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Pelican Technical Article:

Changing the Differential Fluid

Mike Holloway

Tools:

14mm Allen socket, universal joint, 12? extension for the socket wrench, lube fluid oil pump, floor jack, jack stands, wheel chocks, safety glasses, torque wrench

Applicable Models:

Mercedes-Benz R107 (1972-89)

Parts Required:

Differential Oil SAE 75W-85 Pelican Part #001-989-33-12-M22, Lube Fluid Oil Pump Pelican Part #SL4344

Hot Tip:

Use penetrating spray around the fill port and drain port

Performance Gain:

Longer differential life

Complementary Modification:

Change the engine oil

A differential is a gearbox similar to the transmission except its main function is to redirect the movement of the driveshaft. Like all gearboxes, it generates heat and friction while in operation. Just like in an engine, regular oil changes help to keep the bearings and gears inside well lubricated and clean but mostly the oil protects against wear. Over time, the differential wears just like any other part. However, it has no internal filter to capture small particles of metal as the gears wear. Usually, differential oil is good for up to 80,000 miles without changing, however it is commonly overlooked. Failure to change the fluid at regular intervals can eventually cause the bearings in the differential to fail.

Many folks think that it is best to run the car for at least 20 minutes to get the oil circulated and all the contaminates suspended. Actually a better reason to drive would be to warm the oil so that it would actually flow better.

You may have to jack up your car. Some people told me it can be done without having to while others say it makes it easier to work. If you decide that you would like some room, you will have to raise both ends of the vehicle, as the fluid level needs to be set with the vehicle level. Please see our article on safely jacking up and supporting your car. If your differential is dirty clean around the plugs so no dirt or debris will get into it while you are working.

Before you do any work on your car it is important that you wear safety glasses and wear work gloves. If you have to jack up your car, make sure to use jack stands and chock your wheels as well as applying the parking brake. Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. Never work on your vehicle if you feel the task is beyond your ability. Always disconnect the battery before working on your car.

There are two plugs on the differential.
Figure 1

There are two plugs on the differential. The fill plug is on the left side and higher than the drain plug. The drain plug is on the lower right side. As with any fluid change always make sure you can remove the fill plug BEFORE you drain the fluid. If you drain the fluid and then cannot get the fill plug out you will have no way to drive to a store and get anything to help you remove the fill plug.

Use a 14mm Allen, a universal joint and an extension so you can get around the exhaust and loosen the fill plug.
Figure 2

Use a 14mm Allen, a universal joint and an extension so you can get around the exhaust and loosen the fill plug. You won't have to remove it but make sure it will be able to be removed. It's important to do this before you attempt to remove the drain plug. 

Place a collection pan or bucket under the differential and remove the 14mm Allen plug with the same wrench configuration you used earlier.
Figure 3

Place a collection pan or bucket under the differential and remove the 14mm Allen plug with the same wrench configuration you used earlier.

Let the differential drain completely.
Figure 4

Let the differential drain completely. Then reinstall the drain plug.

Check the drain plug for any dirt, debris or metal shavings (red arrow).
Figure 5

Check the drain plug for any dirt, debris or metal shavings (red arrow). Small metal shavings are normal but any large bits or pieces are a sign of serious trouble.

Due to the location of the fill hole you will need to use a fluid pump to get the fluid into the differential.
Figure 6

Due to the location of the fill hole you will need to use a fluid pump to get the fluid into the differential.

Fill the differential with 75W-85 Differential fluid until the fluid starts draining out of the fill hole.
Figure 7

Fill the differential with 75W-85 Differential fluid until the fluid starts draining out of the fill hole. Reinsert the fill plug and tighten. 



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Page last updated: Mon 12/5/2016 02:53:41 AM