kjlindgr

Hey all.

I've noticed this a couple times (W211 E55) and am wondering if anyone else has experienced this. Every so often, when I'm backing up out of a parking spot or my garage, I'll get a seizable clunk that will come from the back end of the car. It doesn't happen all the time...but it only happens in reverse...and it only makes one "CLUNK" and then it's done. There are no other adverse signs or events that take place though...no jarring, tire screeching, leaks, squeeks, nothing...just the one clunk. It's on a perfectly smooth surface too so it's not suspension related as far as I can tell.

The first time it happened, I was all like WTF? Thought I hit something or ran something over. Now, I'm just curious as to what it is.

Could it be the diff doing weird stuff when unlocking? Something else weird pinion/ring related? Failing axles?

chiromikey

check your crossmember bolts and trans mount!!

kjlindgr

Hmm...never thought of that. Is it pretty common for these to work themselves loose over time?

chiromikey

it's not as likely that the crossmember bolts worked themselves out as it is that the last person who tightened them either forgot altogether or just didn't torque them properly. trans mounts (like motor mounts) can simply wear out.

kjlindgr

Thanks for the help. I'll get the car up in the air and check stuff out and report on my findings.