Ronin-951

I get that sound when the LSD in my pick-up locks and unlocks. Does everyone in this thread have LSD?

Jeff N.

LSD? - Yes.

86 951 Driver

LSD-Unsure still.

I have tried to figure it out, but still can't. If my rear end is up in the air and I spin one wheel in neutral the other doesn't spin. But when I gear they spin opposite. If one tire is on the ground and the other is in the air in gear it won't move.

I had PorscheDoc drive my car and he said it sounded kind of like CV's because it only made it when under load.

I would also like to add that the sound is only really present when I am WOT, or when going around a turn and giving it a little gas.

mikey_audiogeek

Nope.

Jeff, looks like we're on the same page. Can you do me a favour and check the output flange axial play on your trans? Mine is about 1mm and in the manual it says should be about 0.2mm.

Thanks very much for starting a thread on this - I had no luck searching on "clunk" previously!

mikey_audiogeek

No cage here. Doesn't seem to be exhaust either.

mikey_audiogeek

Hi, looks like we're in the same boat! I removed my rear sway bar completely and still had the noise. Noise was there with original torsion tube mounts and after installing Racer's Edge mounts.

in my case, it doesn't seem to be engine-torque-related which is why my money is on the handbrake assembly...

Jeff N.

Mikey - I just went thru a diffy rebuild and discussed the axial play with my gearbox builder. Net is this, there is a slight change it could be wear in your carrier bearing but it's more likely wear in the carrier bore itself.

My builder showed me how long the bores are for the output flanges and noted that over time there is wear in the bore and thats what's causing the axial play. His recommendation - unless it's causing a leak on the flange seal, don't worry about it. There is no fix short of replacing the carrier. Feasible on a non-LSD unit, just about impossible due to scares parts for a LSD.

My plan, drive it unit it croaks and then put either a Gard or OS LSD unit that replaced the entire carrier.

But, to answer your question - yes, my LHS side flange has a little play. I don't think that's the issue; I think the noise is too loud for that. My guess is something associated with the chassis mount points moving.

You'd have to explain to me why you think the handbrake causes the noise. I've had the handbrake drag a bit in reverse if you adjust it up too tight but no problems outside of that.

mikey_audiogeek

Me too.

Re the handbrake, well I'm obviously clutching at straws. I often get a clunk straight after the car has been on the jack with the handbrake on. YMMV.

mikey_audiogeek

From those symptoms: you don't have a LSD.

Cheers,
Mike

beebone

The noise came from front and rear as well. Still hijack?
Just try to narrow down the possibilities, I think probably are the noise kind of bushings. He can try to use some silicon lub the bushings, if he installed those bushings.

Jeff N.

OK. After a little studying of this thread, take a look at this. Working assumption is that we have the same problem. Noise a solid thunk when the rear suspension get's to a certain load point. We are not chasing creaking noises associated with delrin type bushings.

Not causing the problem:
- sway bar: based on Mikey's removal.
- roll cage: not everyone has one
- torsion bars: Mikey and 951Kaos have deleted them
- CVs: Not likely, mine are confirmed tight
- LSD noise: Not likely

Possible candidates:
- spring plate bushings; everyone has changed them but we seem to have a couple different kinds in use. We have polybronze in use, Weltmeister in use.
- torsion tube to frame mount bushings: everyone has changed them
- shock mount points: not mentioned so far all have modified shocks (coilovers or Konis)
- Other torsion tube mount points: upper "banana arm", this has to be tweeked when you pull the torsion tube apart, we have all done that
- Shifting of transaxle: less than clear but too early to rule this out. Does anyone have an "improved" factory mount (ie: filled) or a hard mount? Mine is new, good, stock.

Thoughts on this list?

Jeff

RENEE_J

Grab a hold of one of the axles and slide it outwards until it makes contact and see if that is the thunk that you hear. If so then at least it has been narrowed down to the area of the control arm. I have a clunk as well, however mine is caused by the unloading of the coilspring without having helper springs installed to take up the slack.

mikey_audiogeek

Good work, Jeff.

I changed to a urethane filled trans mount. No change.

Just a thought: Based on the noise, there is significant "stiction" involved. It is unlikely to be something that is free to move or has no friction, it is more likely to be something that is exhibiting stick-slip, or taking a set.
Anything that moves freely would tend to rattle rather than clunk.

I agree with Renee's test - this is what got me looking at the trans output flange axial (not radial) play.

samluke

My vote is tranny movement. Even with a new mount the tranny is fairly softly mounted. With agressive driving/higher horsepower the tranny moves a lot. You can grab the tranny and shake it by hand, to see how soft it is. The filled tranny mount is the way to go (in my opinion) it stiffens up the mount significantly without the risks associated with a solid mount.

I doubt its anything to do with the LSD. These are clutch LSD's there is no lock up.

Jeff N.

Richard - agree the trans mount is suspect but Mikey's is filled.