Differential Pinion Seal

Replace the differential pinion seal on the rear differential to repair fluid leaks from the pinion shaft area.

Warnings

Tools required

Parts

• Differential pinion seal × 1 — Use OEM specification
• Pinion nut (if not reusable) × 1 — Use OEM specification
• Differential fluid gasket/sealant × 1 — Use OEM specification
• Shop towels × 1 — Generic

Fluids

• Mercedes-Benz Diff Fluid 75W-85 — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake.
2. Raise vehicle on lift or with jack and support on jack stands at proper jacking points.
3. Allow differential to cool completely if recently driven.
4. Place drain pan under differential.
5. Clean area around pinion flange and driveshaft connection to prevent contamination.

Procedure

1. 1

   Mark driveshaft alignment
   Use marker or paint pen to mark the driveshaft flange position relative to the pinion flange. This ensures proper phasing during reassembly and prevents driveline vibration. Mark both the flange position and individual bolt holes.
2. 2

   Remove driveshaft from pinion flange
   Remove the driveshaft U-joint strap bolts or CV joint bolts connecting the driveshaft to the differential pinion flange. Support the driveshaft and carefully lower it away from the pinion flange. Secure the driveshaft out of the way with mechanics wire to prevent strain on the center support bearing.
   Torque spec

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

   CV Bolts82 Nm (61 lb-ft)
3. 3

   Measure pinion bearing preload
   Using an inch-pound torque wrench on the pinion nut, measure and record the rotational torque required to turn the pinion through several complete revolutions. This is the pinion bearing preload and must be matched or slightly exceeded on reassembly. Typical reading is 3-5 inch-pounds for used bearings.
4. 4

   Mark and remove pinion nut
   Mark the pinion flange position on the pinion shaft with a paint pen. Install the pinion flange holding tool to prevent rotation. Using an impact wrench or breaker bar, remove the pinion nut. Keep the nut if reusable per manufacturer specifications, otherwise discard and use new.
   ⚠The pinion nut is under high torque. Ensure holding tool is secure before attempting removal.
5. 5

   Remove pinion flange
   Remove the pinion flange from the pinion shaft. A puller may be required if the flange is tight on the splines. Note the flange orientation and any shims or washers present. Keep all components in order for reassembly.
6. 6

   Remove old pinion seal
   Using a seal puller or carefully with a small pry bar, remove the old pinion seal from the differential housing. Take care not to damage the seal bore surface in the housing. Clean the seal bore thoroughly with brake cleaner and inspect for scoring or damage.
   ⚠Do not damage the pinion shaft surface or seal bore during removal as this will cause the new seal to leak.
7. 7

   Install new pinion seal
   Lightly coat the outer diameter of the new pinion seal with differential fluid. Using the appropriate seal driver, carefully drive the new seal into the housing bore until it is fully seated and flush with the housing face. Ensure the seal goes in square and does not cock to one side. Coat the seal lip with clean differential fluid.
8. 8

   Reinstall pinion flange
   Clean the pinion shaft splines and flange. Reinstall any shims or washers in their original positions. Carefully slide the pinion flange onto the pinion shaft, aligning with the marks made during disassembly. Ensure the flange is fully seated on the shaft.
9. 9

   Install and torque pinion nut
   Install the pinion nut (new or original if reusable). Using the pinion flange holding tool, tighten the pinion nut gradually while checking pinion bearing preload with the inch-pound torque wrench. Tighten until the rotational torque equals or slightly exceeds (by 1-2 inch-pounds) the original preload measurement. Do not overtighten as this will damage bearings.
   ⚠️Critical procedure: Pinion bearing preload must be set correctly. Too loose causes noise and wear; too tight causes bearing failure. Tighten incrementally and check frequently.
10. 10

    Reconnect driveshaft
    Align the driveshaft flange to the pinion flange using the alignment marks made during disassembly. Install the U-joint strap bolts or CV joint bolts and torque in a cross pattern to specification.
    Torque spec

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

    CV Bolts82 Nm (61 lb-ft)
11. 11

    Check and refill differential fluid
    Check the differential fluid level through the fill plug. Add Mercedes-Benz Diff Fluid 75W-85 as needed until fluid reaches the bottom of the fill plug hole (fluid should just start to drip out). Install fill plug with new gasket if equipped and torque to specification.
    Torque spec

    Cover Screws15 Nm (11 lb-ft)

Reassembly

1. Verify all fasteners are torqued to specification.
2. Ensure no tools or rags are left in the work area.
3. Lower vehicle to ground.
4. Check for fluid leaks after test drive.

Verification

• Start engine and verify no differential fluid leaks from pinion seal area.
• Test drive vehicle and listen for abnormal differential noises that would indicate incorrect pinion preload.
• After test drive, recheck pinion seal area for any signs of leakage.
• Verify smooth operation with no driveline vibration, confirming proper driveshaft alignment.

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