Center driveshaft bearing
 

Hey guys sorry to post again so soon, but I’m need of a little urgent help.

I think my driveshaft center bearing is going out. My 83’ 240D 4-spd makes a pretty loud clunking noice when I’m driving, and when I push the clutch in the noise goes away.

I crawled under and looked at it, I see the rubber bushing/bearing and I can move the shaft around within the rubber, I.e. the rubber allows some give. Is it supposed to move a little like that? It moves like a bushing should but I know it has a bearing in there.

Also, how would I be able to tell for sure if that’s my problem? The noise kinda just started suddenly. It’s worse at slower speeds and goes away mostly at high speeds.

Thanks

Disregard previous post. I located the noise to the diff. Somethings obviously very wrong. I’ll have to drain the fluid and inspect it for metal. I’m expecting to see a lot.

Not sure how the clutch pedal would affect the differential, but ok...

The center bearing mount does allow the driveshaft to move a bit. It's a rubber "bellows" looking piece to allow some lateral movement. What isn't normal is if the driveshaft just flops around, usually means that the rubber has rotted and the bearing is just flopping around unrestrained.

If you know the popping noise is coming from the rear end, don't forget to check the CV joints on the half shafts. If the boots have failed, or the grease has run out, they can make a heck of a racket when they fail.

Maybe the rear diff mount collapsed.

Sixto
98 E320s sedan and wagon

I don’t think the clutch has anything to do with it, I’m just saying when power is applied to the drivetrain, the noise persists When power is removed, the noise goes away, regardless of speed.

The center bearing moves exactly as you describe it should in proper working order. “Bellows” is exactly what it’s like.

I jacked the rear wheels off the ground, let it in idle in 3rd, and stopped the movement of each wheel independently of the other, and the noise didn’t change. i.e., the noise was still there when both pairs of CV joints were stopped at separate times. So could it be those?

Could be the diff mounts? I’ll check.
Could a tooth of a gear have sheared off?

The sound is prominently coming from the diff. :/

Are your CV boots looking okay? You should inspect them for cracks or tearing. Sometimes they may look okay but if you squeeze them some fluid may find its way out of the shaft. And if you see any of those symptoms, you most likely have an axle that needs to be replaced. Sometimes a torn CV boot can be replaced and the axle will be restored, but only if you catch it early on before you hear any sort of noise from it. When a CV joint loses its lubrication, it basically becomes a metal on metal joint. And once you have metal on metal, the joint will quickly wear itself out beyond reasonable repair. Also when this joint heats up after driving, it will cause all kinds of strange sounds coming from the rear end which I think may be your case here...

Not too long ago, my 82' 4 speed had a torn boot in the right axle that I was aware of. I think during the previous ownership it had ripped and leaked most of the grease out. I let it get worse knowing that the axle was most likely a goner anyways. The right axle of course started clunking around after a year or so. I distinctly recall pushing in the clutch and coasting caused the noise to die down. I ended up replacing both rear axles with some aftermarket ones. The noise went away, and the car drove nice and smooth after that. But boy some of those aftermarket axles are absolutely junk. Check those CV boots and let us know what you find.

Pushing the clutch to have the sound goes away makes sense to me, something is only unhappy under load. U-joints in trucks often do this.
The center bearing/bushing going bad may cause a vibration, but shouldn't cause a clunking. Mine was completely GONE, the bearing was almost seized and was spinning the rubber with no clunking.

Check the u-joint in the center and the flex discs for cracking and play. If a flex disc comes apart on you while driving, you'll likely destroy your driveshaft, check that immediately.

If the rubber on the center bearing is still intact, I'm doubting that is the problem. My personal thoughts, due to personal experience, a worn axle cv-joint is likely.

Raise the car with the rear suspension suspended. Do the cv-joints have any odd angles or shapes? Try a rotation test on each wheel and see if they operate smoothly. Mine had a "double-bend" at the cv-joint and changed shape with rotation.

My center bearing looks OK, like I said the noise is 100% coming from the axle area.

The boots are old and cracked but I don't know if they're leaking. I'm a huge fan of checking the simple and cheap stuff first so I'll begin with those and the mounts.

This might be a good time to go ahead and do a diff swap (check my other recent post about the Found 190d) to the ratio I want, and at the same time restore/replace the axles and CV joints