Noisy Rear Differential in '72 4.5 - PeachParts Mercedes-Benz Forum

HwyStar · #1 10-26-2022, 01:21 AM

The rear dif in my '72 has become noticeably noisier over the last couple of years. I've changed the fluid (most recently to a heavy 140W gear oil from Red Line (their recommendation)) and its still loud. (It makes a werring noise).
Can this dif be rebuilt or does it have to be replaced with a (hopefully) good used unit? Any help/advice is greatly appreciated. Thanks.

Todd Miller · #2 10-26-2022, 06:10 AM

Here's a link to a picture of it as a parts diagram.https://www.niemoeller.de/en/w108/w108/B057/24

You can call Alfano Motors, locally, and see what's available through MBZ. It takes special MBZ sockets to get one apart.

There's a complete axle on ebay, down in Valencia, but IMO, ridiculously priced. You might be better off sourcing from a wrecking yard on your own, or buying a donor car that's in bad shape.

Tomguy · #3 10-26-2022, 04:56 PM

I am not going to claim to be a fluid expert, but wouldn't a thicker viscosity oil cause faster wear and more noise?
Have you tried a 90w GL5 gear oil (or 80w90 GL5 oil)?

rumb · #4 10-26-2022, 05:53 PM

I have a complete rear axle from 6.3 available. I dont know if it fits but it looks similar to the diagram.

If you were to rebuild one I would suggest reading the manual to see how difficult it may be. Item #21 are shims that may take special equip of procedure to set correctly.

Todd Miller · #5 10-26-2022, 07:31 PM

I don't know anything about working on the rear axle assembly, but based on the parts diagram, I'm wondering if the pinion and it's 2 bearings, which are likely what have failed in the OP's axle, can be extracted out the front, new bearings installed on the pinion shaft, and the the thing re-assembled successfully, using the same shim stack that it was built with? There's a whole thing about pinion depth in ring gears, and using prussian blue to set them up, but again, this is not my skillset.

I guess if the pinion could be extracted with the axle in the car, you would also be able to inspect the teeth of both the pinion and the ring gear. If you found pitting on either, you'd know you were completely screwed, could stop the job there, and start looking for a good used axle assembly.

There are also bearings on either side of the differential assembly, and of course those could be failed as well.

Tony H · #6 10-27-2022, 01:02 AM

I used to have links to an R&R writeup. I will look and see if I can find it.
Edit: here it is https://www.sl113.org/forums/index.php?topic=5958.0
I used to find 3.27's in the Pick n Pull for like $150. I got one over my lunch break once. Those days are long over.

Todd Miller · #7 10-27-2022, 01:36 AM

Thanks for posting that!

And yes, those days are long over!

HwyStar · #8 10-27-2022, 12:14 PM

So, buying a used unit with no background info (i.e. mileage) seems like a huge gamble to me. Is there no known shop that could rebuild mine? (I'm in Central California but could drive the car to S.F. bay area or L.A.). Thanks to everyone.

Todd Miller · #9 10-27-2022, 01:29 PM

As I mentioned in your thread on Benzworld, the Mercedes Classics Center in SoCal.

Tony H · #10 10-28-2022, 12:14 AM

You might be able to find a European oriented shop to work on it.

HwyStar · #11 10-28-2022, 07:58 PM

Thanks for your response. I don't know if the 6.3 rear end was the same as a 4.5 or not.
But I know mine has a 3.27 ratio (its stamped on the bottom of the dif). Nice offer. Where are you located? Do you know how many miles are on yours?

Tony H · #12 10-28-2022, 09:45 PM

A 6.3 axle is not a direct replacement-it does not accommodate the rear compensator/spring and it has attachments for the anti-dive which need mounting points on the body. Also the ratio is too low for a 4.5-it will be quite sluggish.

cleeves · #13 10-29-2022, 11:29 AM

My W115 differential became noisy, and so I ordered an as-is differential with a different casing (but same gear ratio) on eBay for a couple hundred bucks, and a shop was able to swap out the pinion - and the noise went away. They found some weird pitting / wear pattern on the original pinion. Didn't cost me too much to have this done.

-Henry

HwyStar · #14 11-03-2022, 07:32 PM

Thanks for all thoughts and messages... I have emailed the Classic Center and so far crickets. Would really like to correct this problem.

Todd Miller · #15 11-03-2022, 07:39 PM

Did you call Rizzoli's as I suggested? Back in the day, they would have had the tools for doing this job, and a tech or two would were skilled in it. They may still have the tools, and may still be skilled/interested in doing the repair, or at least going far enough to take out the front cover and pinion, inspect the pinion bearings and pinion gear, and the ring gear.