Mercedes: W124 Rear end rumbling, wheel bearing, rear camber

Question
QUESTION: Hi
My car is a 1994 W124 2.8. It just had its subframe and control arms replaced due to an accident. The problem is that now there is a LOW frequency rumbling sound starting at around 65mph. @65mph there is an intermittent howling just like the washing maching just started spinning. Then the rumbling becomes continuous @75mhp plus. The noise is then easily mistaken with wind and rough road noise except it has a lower frequency.

I guess it's either the wheel bearing or the diff, do you think that make sense? By the way, on the crash impacted side of the diff it seems to be covered in grease, I'm not sure if it's from a leakage or it's just some random grease.

Please help... MANY THANKS

ANSWER: Hello Roy,
If this vehicle has independent suspension, I would suspect a problem with the wheel bearing or U-joint in the axial.

If you  are using the same wheel and tire... it could  in the tire. The re alignment should have been done on a four wheel machine. If the toe in on the back wheel is really off it could be a scrubbing of the tread.
Feel free to provide additional information about what parts were replace on the vehicle.
Good Luck
Rob

---------- FOLLOW-UP ----------

QUESTION: Hi
First thank you for the quick answer!

All 4 tires have been changed to new ones. Alignment was done on a 4-wheel machine. However rear camber could not be altered. I'm asking them to re-check the rear toe today.

The rear suspension is multi-link independent. Which U-joint do you mean? The one on the main shaft? Or the ones driving to the wheel?

Answer
Roy,
Was the wheel bearing replaced during suspension repair. If not it is the first possibility regarding a vibration. I do not know if this bearing is adjustable with the axle nut or not, but that should be checked even if it it new. A wrong tension on the bearing could cause it to vibrate. If it was not replaced, I would probably have it replaced.

I cannot remember if Mercedes uses a rubber disk on the axle joints or not. The main drive shaft on my car uses these disk in place of a conventional U joint with bearings.

It is possible the axle shaft was displace during the impact and damaged some of the needles in the bearing on either of the U joints on the axle. If the have a grease fitting on the joint you may want to have the joint greased. It may be a case of dry needles.

In a conventional joint, you can sometimes see the play by placing the vehicle on a rack and have someone try to rotate the wheel back and forth against the parking sprag. With a hand on each side of the joint you can feel the rough place. Sometime just shaking one hand against the other will detect a bearing about to go bad.

Secondly, if the drive shaft was driven inward during the impact, there may be some binding in the differential chunk. Thus grease leaking around the bearing seal. I trust you have had the dope in the chunk checked.


Let me know if you have any further questions.
Rob