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BMW E39 Rear Differential Fluid Replacing
 
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Pelican Technical Article:

BMW E39 Rear Differential Fluid Replacing

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$35

Talent:

**

Tools:

14mm Allen key or socket with ratchet, jack and jack stands

Applicable Models:

BMW 525i Sedan/Wagon (2001-03)
BMW 528i Sedan/Wagon (1997-00)
BMW 530i Sedan (2001-03)
BMW 540i Sedan/Wagon (1997-03)

Parts Required:

Drain screw, fill plug screw, washers

Hot Tip:

If you have a limited slip differential then you will need an additive for the gear oil

Performance Gain:

Extend life of differential

Complementary Modification:

Replace axle flange seals

You engine provides the torque, and your rear differential takes the torque of the engine and distributes it to your two drive wheels. In the case of the E39 chassis that means the rear wheels. Hundreds of horsepower travels through your differential as you drive. It needs to be well lubricated if it is to last under these harsh conditions. As the pinion gear engages with the ring gear the two sets of teeth meet. This metal to metal contact is reduced by the gear oil in your differential. After many miles the gear oil breaks down and gets thinner from the mechanical action of gears meshing. Replacing the fluid is necessary to get back the necessary lubrication to protect the gears as they mesh.

When selecting gear oil grades take into account the climate the car will spend most of the time in and the type of driving you are going to be doing. Use an 80W-90 weight if you are in cold climates most of the year. Use 90W-145 weight if you are in hot climates or using the car as a part time race car. If you have a limited slip differential you need to add a hypoid additive (friction modifier) for the clutch packs in the differential. It is usually very easy to determine if you have a limited slip differential. Jack up both rear wheels and spin one tire. If the opposite tire spins in the same direction you have a limited slip differential. If the opposite tire spins in the opposite direction then you have a conventional differential.

To drain and refill your differential fluid you need to raise and support the rear axle of your vehicle. It is best to raise both axles to help achieve the proper fluid level when filling the differential. See our tech article on jacking up and supporting your vehicle.

This photo illustrates under the rear of the car on the right side looking at the rear differential.
Figure 1

This photo illustrates under the rear of the car on the right side looking at the rear differential. Use a 14mm Allen head socket or key to remove the differential drain plug. This plug will be tight and corrosion will make it harder to take off. It will require some strength or leverage to get off. There is a large washer around the drain plug. Be sure not to lose it or replace it with a new one.

Place a drain pan under the drain plug and thread the drain plug all the way out.
Figure 2

Place a drain pan under the drain plug and thread the drain plug all the way out. This gear oil will take some time to drain because it is thick,

We are now looking at the back of the differential case under the rear of the car.
Figure 3

We are now looking at the back of the differential case under the rear of the car. On the back of the pan is the fill plug (green arrow). Use a 14mm Allen key or socket and ratchet to loosen and remove the fill plug. The fill plug will also have a large washer on it so be careful not to lose it or replace it,

Install the drain plug and torque it down to specifications.
Figure 4

Install the drain plug and torque it down to specifications.

Add your gear oil through the fill plug opening.
Figure 5

Add your gear oil through the fill plug opening. In our case the rear sway bar was removed and that made it easier but you can use a syphon pump to draw the gear oil out of the container and into the differential. Or you can remove the swaybar bushings to get better access to the fill plug. See our tech article on rear swaybar links and bushings removal.

You are going to fill the rear differential through the fill plug.
Figure 6

You are going to fill the rear differential through the fill plug. Add fluid until you see fluid drip out of the lower edge of the fill plug hole (green arrow).

Install the fill plug and tighten it down to specifications,
Figure 7

Install the fill plug and tighten it down to specifications,

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Page last updated: Fri 12/2/2016 02:05:47 AM