Where or how do you change the differential fluid??
 

All this work I've been doing on my car and I have not done the differential fluid. How does one go about doing this? Where is it located for my W201?

All that's needed is a 17mm allen. Be sure to remove the fill plug before the drain plug.

John M, thanks, but where is the fill hole and drain plug located? I've never done this job before. Do I need a filter?

Once you look at the diff it is pretty obvious. Fill plug is on the passenger side of the diff IIRC. Drain plug is on the bottom :)

No filter. Be sure to use GEAR OIL, not ATF or anything else.

when changing differential oil loosen the filling nut first then the drain nut . Occasionally the top fill plug refuses to budge and can be troublesome if you have already drained the oil.

lsmalley, check your Owner's Manual for the type gear oil specified for the differential (normally 90W or 85W90). If your car has ASR you should buy differential fluid from your local MB dealer.

As mentioned remove the fill plug before draining the old fluid. Add new fluid until it's up to the fill plug hole. Either pump it into the differential, or you can remove the drain plug from the spare tire well and use clear tubing from the container through the drain plug hole into the differential. Whatever works best for you.

17mm allen? i would have said 14mm.

ok guys, I hate to say it, but I still don't know where it is. Can someone provide a picture or two? Not sure if I need to go under the car or in the trunk or what :-(

it's the large pumpkin shaped part between the two back wheels. UNDER the car. you will need a lift of some type. either a pit a floor jack to raise each side and jackstands to support the vehicle. drive up ramps will also work. be safe!

Yes, it is actually 14mm allen, not 17mm, sorry. I was thinking about the Volkswagen transmission drain plug which is 17mm.

The differential is between the two back wheels, attached to the drive shaft that runs up under the car to the transmission.

I recommend cleaning around the fill plug before you remove it. Sure dont want dirt getting into the gearcase!

Use a mirror to find the fill plug.

Oh, did anybody mention that you're supposed to remove the fill plug first?

Step 0: Consult your owners' manual for information on the type and quantity of fluid used in the differential. purchase in advance of the work and write the brand and type down someplace.

Step 1: Drive to the car wash and spend abput 3.00 on hot water and soap to clean off that big round thing in the middle of the rear axle. Wear dirty clothes when you do this at the car wash. A poiece of cardboard or rubber mat to lie on is handy, go at it from both sides.

Step 2: Drive home and let it dry.

Step 3. Assemble these as minimum tools
- hydraulic jack
- two hydraulic jack stands
- two spare rims
- 1 x 1/2" breaker bar with 24" handle
- 1 x 1/2" drive ratchet and short (2") extension
- 1 x 1/2" drive torque wrench
- 1 x allen wrench socket of the correct size
- 1 x oil pan to collect the used lubricant
- Antiseize compound (optional)


Step 4: Set parking brake and put vehicle in park, then use the hydraulic jack to lift up the vehicle and install the jacks under the jacking points per the owner's manual.

Step 5: Get clear of the vehicle and shake it to make sure it is firmly on the jack stands

Step 6: Place a tire rim under each wheel to allow for an emergency space just in case

Step 7: assemble the breaker bar+ Allen socket, lay the mat down, locate the top-mounted fill plug area. Install the Allen wrench firmly and deeply inside the plug, turn counter clockwise and attempt to break the plug free. If necessary, add a pipe to the breaker bar and slowly lever the bar until the plug is free moving.

Step 8: Replace the breaker bar with the ratchet+socket and remove the plug. Clean it thoroughly with gas, parts cleaner, etc until it is 100% clean. Set it aside.

Step 9: Locate the drain plug. Install the Allen socket plus breaker bar and break it free but do NOT remove yet.

Step 10: Place the drip pan under the drain plug area, use the ratchet and socket to remove the drain plug and let fluid drain into the pan. In the meantime clean the drain plug.

Step 11: Optionally, put a thin coat of anti-seize on the drain plug and the fill plug.

Step 12: Gently install the drain plug by hand AFTER all fluid has drained. Then use the Allen wrench to tighten it a little more AFTER you have started it by hand. Use the ratchet to tighten it firmly, then use the breaker bar to provide the final tightening torque.

Step 13: Slowly pour the correct measured amount of fluid into the diff by hand. Wait until it settles, do not pour so fast that you spill. Then install the fill plug as prescribed in step 12 but for this plug.

Step 14: Remove the drain pan and wipe the diff clean at the top and around the drain plug, so that it does not give you a false impression of a leak.

Step 15: Remove all tools from the area under the vehicle until there is nother there but the jack stands.

Step 16: Jack up the kehicle and remove both rims and then, both jack stands. Keep them far out of the way.

Step 17: Slowly lower the vehicle using the hydraulic lift and pull it away from the vehicle.

Step 18: Make certain all tools and equipment are accounted for and clear of the vehicle.

Step 19: Start the car and back it away from the work area. Slide a piece of cardboard under the diff to check for leaks.

Step 20: Conduct recovery-- clean and replace all tools and equipment. Check later for possible leaks and remember that you must safely secure the vehicle before going under it again.

:D

Now that is a detailed description of the procedure!

You can also use a generic fluid hand pump from a local auto store to pump the fluid out of a normal bottle through the fill plug. Saves you having to tear up the trunk.