Oh, Oh . . . A Rear End Whine

Whine at High Speed
This started about 1 month ago when we took at 150 mile trip. On the way up, the whine was low but easily audible. On the way back, it was louder and it peaked at higher speeds.

A few weeks later, we took another 200 mile trip and the whine got much worse, so much so, that at around 80mph, it resonated in the car's cavity and would almost drown out our conversation! Not good! I was convinced that it's a rear wheel bearing. And from the sound inside the car, it was the RIGHT-REAR WHEEL BEARING!

This is where the story gets interesting. . . the diagnosis and repair of the "whine"! Even though the noise was located within a known area, it was not easy to find what component had failed!

Diagnosis
The car was put on a hoist and run in gear. My '94 S500 has full-time ASR so you can't run it much above 30mph on a lift before the ASR takes over and shuts the rear wheel power down. But we thought that would be enough to be able to hear where the whine was coming from. WRONG!

Listening the the rear wheels, first left, then right gave absolutely no noise! I had a hard time w/ that b/c it didn't make sense. . . except that there's no 'weight' on the wheels other than the wheel-weight itself.

Listening to the differential showed the same results . . quiet as a mouse! However, moving forward, the drive shaft [d/s] made a sort of 'clunking' sound, so it had to be that! The D/S was removed and sent to a local drive-train shop for repair and re-balance. There's a key bearing that allows the shaft some flexibility so it had to be that bearing that went bad! WRONG! It was returned, re-installed and the whine was still there! Price tag, about $350.

So now, we are in a "guessing" game . . . so a master engine and car builder was consulted to see what he thought. An elaborate audio stethoscope was employed where each wheel had a 'monitor' coming into a switch-box where each wheel's noise could be heard separately in a set of headphones. Sounds like it should work. After the road test, the tech was convinced that it was the LEFT WHEEL BEARING! So the wheel bearing was replaced . . . those who have replaced one, know that it's not an easy task! After replacement, the car was again tested with the same results! Whine hadn't decreased even 1 dB!

So now we're left with it being either the right-wheel bearing (my choice) or the differential. The latter was the choice of the shop owner since he first heard it on a test drive. At this point, I was game for almost any solution so a used differential was sought.

Parts Search
I've purchased Mercedes parts from Eddie Alberini's ebay store but he has recently closed the store due high fees. Contact him at 508-244-0593 anytime for your parts needs. He has high quality parts at reasonable prices. Remember to check with him when you need parts for your S-Class.

When contacted for the 2.65 ratio differential, he had one. The only problem, he's in Massachusetts and I'm in California. But he has always given me reasonable prices and this was no exception. The differential was shipped via UPS with expedited handling and it arrived in three (3) days.

When the old differential was removed, placed on a bench and rotated by hand, you could plainly hear the 'clunk-clunk'. Definitely this was the failed component and it was, most likely, a failed bearing. So we were confident that the whine would be history upon re-assembly of the car. And it was!

So even though it appeared that fixing the car's whine would be very straightforward, it certainly was an eye-opener.

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