Tools:
- 14 mm hex bit socket or 17 mm.
- Ratchet for 14 mm or 17 mm hex socket.
- Oil Drain Pan. I use the Lisle Black Pan.
- Ramps, Jack and Jack Stands
- Oil transfer pump or suction gun.
- Differential oil. I prefer Red Line 75w90 since Mike Miller (Roundel & Bimmer columnist) uses Red Line in his maintenance schedule. Buy two quarts.
- New fill and drain plugs. Part #33117525064
- Plug washers for fill and drain plugs. Part #07119963355
- Rags, gloves, respirator (differential fluid is foul smelling), degreaser or kitty litter to clean any spills. Wear old clothes that you can throw away, you do not want to stink up your house or washer with differential oil.
- Jack up E39 and place on jack stands. I drove up on RhinoRhamps and jacked up the rear.
- Make sure the car is level by using the same jack stands or ramps at all four points. If you do not the same jack stands or ramps, a torpedo level will help in getting the car level.
- I highly recommend jack pad adapters to avoid crushing side plastic jack points.
- I use a low profile jack like Arcan's to avoid damage to the bumpers and rocker panels
- Use wheel chocks to prevent car from sliding while jacking.
- Locate the fill and drain plugs on the rear differential. See picture below
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| The plugs are wet because I sprayed PB blaster on them |
- Remove the fill plug FIRST with the 14 mm hex bit and ratchet. You want to make sure the fill plug can be removed before the drain plug.
- My plugs were badly rusted as the previous owner did not maintain the differential. I sprayed PB Blaster and let it soak for an hour to help loosen the plugs. A breaker bar may also be needed.
- Remove the drain plug with the same 14 mm hex bit and drain fluid into a drain pan. Draining will take a while as differential fluid is thick.
Old and new plugs. - Place new washer on drain plug and install. Torque to 52 ft-lbs.
- Add differential oil through fill plug hole. Use a quart pump, transfer pump, or suction gun to transfer oil. I used about 1.5 quarts to fill my differential.
- Place new washer on fill plug and install. Torque to 52 ft-lbs.
- Check for leaks and lower car by removing jacks, ramps, wheel chocks.
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| Here are some of the tools I used for this job. |
That's it. Pretty simply job to do yourself and it is a lot cheaper than going to the dealership.
Notes:
- Mike Miller recommends performing this service every 30,000 miles to maintain the differentials.
- Some E39 drivers have said changing the differential fluid has stopped the humming or purring noise.
- Please be safe in lifting your E39, if you have never done it or don't feel comfortable, bring your car into the shop to have the service performed.
power steering fluid after '06 with their E9X models. The Pentosin fluid is not compatible with ATF! Do not mix the two. The required fluid is stamped on the top of the reservoir cap as shown below.
. If your reservoir requires Pentosin I would keep your old cap and put it on the new reservoir. 
