My car has a clunk in the driveline, especially when coming to a stop, most noticeable during cold weather. Dealer diagnosis is worn differential, probably spider gear, which is what I had suspected anyway. Dealer's price for installing a factory rebuilt differential is about $1800. The 123 Chassis Manual shows rebuilding the differential and adjusting backlash with compensating washers. Obviously a big job with considerable skilled labor involved. Dealer does not want to rebuild it in-house because the final cost will come out about the same only without the warranty of a factory rebuilt unit. A used unit in unknown condition from Adsit is about $750 delivered, with no real way for a shade tree mechanic (me) to install it, so that does not seem like a good way to go. I would like to have some advice from the voice(s) of experience on how to proceed with this. The car is in good condition otherwise. Perfect engine, good transmission, good interior, good body with no rust, only other thing it really needs is some front end work which I have been putting off. All that being said, in real life, the cost of this work if done by the dealer will equal about 60% of the value of the car.

I had the same type issue arise when I when I broke something in my Acura's transmission. My mechanic explained it to me this way. A factory refurbished unit is rebuilt by experts who put the unit's back to new unit specs. You can't rebuild it any better than this. Beside that, with the warranty, if something happens, they just swap it out. No matter your shops experience in rebuilding these units, I can guarantee you that they are not setup to put the unit back to factory specs. With used, there is no way of knowing what you are going to get.

A good used diff from Mercedes bone-yard is the best way to go. I've bought at least 20 & never had any problems with used parts. Never paid more than $250 for that version!

Try calling Atlanta-Stuttgart Auto Parts. They gave me a very competitive quote on a rear trailing arm on my 300SD.

My car clunks to some degree, much like yours. The source is worn spider gear bores/shaft. I think the play is somewhere between 1/32" and 1/64". I quietened the noise about 50% by switching to 85W140 oil. It's going to have to run this way until it blows up. Way too expensive to fix.

Gary

Your problem will be even more expensive if when you get that new unit in, it still klunks on stopping.

There is virtually no amount of backlash that will be felt if the transmission is properly downshifting. If your main problem is as the car goes to first gear at almost no speed then I think the problem is in the vacuum control of your tranny.

Stevebfl, you are absolutely correct that the clunk happens when the transmission downshifts while coming to a stop. Sometimes it is barely perceptable, other times it is very pronounced. I have no doubt that there is a lot of backlash in the differential, but, as you indicate, it shouldn't be noticable as long as the engine is always pulling. The car seems free of vacuum leaks, just judging by the prompt engine shutdown, and the fact that the central locking holds for 2 weeks or more, although I have not actually measured the vacuum pressure. The transmission control adjustments were done about a year ago when the vacuum valve at the injection pump was replaced. It was OK for a while but now gradually this clunk has become a problem. I think I may try a different dealership. The local MB dealership was a relatively new start-up, the sold out to one of the old established deaalerships from Dallas. Point is, I am not sure they have an old-time diesel tech who is thouroughly familiar with this.

If, after transmission vacuum adjustments, this is still a problem, I may try a boneyard differential. Can that be done by a reasonably well equipped non-MB shop ? Are special tools required ? Also, for an early 84 300D, is that certain to be a 1:3.07 differential ? Some of the MB manuals do not seem to agree on the ratio. Many thanks for all the info. Mercedesshop has been a tremendous wealth of information for me. Happy New Year to all !

The vacuum to be concerned with is that sent to the modulator. It has nothing in common with other systems except its source. If you tee to this line at its rubber connection near the oil filter housing you should see high vacuum anytime the throttle is at idle position. The relation of this vacuum to your clunk should be evident.

I think all turbo diesel differentials had the 3.07 ratio except the 85 models which went to 2.88, if memory serves me.

While installation is rather simple with no special tools necessary, I always recommend a good independent for value. My techs can exchange one of those differentials in less than two hours which makes it easy for us to only charge the warranty flat rate which I am guessing to be close to 4 hours. There are a couple tricks that facilitate such quick efforts and without experience a general shop might spend half a day and expect more for working on an "exotic".

Good Luck

[Edited by stevebfl on 01-01-2001 at 11:44 AM]