Torsion Bars Touch (Clunk) in Center of Tube??

[gregwils]

I know noises are really difficult to diagnose on a forum, but though I would give it a shot. I have a "clunk" in my rear suspension that occurs when there is a sudden lateral load on my rear suspension. In a slow sweeper, no noise, but an autocross type of transfer....."clunk". It has happened in a few other situations, but the autocross style weight transfer creates a consistent, repeatable clunk. It does not happen when the suspension is compressed and the car in going in a straight line.

Fast Freddie helped me isolate the noise. it definitely is coming from right below the rear passenger seat and seems to be coming from the center of the car. Fred, whose is a professional wrench, went over all of my work - almost everything is new - and we ruled out the swing arm, swing arm bushings (new ERP rubber), banana arm (new ERP bushings), shocks (rebuilt Bilsteins), sway bars, drop links, wheel bearing, motor mounts (we think). The noise is a heavy sounding metal on metal sound, no a lighter click. Again, it is coming from below the rear seat and not at the driver outer edge, more toward the center.

Our current theory is the bars may touch or bump during lateral loading and cause the noise. I found this post suggesting that the t-bars can meet in the center, so we are wondering if there could be a few thousands separating them, then they bump during a heavy weight shift.

If our theory is correct, seems like someone else could have experienced this? Has anyone every encounter something similar? Any other theories or suggestions? I searched, no luck.

[Flieger]

The bars are usually stuck in there very firmly. They don't see any significant axial loads so they should not be moving with any sort of speed. There may be flexing of the torsion tube itself. The anti-sway bar may knock on the transaxle. The transaxle will move around due to the rubber mounts. It could hit something.

[Flieger]

This is your stock '86?

[gregwils]

Thanks. Yes, stock '86.. Let me add one more thing. The noise surfaced after I did a bunch of rear suspension work. New trailing arm bushings, new swing arm bushings. The clunk is very audible. The ride height is approx 25" in back.

I know it's not the sway bar because I removed it and the noise was still present during a road test.

My bars are well greased and pull out of the center spline with no real difficulty. I understand that once the bars are loaded, they shouldn't be sliding around. I'm grasping at any reasonable theory right now.

[Flieger]

Are they normal rubber bushings?

[gregwils]

Yes, both spring plate and banana arm are new ERP rubber "stock" hardness. I know my banana arm bushings are fully seated and the bolts properly torqued. Chucked walked me through pressing them into place.

[RSTarga]

Are your axles tight? How about engine and gearbox supports?

[gregwils]

Yes, axles are tight. Engine and grearbox mounts are tight.

[ben parrish]

Transmission mounts? Had a similar noise years ago and that was it.

[gregwils]

Well, the transmission mounts appear OK, they're relatively new. However, I am going to order a set of four HD cabrio's.

The thing that is weird is that the noise occurs when the loads are lateral - side to side. Trans mount noise would probably occur with any movement.

[kidrock]

just throwing out a WAG....I know you and your wrench checked out your sway bars, but what about the sway bar mounts (where they are welded at the side rails)? Those things are somewhat notorious.

[martin.stafford]

I had a very similar problem with my '73. I had a clunk noise that would happen whenever I lad any change in lateral loading on the rear suspension. It sounded like it came from around the front of the gearbox. The problem could be replicated by jacking up the car and rocking on the left rear wheel. I went through a couple of visits to my mechanic to sort it out. As I didn't do it myself, I'm not 100% sure of how it all fits together, but...

Turned out to be a worn outer bushing(?) surface in left trailing arm. The bushing had been loctited in which fixed it temporarily but was too worn to hold and started slipping and knocking. I know it was the surface in the trailing arm, but I'm not exactly sure what goes in there - bushing/bearing/etc.

I had my trailing arms replaced and the problem's been solved for a couple of weeks now.

As we couldn't get hold of any steel trailing arms it turning into a huge job replacing them with SC aluminium arms, engine out, sway bar replacement, etc so it would all fit together again.

[martin.stafford]

Another thing on it - I assume the noise seemed like it was coming from near the gearbox mount as it was being transferred up the trailing arm. I was looking at inner arm bushings, gearbox mounts, torsion tube problems, etc.

If your problem isn't the same as mine, it could still be at the outer end and being similarly projected up the arm to sound like it comes from under the seat.

[gregwils]

Thanks for everyone's comments. I did examine the sway bar mounts and they appear to be OK - no cracks. However, I think I can safely rule them out too since the clunk occurred when the sway bar was completely removed from the car.

The trailing arm bushings are brand new - a few hundred miles. The noise is coming from the vicinity so anything is possible, but everything at the trailing bar mount fits together so snugly it's hard to imagine.

I would happily tear it apart again to get rid of it, but would not be happy to do all the work only to have the clunk reappear. Sometimes you have no choice.

[DohertyCM]

With all of the new bushings you are bound to hear some noise that is much more pronounced similar to putting solid engine mounts in.....but no one has mentioned the shocks...have you checked the bushings on them and are they good? Also does the sound have any type of cycles to it or is it like a hammer hitting the side of a boat?

[RWebb]

last resort = pull 1 bar out and glue piece of hard rubber on end

[RSTarga]

Does your car have Limited slip?

[gregwils]

Doherty - The rear shocks were rebuilt last year by Bilstein, the bushings are good and everything is torqued. No, not cycles to the bang, just a single clunk. Thanks.

Randy - If I understand you correctly, you are suggesting putting a piece of rubber in between the t-bars. Interesting thought, might try that.

RS - No, open diff.

Fast Freddie was telling me dealerships use remote sound sensors that they can locate at various places on a chassis or suspension to isolate noises. I did some searching and found that wired systems are about $100 and wireless are $300. I'm not sure I want to spend $300, but it would be worth $100 to quickly isolate the location of the noise. I can deal with wires for the few times this would get used, dealer would be a different story.