Clunk in front end at the track, any ideas?

[175K911]

Need to tear into the front end in greater depth, but here's what I'm experiencing:

On the track, once up to speed when I turn into a corner, I get a clunk. Just once, can hear it and feel it in the steering wheel. Won't do it again until I lay into the next corner in the opposite direction. Then same symptom. Never straight line, or on bumps. Never 2 consecutive lefts or rights.

Car specs:
86 911
ER polybronze on the a-arms
ER upper strut bearings
Ball joints and turbo tie rods
Bilstein inserts in Boge struts, valved to match 23/31 torsion bars
Tarett sway bar, nut plates welded in.
16x8 951 offset Fuchs with 225/50 RA1
All of the above new and installed over the winter, ran 11 track days with absolutely no issues. On the 12th day at Mid-Ohio, the clunk hit me so I parked the car on the trailer for the balance of the day. Nothing was changed before the run session when the cluck appeared. Car still appeared to handle fine, though I wasn't going to take any chances.

I have checked and rechecked every nut and bolt on the front suspension and nothing was loose. Ball joints have no movement. Wheel bearings are fine. Strut collar nuts are tight.

My thought is something is shifting, but it requires some reasonable force to cause it to happen. Then doesn't shift again until I turn in the opposite direction. So I'll start by pulling the struts out to see if the right front is bad, and check the right upper strut mount bearing. (I had a heck of time getting that one tight when I installed it.) Then the polybronze to make sure nothing has come apart. But at them moment it's all trial and error.

So I would welcome any thoughts y'all would have for me as I dive back into it. The silver lining in all this? I'm using this as an excuse to buy a lift to make it easier to get under the car.

[janz]

Maybe steering rack?

[widgeon13]

perhaps a broken drop link on the sway bar??

[175K911]

Steering rack is tight, doesn't appear to be any slop in the end bushings, and all the universals in the steering column look OK.

Drop links are fine, pulled them off to check them. Sway bar has no excess side to side movement. Even thought maybe the pivot brackets broke through the fender sheet metal, but all is good there too.

[911quest]

Make sure nothing is loose rolling around in the trunk.

[Bill Verburg]

something in the sway bar? links, bushes?

[JP911]

Wheel bearing(s) going bad?

[GaryR]

Even though you can feel it in the steering and it sounds like it's up front be sure to check everything out back also. CV joints, trailing arm bushings, bearings, etc...

[dfink]

I had a broken strut insert on the front that was very difficult to find. The inside of the insert was broken at the very bottom. Only way to find that one is to take the strut loose and see if there side to side movement in the shaft. May not do it fully extended so have to compress the shock just a bit and then check. Pain in the a** but if all else checks out OK it might be worth a look.

[david c.]

how about the needle bearings might be blown out on the steering column bushing up in the front trunk (above the gas tank).

[VaSteve]

Bilstein inserts in Boge struts, valved to match 23/31 torsion bars

Make sure that the big nut at the top of the strut (where you put the insert in) hasn't come loose.

[Zeke]

Originally Posted by VaSteve

Make sure that the big nut at the top of the strut (where you put the insert in) hasn't come loose.

Good thought, but I think even more suspect in that vein would be the top nut of the strut.

[175K911]

Nothing loose in the trunk
Sway bar drop links are fine, bar itself has proper lateral play
Ball joints were new Lemforder parts in April, and have no play
Wheel bearings were new in April too, and I pulled them out, regreased them to be safe.
Strut collar nuts are tight. As is the top nut.
Steering universals aren't making any noise or have any play.

In the rear:
Sway bar consoles are Wevo and triangulated for strength, all ok here
Spring plates are Weltmeister adjustable and everything back there is good too.

Plan for the weekend:
Check rubber u-joint at the rack
Pull struts out of housings to check everything there., including the ER upper monoballs.
Per GaryR's suggestion- I'll check the axles too.

Wow, after 20+ years of tracking 911's I've found one issue that has me stumped.

[Mothy]

I had a similar symptom - odd clunk or knock which only happened when there was a change in the torsional pressure of the car. Left to right or right to left turns, also when going over laybacks since the inside wheel hits first and compresses up = changes the torsion pressure on the front of the car.

Turns out it was the connection between my fuel tank and the body - clamped tight but the seal had deteriorated. Smallest body twist was making one of the clamps hold on then let go suddenly = clunk.

And the funny thing is you could feel it in the steering - not as movement but as sound transmission.

Might be worth checking - since everything else seems to be new or OK.

Tim

[175K911]

Originally Posted by Mothy

I had a similar symptom - odd clunk or knock which only happened when there was a change in the torsional pressure of the car. Left to right or right to left turns, also when going over laybacks since the inside wheel hits first and compresses up = changes the torsion pressure on the front of the car.

Turns out it was the connection between my fuel tank and the body - clamped tight but the seal had deteriorated. Smallest body twist was making one of the clamps hold on then let go suddenly = clunk.

And the funny thing is you could feel it in the steering - not as movement but as sound transmission.

Might be worth checking - since everything else seems to be new or OK.

Tim

Very interesting. Tank was out when the front sway bar nut plates were welded in. Didn't put a new seal in when the tank went back in. Most definitely worth checking, thanks.

[Bill Verburg]

I recently r&r'd the bolts that hold the sway bar to the chassis that was causing a clunk in mine