Whining C140 rear end . . .

[JimF]

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 . . . . .