and engage parking brake
2. Verify vehicle has cooled for at least 30 minutes if recently driven
3. Check RPO codes on driver door jamb label to confirm differential type (GT4=3.42 ratio, GT5=3.23 ratio, GU6=3.08 ratio)
4. Gather all tools, replacement fluid, and RTV sealant before beginning
5. Position drain pan under rear differential

Procedure

1. 1

   Access the differential cover
   Locate the rear differential cover at the center of the rear axle. Clean the exterior of the cover and surrounding area with brake cleaner to prevent contamination when opened.
2. 2

   Remove differential cover bolts
   Using a 3/8" drive ratchet and appropriate socket, loosen all cover bolts in a crisscross pattern. Leave the top two bolts partially threaded to prevent the cover from falling when fluid drains.
   Torque spec

   Cover Bolts42 Nm (31 lb-ft)
3. 3

   Drain differential fluid
   Position drain pan directly beneath the differential cover. Carefully remove the bottom bolts first, allowing fluid to drain. Once flow slows, remove remaining bolts and carefully pry the cover away from the housing using a scraper. Allow all fluid to drain completely (approximately 2 quarts).
   ⚠Fluid may drain quickly once cover is loosened. Ensure drain pan is properly positioned to avoid spills.
4. 4

   Inspect differential internals
   With cover removed, visually inspect the ring and pinion gears for abnormal wear, scoring, or metal debris. Check the magnetic drain plug (if equipped on cover) for excessive metallic particles. Small amounts of fine metallic paste are normal; large chunks or excessive debris indicate potential internal damage requiring further inspection.
5. 5

   Clean differential cover and housing
   Remove all old gasket material and RTV sealant from both the differential cover and housing mating surface using a scraper. Be careful not to gouge the aluminum surfaces. Clean both surfaces thoroughly with brake cleaner and wipe dry with lint-free shop towels. Ensure no debris falls into the differential housing.
   ⚠Do not allow gasket material or debris to fall into the differential housing as this can damage gears and bearings.
6. 6

   Apply RTV sealant to cover
   Apply a continuous 3-4mm bead of RTV silicone sealant (GM 12378521 or equivalent) to the differential cover mating surface. Run the bead around the inside of the bolt holes. Work quickly as RTV begins to skin over within 10 minutes.
   ℹ️GM specifies RTV sealant instead of a pre-formed gasket for the 2014-2018 Silverado rear differential. Do not use both RTV and a gasket together.
7. 7

   Install differential cover
   Carefully position the differential cover onto the housing, aligning all bolt holes. Install all cover bolts hand-tight. Using a torque wrench, tighten bolts in a crisscross star pattern to specification to ensure even gasket compression.
   ℹ️Cover must be installed and bolts torqued within 10 minutes of RTV application for proper seal.
   Torque spec

   Cover Bolts42 Nm (31 lb-ft)
8. 8

   Allow RTV to cure
   Wait at least 10 minutes before filling with gear oil to allow RTV sealant to set. For best results, allow 1 hour cure time before driving, or overnight for full cure.
9. 9

   Refill differential with gear oil
   Locate the fill plug on the front or side of the differential housing. Remove the fill plug. Using a fluid pump or squeeze bottle, add ACDelco 75W-90 synthetic gear oil through the fill hole until fluid begins to seep out of the fill hole (approximately 2.0 quarts). If vehicle is equipped with limited slip differential (RPO GT4 or GT5), add the appropriate GM limited slip additive per manufacturer specifications.
   ℹ️Fill differential until fluid reaches the bottom of the fill plug hole. Overfilling can cause seal damage and leaks.
   Torque spec

   Fill Plug51 Nm (38 lb-ft)
10. 10

    Install fill plug
    Clean the fill plug threads and reinstall. Torque the fill plug to specification using a torque wrench.
    Torque spec

    Fill Plug51 Nm (38 lb-ft)
11. 11

    Clean up and dispose of waste
    Wipe down the differential housing and surrounding area to remove any spilled gear oil. Properly dispose of used differential fluid at a recycling center or auto parts store that accepts used oil.

Reassembly

1. Ensure all cover bolts are torqued to specification in a crisscross pattern
2. Verify fill plug is tight and properly torqued
3. Clean any gear oil residue from the differential housing exterior
4. Allow RTV sealant to cure for at least 10 minutes before driving, 1 hour recommended for full seal

Verification

• Start engine and allow to idle for 1-2 minutes, then shift through all gears
• Inspect differential cover for any signs of leakage around the gasket seam
• Test drive vehicle for 5-10 miles, checking for unusual noises from the rear differential
• Re-inspect differential cover for leaks after test drive
• Check fluid level at fill plug after 50-100 miles of driving and top off if necessary

Related trouble codes on this vehicle

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