Rear suspension noise puzzler...

[fanaudical]

I've searched/read quite a few rear suspension noise threads this weekend; no real help there. I'm obviously missing something.

Our subject is a '75 Targa. it has recently developed a sharp semi-metallic clunk at low-speed bumps small-displacement bumps. This is most prevalent on the right side; larger bumps also creates the same sound on the left side. This seems to go away with higher speeds above ~30mph (but that may just be droned out by the exhaust). I rebuilt the suspension about 4 years ago and less than 10k miles on it since (new rear adjustable swing arm plates and rubber bushings, new shocks, new torsion bars, new sway bar bushings, the works).

Sitting on the ground there is still clearance between the torsion bar covers on the rear bushing cover plate. No signs of impact or rubbing. No signs of the swing arms hitting the cover plate bolts. The bushings that attach the sway bar links to the ball joint on the swing arms seem loose but that's about it.

I've sat in the car and had somebody bounce the rear end to see if we can reproduce the noise. All I get is shock noise - no semi-metallic clunk.

I've jacked the car up and inspected the following:

- Wheel bearings / wheel wobble - all tight

- I tried moving the swing arm about - all tight

- CV joints - no lateral movement of the axle in the joint, no noises

- Took shocks loose at swing arm - No wiggle in upper bushings when I push/pull on those. Shocks slide OK (at least as far as I can push them). Bottom mount OK.

- Bushings on the sway bar seem OK (but do have some lateral wiggle on the ball-joint bushings - see above).

- Brake hardware / shields all seem tight.

- Nothing loose in the engine bay or in the back that I can find.

Thoughts/suggestions?

Thanks for the help.

[Arlo911]

Any sway bar to gearbox mount contact? As the gearbox bushings age the mount/crossmember sags a bit and can come into contact with the swaybar. Itīs normally not that hard to see if there has been contact between the two.

[fanaudical]

That's a good thought. I went out and checked that - no evidence of scraping or contact. I've got about a finger's width of clearance between the sway bar and the trans mount.

[David Inc.]

Remove the sway bar and drive around to see if it makes a difference.

[phelix]

I’ll tell you what my suspension noise was if you promise not to laugh…

A few years back I installed new rear shocks, wheel bearings, brake discs, pads and shoes and hard lines on my 88 targa (now sold and in Australia). I was left with a clunk that I couldn’t find for almost three years. I check and rechecked everything. Disconnected the sway bar. Swapped shocks left to right. Put the old shocks back on. All to no avail.

Then one day I was underneath the car doing something or another and I idly put a finger into the hole in the banana arm. As you do. And something moved. I felt around a bit and eventually it dawned on me - it was a socket. Extraction required removal of the drive shaft. It turned out to be a 22mm socket that I had probably used as part of the bearing pulling/installing and somehow I had managed to leave it in the arm. After many years of working on cars I have a real mish-mash of random sockets so I didn’t miss this particular one. The resulting silence was glorious.

Hey, you in the back, stop snickering!!

[David Inc.]

Originally Posted by phelix

I’ll tell you what my suspension noise was if you promise not to laugh…

A few years back I installed new rear shocks, wheel bearings, brake discs, pads and shoes and hard lines on my 88 targa (now sold and in Australia). I was left with a clunk that I couldn’t find for almost three years. I check and rechecked everything. Disconnected the sway bar. Swapped shocks left to right. Put the old shocks back on. All to no avail.

Then one day I was underneath the car doing something or another and I idly put a finger into the hole in the banana arm. As you do. And something moved. I felt around a bit and eventually it dawned on me - it was a socket. Extraction required removal of the drive shaft. It turned out to be a 22mm socket that I had probably used as part of the bearing pulling/installing and somehow I had managed to leave it in the arm. After many years of working on cars I have a real mish-mash of random sockets so I didn’t miss this particular one. The resulting silence was glorious.

Hey, you in the back, stop snickering!!

Hahaha, well **** now I need to shake out my front control arms to see if that's where my noise is coming from too!

[proporsche]

make a video or sound re., so i could hear it....

Ivan

Thoughts/suggestions?

Thanks for the help.[/QUOTE]

[redridge]

What spring plates are you using, I think some say the sway away plates makes noises since the 2 plates are not sandwiched together by a bolt.

[fanaudical]

I am using the Rennline adjustable plates.

Loose debris in the swing arm is a possibility, I will check that out. - EDIT - Didn't find anything loose back there in the swing arms.

I will see about the video. ..

[bkreigsr]

my noise turned out to be the shock bottoming out - after I lowered the car.

[fanaudical]

Sorry - No video yet - I broke something else and have been trying to get that fixed.

I do have the car at Euro height. I'm running Von's shocks front and rear and stiffer torsion bars. I don't think I'm bottoming out in back, but will look at that. I guess I should pull a shock and make sure the upper bump stop is still in place.

[fanaudical]

I hate those threads that somebody starts but never reveals the solution...

I finally fixed my noise issue. Turns out it was something loose in the engine bay after all. The lower wing-bolt and washer that holds the engine relay cover in place worked themselves loose and were banging on the engine tin on bumps. Not quite sure where they were hiding but I finally saw them during a pre-drive check. Replaced them - no more noise. I feel like an idiot...

[Mike Andrew]

Welcome to the Idiot Club. We can all probably claim membership if we've wrenched enough.

Glad it was a simple and cheap fix.

Now where's my smallest Channelock?

[ClickClickBoom]

What size are your torsion bars? I had an experience after putting larger T/Bs into my car.
On a very specific bump I got a really light click noise. Chased it all over the place. Turned out when the right front wheel hit the correct bump I could reproduce it. When larger T/Bs are used the car has less effective travel for the T/B but the strut insert still has its full stroke. The resultant clicking was from the T/B adjuster was drooping and clicking when coming into contact with the seat on the cross bar. It’s hard to nail the exact position of the noise because it only occurs on very specific type of bump. Jack up the front and check to see if the associated adjuster is firmly seated on the seat in the crossmember. If not you need stroke limited strut inserts. Elephant racing solved my issue with little drama. Bilstein has a stroke limited insert. This is super common with increased diameter roll bars.

[fanaudical]

Hmmm...I am running bigger TB's both front and rear and now you've got me wondering. I will jack up the front and check...

[ClickClickBoom]

Here is my experience:
The suspension upgrade!

The meat is on page 2

[fanaudical]

Well, that suspension noise came back and this time affected both rear wheels. This time it was the shock tower bushings (which haven't been there that long - only 5-6 years).

Anybody have any info on expected longevity of the rubber rear shock-tower bushings?

Are there any improved bushings over the stock Porsche parts?