DIY: W124 Differential Replacement

[skiier3_9]

I did this project at the same time as I removed one wheel carrier (for wheel bearing replacement). This was a more difficult project - especially without a lift.

Special Tools Needed
- 10mm XZN Sockets (eBay ~$40)
- 46mm open end wrench or large crescent/pipe wrench
- 8, 12, 14mm hex keys (eBay ~$30)

I. Jack both rear wheels up, put the car on jack stands, and remove the wheels.

II. Remove the rubber exhaust supports at the rear muffler, as well as the next exhaust support (2x13mm bolts). See pic #1 and 2. I used a jack to lift the exhaust and a pliers/screwdriver to grab and pry the rubber mounts around the muffler. Don't forget to support the exhaust once its down.
**Note - on V8 models you've got a bit more work - according to the manual you need to remove the complete exhaust system.

IIB (with ABS only - no ASR) - remove the ABS speed sensor (according to the manual). It also says drain the oil - we skipped this, but it would make it a bit lighter.

III. Remove the center exhaust shield (3x 8mm bolts). With the exhaust lowered you'll be able to twist this around the exhaust and out of the way. I also removed the front exhaust support where the front of the heat shield screwed into to give myself a couple extra inches of space. I don't know if this helped or not - there were 4x 13mm bolts holding this on.

IV. With the exhaust lowered and the heat shield removed you can remove the two 13mm bolts holding the center drive shaft support bearing in place. See Pic #3. As a precaution I painted a stripe on my drive shaft with nail polish in the event that the shaft became separated. This is where you would be well advised to get a 46mm open end wrench. With the car in park you can use the transmission to hold the front portion of the drive shaft to loosen the rear bolt. It isn't on very tight, but its a big pain because there isn't very much room. Others here have said a 15" crescent wrench fits - I tried an 18" without any luck and used a pipe wrench.

V. Unbolt the 3 19mm bolts that hold the flex disc to the differential. I removed all of the bolts so that I could remove/inspect the flex disc. I didn't need to replace mine (although originally I planned to). Pic #4 shows the drive shaft bolts removed.

VI. Once you've loosened the flex disc you need to slide the drive shaft off the differential's centering pointy thing. I used an 18" pry bar - the manual suggests a "suitable drift" whatever that is You can rest the drive shaft on the seatbelt bracket attachment (see the pic - its at the top).

VII. Now remove the axle bolts (6 per side) these require the 10mm XZN (or triple square) drivers. I purchased a set of 4 on ebay for about $40 shipped - not great quality but they worked. These bolts were extremely dirty on my car - I sprayed engine degreaser at all of these then inserted/removed the XZN a few times to remove some of the grease that had built up. I wanted to ensure that I got a really good seat of the XZN. I also had to use a breaker bar on my 1/2" drive socket (actually a 32mm box end wrench) to loosen these bolts. They are secured with blue lock-tight; heat might help, but I didn't have a torch and made due. See pic #5 - once I loosened the bolt I used a long extension to remove it all the rest of the way.

You'll need to use the parking brake to prevent the axle from turning while you loosen the bolts. You also can only loosen one or two in any one position - because the axle boot prevents you from getting the XZN securely in the head with the bolt at the bottom and the frame is in the way along the top/rear.