Rear end whinning in 240D

[Maddog]

The Rear end of my 240D whinning and i want to know what i can do to fix it. It sounds like it is coming from the rear differential. The car has 240,000 miles one it. What could this be?

[mbdoc]

If it is from the differential then the pinion bearings are to blame. You should be able to get a used one for $150 or so!

[tvpierce]

I had a wicked whine coming from the front, passenger-side of my car. I fixed it by making my wife sit in back.

(Sorry, I just couldn't resist)

Jeff Pierce

[JimSmith]

Maddog,

When was the last time the differential was drained and filled with fluid? Is there any evidence of leakage?

I agree with the suggestion that you plan on swapping out yours for another as once metal parts are damaged they do not "heal" but you might try changing the fluid to help damp out the resonances in the bearings or gears.

These noises in bearings usually arise when the surface of the rolling elements and the races become uneven enough for the load conditions to allow metal to metal collisions, and/or ball skidding. Both of these phenomena are precursors to more rapid bearing and gear tooth loaded surface failures.

I would give Redline's Shockproof Differential fluid a shot. At under $20 for the stuff and the 14mm Allen wrench you need (Sears) it may be sufficient to reduce ball skidding (thicker oil film) and metal to metal contact (thicker oil film), which reduces the source of the stimulation. The higher viscosity and additive package may also help reduce the resonant ringing you hear by increasing damping. But, any damage already done will not be undone, you will just slow down the rate of wear from where you are today and possibly reduce the audible symptoms you find objectionable. If the damage is enough to upset the preload on the bearing elements so much that skidding continues, well, the time you have bought is probably not going to be of real value.

I have used Redline gear lubes in my cars for over a decade and find they work very well at quieting gear noises, including differential whines. My 1986 190E 2.3-16 developed a nasty whine at 65 mph, a pretty common highway speed. It was about time to change the differential oil anyway so I tried the Redline Shockproof stuff and the whine went away. Not a scientific study on the subject, as another version of the product that was not "shockproof" might have done the trick too.

I can't tell what your actual situation is, but I would be inclined to change the fluid if it has not been changed in the last 30,000 miles. By the way, I am not affiliated in any way with Redline, I just like their products. The website if you are interested is:
www.redlineoil.com

Good luck, Jim

[omegabenz]

jeff thats pretty funny. I like that.

Jim, you are exactly right about the whine. There is slop in it.

My brothers differential does that because the old one broke and someone didnt align the gears when they swaped it, so it rings as the pinion comes off the spur gear like jim explained. We changed the fluid and it helped a little.

See every differential is a little different, they have to be shimmed side to side, so if you do get a another one, make sure that someone aligns it properly. My dad was explaining how to do it, but I forgot. I can ask again.

Id just change the fluid more. It can probably whine for a long time because the differential is one of the most reliable parts on cars anyway.

Good luck,

Austin

[michael rybikowsky]

how do you know it is the rear making the noise.If it is drain the lube,replace it with mobil syn,grease and drive it until it dies.Which will be around 2010.

[Bill DeWitt]

Jeff P. maybe you should check and see if the dog-house
is available tonight...bill