Differential Fluid Change - Front

Drain and refill the front differential with fresh gear oil to maintain proper lubrication and extend component life.

Warnings

Tools required

Parts

• Front differential drain plug seal/washer × 1 — Mercedes OEM copper or aluminum crush washer
• Front differential fill plug seal/washer × 1 — Mercedes OEM copper or aluminum crush washer

Fluids

• MB 235.0 or 75W-90 GL-5 synthetic gear oil — 2.6 qt

Preparation

1. Park vehicle on level ground and apply parking brake firmly
2. Place wheel chocks behind rear wheels
3. If differential has been driven recently, allow at least 30 minutes cooling time
4. Raise front of vehicle with floor jack and support securely on jack stands at frame rails
5. Verify vehicle is stable before working underneath
6. Remove both front wheels to improve access (optional but recommended)

Procedure

1. 1

   Locate differential plugs
   Position yourself under the front of the vehicle. Locate the front differential housing between the front wheels. Identify the fill plug on the passenger side of the differential housing (typically at the mid-height of the case) and the drain plug at the bottom rear of the differential case. Clean the area around both plugs with a wire brush and shop rag to prevent contamination when opened.
2. 2

   Break loose fill plug first
   Using a 14mm hex socket or wrench, break loose the fill plug first before draining. Turn counterclockwise approximately one full turn but do not remove completely. This ensures you can refill the differential after draining. If the fill plug is seized or stripped, do not proceed with draining until fill plug access is confirmed.
   ⚠Always loosen fill plug before drain plug. If fill plug is seized and you drain first, you cannot refill the differential.
3. 3

   Position drain pan and remove drain plug
   Position drain pan directly beneath the drain plug with at least 3 quart capacity. Using a 14mm hex socket or wrench, completely remove the drain plug by turning counterclockwise. Allow all gear oil to drain completely into the pan. This may take 5-10 minutes for complete drainage. Once draining slows to occasional drips, the differential is sufficiently drained.
4. 4

   Inspect and clean drain plug
   Inspect the drain plug threads for damage or excessive wear. Check the magnetic tip of the drain plug for metal debris. A light coating of fine metallic particles is normal; large chunks or excessive material may indicate internal wear requiring further inspection. Clean the drain plug threads with a wire brush and shop rag. Remove and discard the old crush washer from the drain plug.
5. 5

   Reinstall drain plug with new washer
   Install a new copper or aluminum crush washer onto the drain plug. Thread the drain plug into the differential case by hand to avoid cross-threading. Once hand-tight, use the 14mm hex socket and torque wrench to tighten to the MB-specified torque (verify against factory service data; do not assume 30 Nm). Wipe away any residual oil around the drain plug area.
6. 6

   Remove fill plug and prepare to refill
   Completely remove the fill plug that was previously loosened in step 2. Remove and discard the old crush washer from the fill plug. Set the fill plug and new washer aside in a clean location. Prepare your fluid pump or transfer bottle with gear oil meeting MB approval sheet 235.0 in the correct viscosity for this axle (verify spec/viscosity against MB service data).
7. 7

   Refill differential with gear oil
   Insert the nozzle of your fluid pump or transfer bottle into the fill hole. Slowly add MB 235.0 or 75W-90 GL-5 gear oil until it begins to drip or run out of the fill hole. The front differential capacity is approximately 1.5 quarts (fill to the bottom edge of the fill hole; verify exact capacity against MB service data). Fill until oil reaches the bottom edge of the fill hole and begins to overflow slightly. This indicates proper fill level. Allow a few moments for oil to settle and top off if necessary.
   ℹ️Proper fill level is reached when oil just begins to drip from the fill hole with vehicle on level ground.
8. 8

   Install fill plug with new washer
   Install a new copper or aluminum crush washer onto the fill plug. Wipe any excess oil from the fill hole area. Thread the fill plug into the differential case by hand until hand-tight. Use the 14mm hex socket and torque wrench to tighten to the MB-specified torque (verify against factory service data; do not assume 30 Nm). Wipe the area clean of any spilled gear oil.
9. 9

   Inspect for leaks and reinstall wheels
   Inspect both the drain plug and fill plug areas for any signs of leakage. Wipe clean and observe for fresh oil seepage. If wheels were removed, reinstall them and hand-tighten lug nuts in a star pattern. Lower vehicle to the ground.
10. 10

    Final torque and cleanup
    With vehicle on the ground and full weight on wheels, torque the wheel lug bolts to the MB-specified value (verify against factory data) using a star pattern. Dispose of used gear oil properly at a recycling center or automotive shop. Store any remaining fresh gear oil in a sealed container for future use.
    Torque spec

    Wheel Lug Nuts140 Nm (103 lb-ft)

Reassembly

1. Ensure both drain and fill plugs are torqued to 30 Nm with new crush washers installed
2. Wheel lug nuts must be torqued in a star pattern to 150 Nm with vehicle on the ground
3. Dispose of used gear oil according to local regulations

Verification

• Start engine and allow to idle for 30 seconds, then shut off
• Inspect underneath vehicle at drain and fill plug locations for any fresh oil leakage
• Test drive vehicle for 5-10 minutes, making several turns in both directions
• Re-inspect drain and fill plugs for leakage after test drive
• Check that no unusual noises are present from front differential during operation

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