Rumbling sound from differential (non-LSD)

[JohanE9]

Hi,

I’m in the process of bringing my 3.0 back to life after it has been sitting in the garage for almost 15 years. The car was gone through quite thoroughly before being parked, but unfortunately the long storage has left its marks.

One issue I’m dealing with is a noise coming from the differential (it’s not LSD). When driving in a circle – so with different wheel speeds – I get a clear droning/rumbling sound, very similar to what you’d expect from a bad wheel bearing, but it’s definitely coming from the diff.

What puzzles me is that this noise wasn’t there before the car was parked. Just before storage, the driveshaft was removed to replace the rubber discs and bearing, but otherwise nothing major was done.

Has anyone experienced something similar or have an idea of what might be wrong? Could it be a matter of adjusting play, or is it more likely wear from sitting for so long? Also, how available are replacement parts for these diffs?

Thanks in advance!
Johan

 

[eriknetherlands]

I no differential specialist, i just like taking things apart, ; this is what i know:

Standard diffs have a few bearings that are available through Walloth and Neesch. Replacing the side bearings is easy, they can be pulled out without opening the diff.
It does need to have the half shafts dismounted for it. In my side bearing I found a split (broken) ball retaining ring:

The bearing of the pinion wheel (the one in the direction of the drive shaft) isn't easy to replace as it requires a precise pre-load setting to be achieved through a crush washer that needs a precise torque and friction measurement in order for the pinion gear to match to the diff perfectly. The workshop manuals ("blue books") contain a detailed procedure for it.

Catalog picture 33/02 - BMW 2,5 CS - 3,0 CSL (E9) - Rear axle | Wallothesch

www.wallothnesch.com

So, one way would be to replace the side bearings leaving the pinion bearing untouched. Fingers crossed; it solves your problem, then it's an "easy-out".
If it didn't solve the problem, then perhaps the pinion bearings or the gear teeth itself are creating the problem.

Here's my diff, pulled apart. I went for the "fingers crossed" option, keeping the pinion bearings and crush washer.
I also see that i bought a O ring from the dealer - check via RealOEM which bearings and seals parts there are, replace all seals.

bearings.

 

[JohanE9]

Thanks a lot for your reply @eriknetherlands !! Much appreciated.

My thoughts are that if it were a bearing issue, the noise should be present all the time (is that correct?), but in my case it only appears when driving in a circle, or if I lock the driveshaft and turn one wheel by hand.

I’m also wondering if I might have tampered with (loosened) the crush washer (I assume part #4 in the W&N link) 15 years ago, and then just tightened it back without achieving the correct pre-load.

I’m a bit hesitant to take the diff apart without being certain that replacement parts are available. On the other hand, it probably isn’t a good idea to drive any longer distances without addressing the noise…

 

[eriknetherlands]

How's the oil? having too little, or bad oil also can create funny noises. Drain and inspect with a magnet for metallic particle(s). If a bearing fails you normally find debris. Fill untill it overflows the fill hole.

 

[Wladek]

Noise is while circling in both left & right directions?

 

[Dan Wood]

I chased a noise in the E24. I was sure it was the diff and had that rebuild / ratio changed. Noise was still there and it was sure it was coming from the rear. I changed the rear axle bearings (what a pain). Noise was still there and turned out to be the FRONT wheel bearings.
Lesson learned: Have someone walk beside the car to try to determine where it is coming from.