Originally Posted by Jeremy5848

Here is what I learned from replacing the axles of my 1985 Mercedes 300D Turbo (the boots were torn). Many of these learnings came from reading this forum. Implied thanks to all who unselfishly donated their hard-earned knowledge. "How-to-do-it" has been posted by others previously; this is a "rest of the story" story. Caveat: this is how I did the job. Your mileage may be different.

This is definitely a job that most of us can do. It doesn't take any special tools or knowledge beyond common sense and can save you a pile of money, especially if your mechanic is expensive and wants to use new parts from Mercedes.

1. You don't need a lot of tools and supplies
Pair of jack stands and wheel chocks
Metric 1/2 inch drive socket set
Torque wrench
Pry bar (18 inch minimum) for removing old seals
Snap-ring pliers or other hooked device for axle c-ring
14mm Allen wench with 24" extension (pipe) for the differential plugs
Propane torch in case the differential plugs are really tight
Drain pan
Work lights
Rags (lots)
Teflon tape for drain and fill plugs
90 weight gear oil
Loc-tite or similar thread-sealing compound (the blue kind)
Silicone sealant for differential cover

2. Preparation is important. If possible, degrease and pressure-wash the underside of the car. If your axle boots are leaking like mine were, the underside of the car will be coated with oil. A clean, flat place to do the work is nice. You'll be spending a lot of time on your back under the car. Be sure to chock the front wheels securely; they are the only things keeping the car from rolling (especially important if your site has an incline). Try to have everything you need beforehand and don't start without the big Allen wrench like I did (and then discover that most stores carry up to 10mm only).

3. I used an old cardboard box as a bolt holder, making simple drawings on the box and punching holes for each bolt. That way, each bolt went back into the same hole.

4. The factory recommends new bolts for the brake calipers and for attaching the "rubber bearing" to the floor of the car. However, this is only because the bolts have locking compound on them. All you have to do is to get some Loc-tite or a similar fluid (the blue kind) and you can clean and reuse the old bolts. The 8mm bolt that holds the axle to the wheel hub uses a cupped washer that the factory calls a "clamping disc." This washer distorts when torqued and is supposed to be used once only. Since I did not have new washers, I turned the old ones over. I do plan to replace these washers, since they are easy to get at.

5. Removal of the brake calipers is necessary only if you have trouble getting the axles out and have to lower the semi-trailing arm (by unbolting the shock absorber) to get more clearance. (I didn't have to do that.) However, it is handy to have the calipers out of the way so you can see better. The books recommend hanging the caliper with a piece of wire (saves the brake hose) and I also found that I could put the caliper up on top of the wheel hub where it is out of the way.

6. The drain and fill plugs in the differential may be tight. Make sure you can get the fill plug out before removing the drain plug. The fill plug is steel, screwed into the aluminum cover of the differential, and is especially prone to sticking. I ended up using a torch to warm the cover before the plug would break free, even with a two-foot piece of 1/2 inch steel pipe as an extension for the 14mm Allen wrench. I put Teflon tape on the plugs before I put them back; maybe it will help get them out next time.

7. When you pull the c-ring off of the inner end of the axle (inside the differential), it will probably go flying. Covering the differential with a shop rag will keep the ring from ending up in the next ZIP code. When I put the c-ring into the new axle, I used a pair of needle-nose pliers to get it started into the groove and then drove it home with a pin punch and a small hammer. This is a personal choice; use what works for you.

8. You don't have to replace the seals in the side of the differential (each axle goes through one) but it's a good idea. The left one in my differential showed signs that it was starting to leak. They were only six or seven dollars each. The FSM and Haynes both have this cute picture of the old seal being levered out with a long screwdriver. This is a joke. The seal is made of much sterner stuff and laughs at mere screwdrivers. I used an 18 inch wrecking bar and both feet.

9. Installing the new seals is not difficult. Lacking the factory tool (of course), I made one from a short piece of 3-inch ABS plastic pipe (the black stuff used for drains). If you sand or file the inside diameter a little, it will fit perfectly over the rubber lip on the seal. I put a cap on the other end of the pipe and gently hammered on it to drive the seal into its space in the differential. Putting a little oil on the outside of the seal helps it go in smoothly. The ABS pipe is slightly larger than the seal and stops when it hits the side of the differential. This turns out to be exactly what the factory tool does -- the seal is now properly seated.

10. There's a lot on this forum about replacement axles. Replacing the torn boots is possible, although special tools are required for the factory boots. An after-market "Flexx" boot is available although the special air-operated "Flexx-gun" is $250 unless you can find one on eBay or know a shop that will do the job for you. The Flexx boots are made from thinner rubber than the factory boots and will not last as long (ten years instead of twenty?). This is probably the least expensive way to go if you're short on cash. Since my axles had over 200,000 miles on them (1500 with torn boots), I decided to replace them. Rebuilt axles are available from many sources with prices under $100 but posters to this forum have reported mixed results. The least expensive new axle I found was $400 (each). In the end, I chose the rebuilt axle sold by CVJ of Denver for $142 each plus a $50 refundable core charge and shipping (40 pounds total). They have most axles in stock and can build one for you in a day or two if yours isn't on the shelf. I called them on a Tuesday and had the axles the following Monday.

11. The shim or spacer on the differential end of the axle must not be forgotten. When I removed the old axles, one spacer came out on the axle and the other stuck in the differential. The spacers are sized for the differential and each must go back into the same side. If the axle builder has done his job correctly, the axle will go into the differential, leaving just enough room for the c-ring to slide into its groove.

12. Remember to lube the splines and the new seal in the differential to help the axle go in smoothly and not damage the new seal. I had trouble getting the left axle to slide into the wheel hub, as the splines were very tight. I ended up buying some long 8mm bolts and used them to slowly draw the axle into the hub. Heating the hub with a heat gun, being careful not to damage the seal, might also have helped but that was a "next step" that I didn't need to take.

13. Once everything was back together, I refilled the differential. I used an oil pump container that I bought many years ago for filling BMW motorcycle transmissions. All I had to do is pump until the differential started to overflow, then removed the hose and screwed in the plug.

14. Before I took the car off of the jack stands, I started the engine and put the transmission in "Drive" for a few minutes, to make sure there were no bad noises or leaks.

15. After a week or so, I'll check all of the bolts to be sure they are still tight.