82 300SD Diff and Rear Axles R&R - PeachParts Mercedes-Benz Forum

skaa · #1 07-29-2002, 02:32 AM

I've researched this forum, and PM'd a few posters, but no luck so far with my problem. My 300SD, (299k miles), has been " clunking" more and more over the past 50k miles, and given the end play in my passenger side rear wheel, I've decided to replace both half axles, as well as the differential. I just replaced the driveshaft and flex-discs last month, and no improvement. I have the CD and the Haynes manual, and both mention a special tool needed to press the half-shafts out of the hubs to remove them, as well as, (I think), to re-insert them. As best I can make out, the tool allows the half -shaft to be pulled into the hub splines the final few inches.
My questions: Must I use that tool, or can they just be tapped out, and in?
Anything special I need to know about the R&R of the differential?

Much thanks in advance for any insights.
SteveKaa
____________________________________________________________
1982 300SD 299k
1984 300D 165k (Ex-wife has it now)

burnan · #2 07-30-2002, 09:12 PM

Hi Steve,
I just replaced one of the axles on my '80 300D. I didn't use a special tool, just a dowel and a hammer to drive the axle out of the hub. I'm not positive on the 300SD though. It would be my guess that the clunking is just the CV joints. The boots on the passenger side of my car dried out and broke open. Of course all the oil flew out. The joints were so loud it was embarassing. It was so bad that the car shook while driving at highway speed. Any special reason why you want to replace the differential?

Andy B

skaa · #3 07-31-2002, 02:42 PM

Hi Andy,
The reason I think it's the differential comes from a series of posts between 240Joe and 84300DT and others last May on the subject of differential play/backlash. I tested my car on a lift and had almost 4" of extra play at the rear passenger wheel. When I hold the driveshaft still, I get the wheel travel, and it's obvious it's in the differential and not the axle. The boots are cracking and leaking a small amount at the wheel and the diff.
My original question was posted because everyone seems to have done the rear axles on 300D, 300DT, 300CD, etc, 123 bodies, but I can't find any reference to a 300SD w/126 body. The manuals indicate a slightly different procedure for 300SD, because of the extra hardware on the 300SD wheel, torsion bar, etc. The hardware is all original, meaning I've gotten 20 years and 300k miles from them. Time for the original team to sit on the bench and let some new talent take over!
Thanks for your reply, and I hope someone who has done a 300SD w/126 body will join in on this discussion.

SteveKaa

skaa · #4 08-24-2002, 01:12 AM

Just to finish up this thread. Another website said I may or may not need the special tool, depending on the conditions of the receiving splines. They turned out to be in excellent shape, so no special tool needed. But, I did have to lower the shocks to get enough clearance (barely 1/2") to take the half-axles out of the hub splines. The new rubber rear mount for the differential had trouble lining up, so I had to lower the springs all the way, thus I had to re-compress them to re-install them and the shocks. An unexpected job, but not difficult.
Total R&R time for half-axles and differential, 6.5 hours. No more differential whining, no more wheel play, and the rear end never rode better! However, it did not remove the "thunking" at each gear shift and downshift, but thanks to a series of recent posts by AdamB, I realize that is most likely a vacuum problem, so I'll be overhauling my vacuum pump gaskets shortly, and tracking down any loose or open vacuum hoses/connections. This forum is a really positive resource for the DIY crowd!

SteveKaa

1982 300SD 300k

Ken300D · #5 08-24-2002, 10:11 AM

What was your source for a differential - and was it new or used?

And if you don't mind saying, how much money are we talking about on just the differential?

I have new axle shafts on my 300D, and the flex disks look good. Still have considerable play and clunks in the differential along with whine. Not sure its worth the effort to replace, but I wanted to ask about the cost.

There's no shimming or adjustment possible on the differential is there?

Ken300D

Palangi · #6 08-24-2002, 10:12 AM

I put a new (used) differential in mine a couple months back. This car had always shifted very rough, especially 1-2, had clunks in the driveline, etc. The car developed a roaring noise, like a bad wheel bearing. I took it to my mechanic, who diagnosed it as a bad rear wheel bearing, which he was not equipped to fix. Took it to an MB shop, who diagnosed it as a bad pinion shaft bearing. (Had sparkely metal chips in the oil). Installed a differential (complete rear axle, actually) from a wrecking yard.

The clunking is gone, the rough shifting is gone, and, to my amazement, so is the 20% error in speedometer and odometer readings! Turns out, this car had the wrong differential in it when I got it!! The rough 1-2 shift was because it was winding up to too high of RPM's before shifting. An extra bonus is the true fuel mileage is up from the low to mid 20's to the mid to high 20's. Also, I now have some good spare half-shafts.

Bottom line is, I suspect the true mileage may be higher than shown. This was a one owner, little old lady car, which was showing 97k when I got it, and the stamps in the maintenance book for it's early years seemed to support that. I always was a bit suspicious about the speedometer error, but then, none of the 123 speedometers seem to read perfectly accurately. I never would have imagined that the differential would have been changed in 97k. The only other thing i have found to be suspicious was the non-MB water pump, but I imagined that to be possible in 97k.

Like they say, these cars wear so well, it is really hard to tell for sure if they have been rolled back.

psfred · #7 08-24-2002, 11:16 AM

I know of at least one other case were the wrong diff was installed at the factory (long story about the local dealer -- they broke a tooth off the ring gear while messing about with the car and refused to fix it, won the case, too!).

Probably was in there all along.

Peter

skaa · #8 08-25-2002, 02:03 AM

Ken300D,
I got my 1982 300SD 3.07 rear differential from a local wrecking yard, Trolley Auto Parts, here in San Diego, for $200. It was used, and came with a 101 day warranty. I looked on the Web at another site in Sacramento, CA, and they wanted a total of $275 to ship a used one to me with a 6 month warranty. (Silver Star Recycling) Another local yard wanted $300 for one. The one I got was in excellent shape, and was clean, tight, and crisp.
I installed my rebuilt half-axles into the differential on a work table and I looked at and photographed all the internals I possibly could. (All I've ever seen were drawings and diagrams of the inside of a differential). Everything lined up crisply, so I then lifted the whole mess into place with a friend securing the diff bolts and inserting the half-axles into the wheel hub splines. As to the shimming process, I've seen reference to it on the MB disc, but it looked like it took a few more bits of knowledge, parts, and courage than I had available.
Looking back on it, I'm happy I replaced the diff and the half-axles at the same time, as it removed a major source of noise and worry about the rear end mechanics of my car. Next month I'm going to replace the rear wheel bearings as well. My car has 300k miles on it, and it is my daily driver, so I'm really just getting it ready for the next 300k! Hope this helps you...

SteveKaa

psfred · #9 08-25-2002, 11:04 AM

I've been told my an MB factory trained tech that MB rear ends can indeed be rebuilt, but it is such a PITA that almost no one does. Requires a number of special jigs to measure things properly, not at all like a Dana.

Ditto for the manual tannys -- Hans says he could rebuild an NSU three speed in less than an hour with a Cresent wrench and a bit screwdriver and mallet, but an MB fourspeed was beyond him -- the last time he saw one done, it took the factory guy a whole day just to replace the main shaft bearings. Everything is shimmed, and it again requires special jigs to do the correct measuring.

Peter