Bleeding the diff fluid

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Thu, 03/09/2026 - 21:42
g4lon
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Location: London

300GE - 1995
I tested the fluid in the diff resevoir and it's really bad.  It needs changing for sure. Can i bleed the system from the actuators just the way the brakes are done or is there a specific way for me to replace the fluid?

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Fri, 04/09/2026 - 10:35
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Re: Bleeding the diff fluid

Found this:

There should be a Diff Drain plug on the side, which is magnetised to catch metal dust.

https://www.youtube.com/watch?v=W3hibS14ZOM 

And from this site:

  • Oil: Hypoid gear oil meeting MB 235.0 (or equivalent API GL-5). Typical viscosity is SAE 85W-90 or SAE 90 (use SAE 90 in hotter climates). Examples include Mobilube HD-A 85W-90. Do not use GL-4 oil intended for the transfer case.
  • Capacity: Front axle ~1.4 L; rear axle ~1.8 L. One source lists ~1.6 L for an axle—fill until it just overflows the fill hole with the vehicle level.
  • Interval: Commonly every 40,000 km / 800 hours or about every 3 years (follow your workshop manual). Change more often if you do heavy off-road use.

Procedure

  1. Park on level ground, chock the wheels, and support the vehicle safely on stands if you need extra clearance. Warm the oil slightly by a short drive for better draining, but work carefully with hot oil.
  2. Clean around both plugs. Remove the upper fill plug first - 14mm Hex spanner (this confirms it will come out and prevents a vacuum). Then remove the lower drain plug and let the oil drain completely. Inspect the old oil and magnetic drain plug for excessive metal—fine paste is normal; chunks or glitter can indicate wear.
  3. Clean the drain plug and hole. Reinstall the drain plug with a new washer or suitable sealant and tighten securely (typical range discussed for these older Mercedes diffs is roughly 50–80 Nm; do not overtighten).
  4. Pump new oil in through the fill hole until it just starts to overflow. Reinstall the fill plug the same way.
  5. Wipe everything clean and check for leaks after a short drive. Repeat for the other axle.

The same 14 mm hex size is used on both plugs of both axles. Front access can be tighter; a short hex bit plus wrench on the exposed flats sometimes helps.

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