SLK32 Differential Oil Change

Changing the Gear Oil in the SLK32 Differential

Equipment:

1. A 14mm Hex (Allen) wrench. I recommend a socketed bit and a 1/2-inch drive ratchet instead of the L-shaped key-type wrench because there's not much room to maneuver a key-type wrench. There's a good chance you don't have a size 14mm in your tool box (Craftsman doesn't even make one). It can be purchased from a tool store or online. A 1/2-inch drive socketed 14mm hex bit is $23 from Snap-On. I bought a complete set of socketed metric bits on Ebay for under $20.

2. Differential fluid. The differential holds just a little more than 1 quart, So you'll need to buy two quarts. The factory fill is non-synthetic 90W, according to another SLK32 AMG owner. I used Mobil 1 75W-90 full synthetic which costs about $7 per quart.

3. A fluid pump. Most auto parts stores offer hand pumps for differential fluid. They fit right on the bottle and cost only $3 or so.

4. Thread sealer. Many are available. I used Permatex High Temperature Automotive Grade Thread Sealeant (Part number 59214). It costs about $4 at my local auto parts store.

5. Oil drain pan. A pan with a profile of 4 inches or less is best.

Safety tips:

1. These instructions do not require you to use a jack, jack stands, or ramps. The car should be level for this job and I don't recommend jack stands or ramps because of the danger to yourself and your car when working under a car with all 4 corners raised. It might be a tight fit, but you should be able to do it with the car on the ground.

2. Your car's exhaust should be completely cool. While there may be some benefit for changing the differential oil when it's hot, you will be working right next to the exhaust pipes and working in a cramped space puts you at an even higher risk for burns if the exhaust is hot.

3. Wear work gloves at all times to protect your hands from cuts and scrapes.

4. Wear eye protection at all times to prevent dirt and oil from getting into your eyes.

Procedure:

1. Position the drain pan under the differential housing.

2. Remove the fill plug. The fill plug is located near the front of the differential housing on the driver's side. Use a rag to wipe off any dirt or grease around the fill plug, then use the 14mm hex wrench to unscrew the fill plug. A small amount of fluid may drip out when you remove the plug so make sure the pan is under the differential housing. It's important that you remove the fill plug now because if you remove the drain plug first and then find out you can't remove the fill plug for some reason, you'll have no way to refill the differential.

3. Remove the drain plug. The drain plug is located near the bottom rear of the differential housing on the passenger's side . Use a rag to wipe off any dirt or grease around the fill plug, then use the 14mm hex wrench to unscrew the drain plug. The fluid may shoot out of the differential a few inches when you remove the plug, so position the drain pan appropriately. Wait for all of the fluid to drain.

4. Install the drain plug. Clean the drain plug thoroughly and apply some thread sealer on the plug threads according to the directions on the package. Use the 14mm hex wrench to screw the plug back into place. Wipe off any fluid from the differential housing.

5. Fill the differential. Insert the pump into the bottle of new fluid, insert the pump hose into the fill plug hole and pump the new fluid into the differential. There probably won't be enough clearance to stand the bottle upright with the pump in it, however, the pump should seal tightly to the bottle and you can lay the bottle down and pump if necessary. When the first bottle is empy, switch the pump to the other bottle and continue pumping until fluid begins to run out of the hole. Make sure that the pump outlet hose is correctly inserted into the fill plug hole, otherwise fluid may run out of the hole before the differential is full.

6. Install the fill plug. Clean the fill plug thoroughly and apply some thread sealer on the plug threads according to the directions on the package. Use the 14mm hex wrench to screw the plug back into place. Wipe off any fluid from the differential housing.

7. You're done. Put away all of your tools, clean yourself up, and return the old fluid to an oil recycling facility.