Thump from below

KenB · Post by **KenB** » Thu Jul 12, 2012 10:32 pm

Hey folks,

I've been noticing a thunk-thunk-thunk that sounds and feels like it is coming from below the floor of the driver/passenger footwell on any kind of relatively spirited turns to the left.

Not too long ago I did a whole front end rebuild with the subframe out. I have ST swaybars and urethane bushings on the connection between that and the LCA (forgot what those are called at the moment). Anyway, I investigated under the car and checked some torques and found nothing amiss, really.

Any ideas? I'm a little worried about it.

Thanks in advance.

KenB
1979 528i

scarey · Post by **scarey** » Fri Jul 13, 2012 8:24 am

Check the center support bearing on your driveshaft. If you grab the driveshaft and try to shake it side to side (with car properly supported, of course) you should see where the problem lies.

Good luck,

Scott

KenB · Post by **KenB** » Sun Jul 15, 2012 8:28 pm

scarey wrote:Check the center support bearing on your driveshaft. If you grab the driveshaft and try to shake it side to side (with car properly supported, of course) you should see where the problem lies.

Good luck,

Scott

Thanks, Scott, I can do that but a) a center support bearing that only makes noise when I'm turning to the left?, b) at the time I did the front subframe I also put in a completely rebuilt driveshaft, which now has less than 2k miles on it, and c) the sound seems to be closer to the front of the car.

Any other suggestions out there?

Eric Q · Post by **Eric Q** » Mon Jul 16, 2012 12:28 am

Does it make the noise only under acceleration? Try going in a straight line and accelerating hard from a start and see if it also makes the noise. If so, that should be the CSB.

GripGreg · Post by **GripGreg** » Mon Jul 16, 2012 5:51 am

If you installed a new guibo, did you leave the metal band in place till it was properly torqued down, & then remove the band?
If it was done outta sequence, guibos WILL wear out way, way too soon.
With a new CSB, a new guibo should of been installed at the same time.
I'm thinking that, maybe, if you only re-installed the old one, the same thing could happen?

KenB · Post by **KenB** » Mon Jul 16, 2012 2:47 pm

Wow, thanks for the thoughts, guys. It doesn't happen on straight-line sprints. I really don't think this is a driveline thing. Again, only on sprited moves *to the left*. If I just take a winding road nice and slow, I won't hear anything, but if I start getting slightly more aggressive with my turns to the left, thunk thunk thunk.

I will look underneath yet again but I'm still fishing for ideas.

Thanks again.

Ken

Eric Q · Post by **Eric Q** » Mon Jul 16, 2012 3:05 pm

Then try checking your sway bar mounts and strut mounts, as well as your bushing mounts.