Phil Silano

OK folks, here is one that has been driving me crazy.

There is a definite dull metallic "clunk" from under the car when accelerating from a stop or after slowing down. It is clearly audible from outside the car. It is completely inconsistent. It may happen right at first movement, 5 seconds later or not at all. It's a little more prevalent under hard acceleration. Volume is also inconsistent. It may be soft pulling away from a traffic light and loud just getting into my garage. Very seldom in reverse though.

Sometimes there is a noise when coming to a stop under hard braking, but it is more of a rubber on metal or rubber on rubber sound.

So far we have tried;

Up on an alignment rack (wheels on the ground), in drive or reverse, hold the brakes (it's an automatic) hit the gas easy or hard - no noise. We did this for about 15 minutes then the shop wanted their rack back.

Jacked up the back (wheels off the ground) same routine, in drive or reverse, hit the gas - no noise. We even hit the brakes while the wheels were spinning, still no noise.

Swapped the prop shafts side to side no difference.

Checked all the bushing and torques on the rear suspension. Even pulled the right strut, just for the hell of it. I was hoping something would fall off. No such luck. Will pull the left one tomorrow. (hope springs eternal)

Changed the rear brake pads.

Changed the transmission fluid and filter.

Tomorrow or Saturday I hope to get under the car and listen to the central tube with a stethoscope and compare the noise to our 924. Should at least be in the same ball park if the tube is OK.

It only happens when the car actually moves. No other stimulus matters.

What next?? I'm completely stumped. Which means it's probably something obvious.

davek9

Something loose rolling around in your spair tire compartment?

Phil Silano

Tried that. Took everything out of the back, spare tire, tool kit, carpeting, made sure the battery was secure. No difference.

Bill Ball

How about tranny mounts (rubber and bolts)? Motor mounts? Did you check out all the suspension bushings, like the upper A-arm? Swaybar? Droplinks? Steering rack? Rear control arms? There are dozens of big bushings in the suspension.

Phil Silano

The tranny mounts look OK - Jacked up the tranny slightly and didn't see any problems
Engine mount look good
Ball joints (all four) look good

The following was done in April 2005;
Upper front A-frame bushings, the stiffer ones
Poly front sway bar bushings
OTT's engineering sway bar on steroids sway bar end links
Bilstein Eibach combo
new tie rod ends

I am a little concerned about the upper control arm bushing at the cross member frame. there is a bit of fore and aft motion when the link pin is out, but it is at the end of a long moment arm.

The conical washers at either end of the wheel carrier are also a bit loose on the pivot pin but I can't find any specs on how much play is allowable.

Other options?

Bill Ball

I think you observation of the control arms is normal.

Something sounds wrong about the way the hub carrier is assembled. Are the conical washers in the correct locations? They fit into concave depressions on the sides of the hub carrier. When snugged down, there should be no movement. You cannot even see the conical washer on the shock side. Here is what it should look like.

jon928se

It reads exactly like the balance weight inside the Torque Tube that has come adrift from its rubber friction mounts and is sliding backwards and forwards when you accelerate/brake hard enough.

Time for the TT to come out I would say

https://rennlist.com/forums/showthre...e+tube+rebuild

Post 47 of above thread shows a picture of the balance weight

Bill Ball

Good one, Jon! It makes a lot more sense than my suspension suggestions, as they should make noise on directional changes as well.

jon928se

It was the "It may happen right at first movement, 5 seconds later or not at all" comment that seemed to give it away.

Bill Ball

I've not seen it before. I was aware of the rather big weight and that it could get loose but I didn't know it would move that freely. I believe you've got Phil finally going in the right direction.

Steve J.

I've had the very same thing for years and decided it's the harmonic damper sliding around in pieces inside the TT. Check out the thread on my clunk.
Here is what it sounds like taking off.

daveo90s4

I'm with you on this Jon - exactly the sound I've heard on several 928s and in each case it was the 'dampers' in the central shaft sliding fore and aft under decelaration / acceleration.

Dave

jon928se

I've definitely seen or read someone opened up their TT to find all the bearings at the front of the TT and 3ft of unsupported Drive shaft.

I'ld like to know if anybody has decided to not install the balance weight after a TT RnR. I can't help thinking that unless you really want a very smooth quiet drive leaving it out will make a negligible difference. Thoughts ?

daveo90s4

Jon, my understanding is that it's largely to do with damping destructive harmonic vibrations along the central shaft. These harmonic vibrations can, if not dampened, very quickly result in the central shaft experiencing stress levels that result in it failing. It is my understanding that slinging the battery box off the rear of the transaxle also had some positive influence on reducing these destructive harmonics.

Cheers, and I hope all's well with you guys - quite some time ago since we had a few beers together in New Zealand at the pub in Herne Bay eh?

jon928se

It's a theory.... To my mind plausible if the weight was attached to the central shaft and spun with it, but it isn't. Mind you I never did quite get that being able to damp out harmonic vibrations in one thing by hanging a weight off something else part of my Engineering degree. Probably explains why I am a Structural Engineer - whenever it comes to stuff that moves or pivots around other stuff we tend to get a bit quiet and run away or just bolt/weld it down and make it all a bit (a bit = a lot) stronger

Sure is some time since the beer in Herne Bay. If you're in Sydney and fancy a beer ... you know where we are. I take it you sold the Civic ? or is it still there awaiting your return?