Strange rear noise trouble.

[PorscheGuy79]

Alright, in a recent development my car has started making a quite noticeable "thunk" type noise stemming from the rear of the car when driving over harsh bumps in the road. I first noticed this over a long drive to Indiana on the highway, I had headphones in most of the trip and only just noticed this upon my arrival. I have rebuild the entire suspension system of the car a little over a year ago and most likely attribute this to a loose component of sorts, maybe a rear shock bolt. Any ideas on what could be causing such a problem.

Also, my friend guessed the rear shock bolt being loose and for the life of me I cannot remember how to tighten them on the upper mounts. I think they are reverse threaded but im not sure. Note: rears are Koni red adjustables.

Thanks for the input, I havent had the time to look at it yet so right now im just looking for speculation.

[Early_S_Man]

Matthew,

I have never heard of 911 rear shocks coming loose at the upper stud/nut. The threading of KONI shocks is normal M10 x 1.00 with 17 mm Nyloc nut, which is fine thread, that is the only unusual aspect.

Much more likely problem is worn-out, or missing bushing, or broken anti-roll bar mount ... they are notorioius for causing a clunk like you describe!

[tonythetarga]

Do you have a rear sway bar? Check the mounts for a broken weld. This is quite common and reinforced hangers are advised. As far as the rear shock goes, there is an allen head wrench that fits in the top while you tighten the threaded nut down.
Check your motor and tranny mounts. Easier said than done, it needs to be up on a hoist with a prybar used to check for excessive movement.

[john walker's workshop]

konis are famous for knocking noises. usually when they're old though. work each rear corner up and down repetedly to try to find the noise.

[tshore]

From the title, I thought this was going to be a thread about some unusual digestive ailment...

[PorscheGuy79]

My rear sway bar is a stock piece and I did look at them on a quick inspection though the car was still on the ground. My Koni's were replaced with the rest of the suspension about a year ago, same with the bushings.

[avi8torny]

I say it's the rear sway bar mount....

[moneymanager]

Have you tightened the cv joint bolts since you redid everything? THese typically need another shot after 100 miles or so.

[john walker's workshop]

sway bars often contact the trans mount over bumps.

[einreb]

Just say the word Matt and we'll all come back over and dismantle your car again.

[PorscheGuy79]

Originally posted by einreb
Just say the word Matt and we'll all come back over and dismantle your car again.

You guys really did clean house that day.

[PorscheGuy79]

Just a note, everything went well and the fix was done in the first 30 seconds under the car.

Culprit = loose lower rear shock bolt. Tightened to proper torque and the noise is completely gone.