Differential Service

Drain and refill the rear differential with fresh 75W-90 synthetic gear oil, inspecting the gear oil condition and magnetic drain plug for metal debris.

Warnings

Tools required

Parts

• Differential drain plug gasket/washer × 1 — Use OEM specification
• Differential fill plug gasket/washer × 1 — Use OEM specification

Fluids

• 75W-90 synthetic gear oil — 2.75 qt

Preparation

1. Park vehicle on level ground and engage parking brake.
2. Place wheel chocks in front of front tires.
3. Raise rear of vehicle using floor jack at rear differential housing or rear subframe jack points.
4. Support vehicle securely on jack stands rated for vehicle weight, positioned at manufacturer-recommended lift points on rear subframe.
5. Verify vehicle is stable before working underneath.
6. Ensure rear differential has cooled to safe handling temperature if vehicle was recently driven.

Procedure

1. 1

   Locate differential drain and fill plugs
   Position yourself under the rear of the vehicle with a work light. Verify the differential design before proceeding. The 2008 Viper rear differential (Dana-type) is commonly a cover-service unit without a dedicated bottom drain plug; fluid is drained by removing the rear differential cover and refilled through a side fill plug located on the housing. Confirm the presence and location of any drain and fill plugs against the factory service manual for this specific vehicle before beginning. Clean the area around both plugs with a wire brush or shop rag to prevent contamination when plugs are removed.
2. 2

   Remove fill plug first
   Using the appropriate metric socket, loosen and remove the fill plug from the side of the differential housing. This ensures you can refill the differential after draining; if the fill plug is seized, you do not want to discover this after draining the fluid. Set the fill plug aside and inspect the condition of the gasket/washer. Replace if damaged or compressed.
3. 3

   Position drain pan and remove drain plug
   If the differential is equipped with a bottom drain plug, position the oil drain pan directly beneath it, loosen the plug with the appropriate metric socket, and remove it by hand to drain the gear oil. If the differential is a cover-service unit with no drain plug (as is typical on this vehicle), instead loosen the cover bolts, break the cover seal, and allow the gear oil to drain into the pan before fully removing the cover. Inspect any magnetic drain plug or the magnet on the cover for metal particles or debris.
4. 4

   Inspect drained fluid and drain plug
   Allow the differential to drain completely (approximately 10-15 minutes). While draining, inspect the condition of the drained gear oil. Normal oil will be translucent amber to brown with a gear oil odor. Look for excessive metal particles, water contamination (milky appearance), or burnt smell indicating potential internal damage. Inspect the magnetic drain plug for normal fine metallic dust (acceptable) versus large metal shavings or chunks (indicates potential differential damage requiring further inspection).
   ℹ️Some fine metallic dust on the magnetic drain plug is normal. Larger metal chips, chunks, or excessive accumulation may indicate bearing wear or gear damage and should be investigated further.
5. 5

   Clean and reinstall drain plug
   Clean the magnetic drain plug thoroughly with shop rags, removing all metal particles and old fluid. Clean the drain plug sealing surface on the differential housing. Install a new drain plug gasket/washer onto the drain plug. Thread the drain plug into the differential housing by hand to avoid cross-threading, then tighten to the specified torque value using a torque wrench.
6. 6

   Refill differential with fresh gear oil
   Using a fluid pump or squeeze bottle with extension tube, insert the nozzle into the fill plug hole. Slowly pump GL-5 rated 75W-90 synthetic gear oil into the differential until oil begins to seep out of the fill hole. If the gear oil is not already formulated for limited-slip differentials, add the manufacturer-specified quantity of limited-slip friction modifier additive. The differential is full when fluid reaches the bottom of the fill plug threads. Allow a few moments for the fluid to settle and top off if necessary. Fill until fluid reaches the bottom of the fill plug threads; total capacity is approximately 2.5 quarts, but verify the exact capacity against the factory service manual for this specific differential.
7. 7

   Reinstall fill plug
   Clean the fill plug sealing surface on the differential housing. Install a new fill plug gasket/washer onto the fill plug. Thread the fill plug into the differential housing by hand to avoid cross-threading, then tighten to the specified torque value using a torque wrench. Wipe away any excess gear oil from the differential housing exterior.
8. 8

   Lower vehicle and verify service
   Verify both drain and fill plugs are securely tightened. Remove jack stands and carefully lower the vehicle to the ground using the floor jack. Remove wheel chocks. Start the engine and allow it to idle for 30 seconds. Start the engine briefly to confirm no leaks, then perform a short test drive at low speed to circulate the gear oil through the differential before final leak inspection. Turn off the engine.

Reassembly

1. Differential service is complete once fill plug is reinstalled and vehicle is lowered.

Verification

• After lowering the vehicle, inspect the area around both the drain plug and fill plug for any signs of gear oil leakage.
• After the test drive, re-inspect both plugs for leaks. No oil should be seeping from either plug.
• Take a brief test drive (5-10 minutes) at varying speeds, including turns and acceleration. Listen for any unusual whining, grinding, or clunking noises from the rear differential that were not present before service.
• Proper service is indicated by no leaks from drain or fill plugs, smooth differential operation without unusual noise, and normal clutch pack engagement in turns (for limited-slip differential).

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