Experts: I'm going insane, I can't figure out this clunk/thud.

[Sail Boat]

Hey everyone-

This noise is driving me insane.

Whenever I tap the throttle, I get two successive soft clunking noises: one immediately after applying throttle and another when letting off. It sounds like its coming from the rear, but I can't be sure.

I've done a lot in attempt to remedy the situation. Originally, I suspected the differential, which was a 4.10 open with a standard bushing. I upgraded the diff to a rebuilt 4.10 LSD with a powerflex urethane bushing and made sure the halfshafts and diff bolts were torqued properly.

Noise persisted.

Next, I replaced the transmission mounts and checked the engine mounts. I even unbolted the flex disc to check the trans output shaft, but there was only a few millimeters of rotational play in either direction, which I have read is totally normal.

Noise persisted.

I felt discouraged at this point, since this indicated to me that the U-Joints, Flex Disc, or Center Support Bearing were likely shot. I decided to go ahead and replace everything in the drive line with a remaned driveshaft with serviceable U-Joints built by a BMW driveshaft specialist, a Febi Flex Disc and a Febi CSB.

The noise persists.

To be honest, I'm pretty confused. I replaced everything that is known to cause a "clunk" noise with throttle application. I'm starting to think that I'm trying to silence a noise that's normal.

Any other recommendations? Thanks!

[Mook613]

Is it only on lateral changes or do you hear it going over bumps as well?

Your diff is attached to your rear subframe which is held in place by some big bushings. I'm thinking that it could be those bushings, but if so I would think that you'd hear it going over bumps as well.

Other things to check would be to check for something loose in your trunk, perhaps in the spare wheel well.

[c0rbin9]

I had a pretty bad clunk even after replacing the giubo and CSB, turned out to be the CV axles. Check for play by rotating the wheel back and forth by hand.

[Sail Boat]

Is it only on lateral changes or do you hear it going over bumps as well?

Your diff is attached to your rear subframe which is held in place by some big bushings. I'm thinking that it could be those bushings, but if so I would think that you'd hear it going over bumps as well.

Other things to check would be to check for something loose in your trunk, perhaps in the spare wheel well.

Actually the car is super solid over bumps, all the bushes/struts/etc are refreshed. I only hear the noise when applying and letting off the throttle.

You know, that's a very good point... I've never checked the spare wheel well. I'll give it a look and report back.

[Sail Boat]

I had a pretty bad clunk even after replacing the giubo and CSB, turned out to be the CV axles. Check for play by rotating the wheel back and forth by hand.

will do, is there supposed to be any play at all?

[c0rbin9]

No play in the axle, there may be some play you can feel but it would be in the diff internals.

I bet you'll find that both CV axles rattle quite badly. Each axle has 2 joints which wear out and develop looseness. The CV axles are as much a part of the driveline as the driveshaft is, so if it seems to be related to throttle application, I'd bet that's it.

[jhaurimn]

I know that feeling of throwing parts at the car and still having the issue. Hang in there.

First make sure its not the spare wheel/battery/anything else in the trunk that could be loose.

Then Id be looking at your axles. Thankfully FEQ makes e30 axles for very cheap and they are easy to replace.

[c0rbin9]

I put FEQ axles on my car recently, and I'm hoping they will hold up okay, but if you'd like to maintain OEM quality for far cheaper than buying new you might want to look into an axle rebuilder in your area. For some reason they're often run by Chinese immigrants - we have one in the Houston area and they do a great job on hubs, driveshafts, axles, etc. Also FCPEuro sells OEM quality GKNs for $275 each, which isn't a bad price for those.

...assuming it's your axles.

[7pilot]

I would suggest that you experiment with adjusting the amount of preload of the driveshaft at the support bearing mounts and by adjusting the collar lock for the two sections of the driveshaft.
m

[Sail Boat]

I would suggest that you experiment with adjusting the amount of preload of the driveshaft at the support bearing mounts and by adjusting the collar lock for the two sections of the driveshaft.
m

Good idea.

Can you evaluate my install procedure? Before locking the collar, I bolted and torqued both the driveshaft and flex disc flanges. Then, I tightened down the CSB. What do you think I should try?

Axles are damn expensive so that's my last resort plan ATM... Not to mention, my car only has around 31,000 original miles so this kind of axle wear would be super premature. I'm going to check for CV Joint rattle/play tonight.

[johnt325ix]

Rotted out rear shock mount? Shock would be flopping around.

Sent from my XT1650 using Tapatalk

[jeffnhiscars]

Good idea.

Can you evaluate my install procedure? Before locking the collar, I bolted and torqued both the driveshaft and flex disc flanges. Then, I tightened down the CSB. What do you think I should try?

Axles are damn expensive so that's my last resort plan ATM... Not to mention, my car only has around 31,000 original miles so this kind of axle wear would be super premature. I'm going to check for CV Joint rattle/play tonight.

You have to preload the csb I believe 1/4" before yountighten the collar....and GKN is actually OE

[TobyB]

Long shot, but stick a 36mm socket onto your CV nuts where they stick through the rear hubs.
If they come loose, and the splines wear, they do just what you're describing.

But usually on your 2002, not your E30.

Easy to rule out,

t

[7pilot]

Good idea.

Can you evaluate my install procedure? Before locking the collar, I bolted and torqued both the driveshaft and flex disc flanges. Then, I tightened down the CSB. What do you think I should try?

Axles are damn expensive so that's my last resort plan ATM... Not to mention, my car only has around 31,000 original miles so this kind of axle wear would be super premature. I'm going to check for CV Joint rattle/play tonight.

As mentioned by Jeff. Your procedure is fine.
Loosen up the two bolts on the clutch support bearing and preload the bearing 15mm 1/4" towards the front of the chassis.

The E36 chassis also tend to display this issue quite often.

m

[ahlem]

Give various parts of your exhaust system a wedgie, especially anywhere that it's close to anything else. Torque changes can cause things to twist just enough to bang around. If you have a Go Pro, set it up to see how much your engine mounts are flexing when you accelerate and decelerate. Transmission mounts could cause a similar situation. You have a 5 speed or an automatic?