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Rear Differential Fluid Change
 
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Pelican Technical Article:

Rear Differential Fluid Change

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$25

Talent:

*

Tools:

14mm Allen head socket with breaker bar

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Differential drain and fill plug, differential oil

Hot Tip:

Working on a slightly warm differential

Performance Gain:

Extend life of differential

Complementary Modification:

Inspect and replace cracked axle boots if necessary
Your engine produces energy, which is measured in torque. The engine is the power-producing item in your car's powertrain. The engine's energy is transferred from the torque converter to your automatic transmission. Depending upon whether you're going from rest or at highway speed, the automatic transmission has your car in the correct gear. This energy or torque is transferred back to the differential and rear axles by the propeller shaft, also known as driveshaft. The differential has ring and pinion gears, which drops the engine rpm as the speed of the vehicle increases. The rear differential uses gearing to transfer the energy from the driveshaft to usable energy for the left and right axle shafts and hence to the car's rear wheels and tires. 

Gear oil lubricates these gears while the car is being driven. The ring gear runs through a bath of gear oil to lubricate it as it spins and meshes with the pinion gear. Over time this fluid can break down and lose lubrication qualities. While gear oil often lasts a long time, it is a relatively inexpensive repair to replace your rear differential oil. Replacing your differential oil at the factory specified maintenance intervals helps extend the life of your rear differential. In this tech article we will go over the steps to replace your differential fluid. 

Drive your vehicle for about 3 minutes to warm the fluid. This makes draining the differential fluid easier. 

Refer to our Jacking Up Your Vehicle article to lift your car and safely put it on jack stands. Also make sure to wear safety googles anytime you're working under vehicle.

This picture illustrates underneath the rear of the car looking at the rear differential.
Figure 1

This picture illustrates underneath the rear of the car looking at the rear differential. Locate the differential fill plug on the right side of the differential. Remove the fill plug with the 14mm Allen head socket and socket wrench. If the differential is full a small amount of oil will drip out of the fill hole. If not you can put your finger in the hole and see what the oil level actually is. Be careful, the thread machined into the differential case can be very sharp.

This picture illustrates underneath the rear of the car looking at the rear differential.
Figure 2

This picture illustrates underneath the rear of the car looking at the rear differential. Locate the differential drain plug (green arrow).

Remove the 14mm drain plug.
Figure 3

Remove the 14mm drain plug.

The view provided now is looking back at the drain hole.
Figure 4

The view provided now is looking back at the drain hole. Allow the thick gear oil to drain for several minutes. Once completely drained, reinstall the drain plug.

You can use a hose to exchange the new differential oil from the container to the fill hole.
Figure 5

You can use a hose to exchange the new differential oil from the container to the fill hole. Squeeze the bottle and the gear oil will be forced up the hose into the differential.

Fill the differential until oil starts to drip out of the fill plug.
Figure 6

Fill the differential until oil starts to drip out of the fill plug. Now the differential is full.

Fit the oil fill plug and tighten it down.
Figure 7

Fit the oil fill plug and tighten it down.

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Page last updated: Sun 4/23/2017 02:28:51 AM