Whining C140 rear end . . . - PeachParts Mercedes-Benz Forum

JimF · #1 06-25-2010, 01:27 PM

After my '94 S500 cpe has been "perfect" for all of these years, a 'whining' noise started to develop a few months ago.

It got progressively louder on trips until the last trip where it was a real howler! At certain speeds of 62 and 82 mph, it really resonated in the car like a speaker in a hollow room getting the room to resonant. Could hardly hear yourself talk!

It certainly appeared to be coming from the right rear . . a worn wheel bearing per "my" diagnosis. One tech thought it was a worn wheel bearing on the left side. Another agreed with the left side diagnosis.

When it was put on the lift, the drive-shaft [d/s] made a fair amount of noise and the supposed wheel bearing noise could not be heard. So it HAD to be the d/s. The universal joint made sort of a 'clunking' sound. The flex discs were perfect. So it was removed and sent to a drive train shop for repair. After repair and re-balancing, it was mounted . . . still the same noise!

The shop had a new set of MB wheels so the next attempt was to swap the rear wheels w/ this new set and check for whining. No change, still there. But a easy try to see if it was the wheels and/or tires.

Next, using a "stethoscope" attached to each wheel, the new diagnosis was the left wheel bearing. This was confirmed by another tech, so two votes. As many of you know, replacing a MB wheel bearing is not for the weak! After it was replaced, no change in the whining noise.

So it's either the right wheel bearing or the differential . . . at this point, I voted for the differential. Got a used one (2.65 ratio) one from "S-Class-Eddies" [click the link in my signature and go to the "LINKS" section of my main MB page at the bottom] parts shop for a very reasonable price!

Shipping to So Cal wasn't cheap but it arrived, was installed and problem gone! Turning the old differential by hand, revealed the problem which most likely is a bearing.

Fortunately, it's not a very common problem and you can see that's it's not that easy to diagnose . . . . .

tbomachines · #2 06-25-2010, 02:46 PM

Did you have any fluid leaking out at all? Usually diff whine is due to internal wear on the gears, allowing for play between them. Low fluid exaggerates the rate of wear significantly.

JimF · #3 06-26-2010, 01:57 AM

It was dry . . . and the fluid was at the top level. . . so all should have been ok.

Also we drained the fluid out and it was brown in color, not grey. Grey indicates gear wear.

So it appears it was due to a worn/damaged bearing b/c of the above plus the fact that it came on relatively suddenly. Worn gears would have progressed over time, gradually becoming louder as the gears wore down.

Anyway, it's fixed now and runs very quiet . . . just the way I like it!

emerydc8 · #4 06-26-2010, 02:35 AM

Nice write-up. It's a pleasure to read a post where the problem and solution are both presented. I presume you're not planning to replace the right rear wheel bearing any time soon? I heard they are a bear too.

JimF · #5 06-26-2010, 03:05 AM

Tnx emery . . nice to see you post in the thread.

Well, it was easy to write it up when it's fixed. . . but during the "what-the-hell-is-wrong" phase, it was a panic!

I told the shop owner that it would be my luck to be the right wheel bearing after the diff was installed.

emerydc8 · #6 06-26-2010, 03:52 AM

Reminds me of that old saying, "Did you ever notice that 9 out of 10 times, what-the-hell is the correct response."