86 951 Driver

If there is play in the transmission mount what kind of a noise would it make? would it get worse going around corners.

GreyDog

Try changing oil in the trans, especially if you have LSD. Mine made noise as the lube was cooked. Otherwise may be CV's?

JohnKoaWood

if the mount is totally thrashed you will get gear noise, worse on hard cornering, and ultimately will break CVs on cornering...

jack the rear of the car and push the trans side to side... it shouldn't be easy to move, or move very much.. if it moves a lot or is easy to move your mount is trashed...

PorscheDoc

Here is a little more information to help.

Car has a noise in the rear end that sound like wheel bearings grinding. We initially thought it only did it under boost, and with a bad turbo with a chewed up impeller blade, thought the noise might somehow be transmitted through the exhaust from the turbo being out of balance etc. Drive around normally without any hard/sharp actions and you will never hear the noise.

1. Jeff installed new axles, no change

2a. We swapped the turbo for a rebuilt unit since it had to be done. no change

2b. After test driving the car after the turbo swap I had a little more one on one time with it. I could get it to make the noise any time the rear end squated excessively. Hard acceleration, just punching the gas pre boost, hard/sharp slow corners, etc.

3. Figured....classic wheel bearing noise, especially after getting it to do under turning. Pulled the rear brakes apart, pulled the axles, spun the hubs....crunchy. Perfect. Change the wheel bearings on both sides. Noise changed maybe slightly, but still there. Bearing races were grooved significantly.

4. Trans mount does have play in it. Is it excessive? I don't think it is bad enough to make any noises, but who knows.

5. I believe in one of Jeff's post (either here or kcws) he said the transaxle was exremely low on fluid, which he either topped off or changed completely. I wonder if the bearings were starved of lube, but the transmission makes no noise when just driving around normally, braking, etc. Could the diff bearings be loading up under acceleration, making the noise? Not sure. There is some play in the output shafts, but not really enough to make the seals leak, which is usually the first thing to go before you hear any noise. IIRC when he bought the car, the shop that sold it had just installed a used tranny in it.

6. Shocks in the car are definitely shot. It floats like a cadillac. The rear end squats excessively when accelerating, so it needs new shocks all around for sure. Is there geometry out of whack when the car squats, causing the noise?

I hate recommending just throwing parts at a problem, but if it were me, I would get new shocks installed and maybe pull the trans mount and at least inspect it. If the rubber looks toast, urethane it and reinstall it. If the noise is still there after that, then I would swap in another tranny to see if that cures it.

86 951 Driver

I will say the Trans wasn't really that low on oil. It was filled enough that I could get it on my finger sticking it in the whole. I then changed the fluid and put in 3 Quarts of fluid basically until it was filled up to the top. Like it says on clarks garage. Now I know that Porsche put out a TSB a long time ago talking about something with the rear shocks making a noise.

Someone else has said that it might be a bushing on the torison bar carrier that could be shot?

This noise is driving me nuts.

I will say that before I got the car the transmission was replaced with a unit from Oklahoma Foreign that supposedly had 60,000 miles on it.

PorscheDoc

If that was the case, then I would put the transmission at the end of the list. If you could touch the fluid with your finger, then it should have had enough fluid in it to be ok.

JohnKoaWood

hmmmm, Docs analysis makes it sound like rear wheel bearings, I was having simmilar symptoms on my N/A.. finally got around to addressing the rear wheel bearings, and noise is all but gone.. I had symptoms changing when the rear squatted, accompanied by squeeking once per revolution.. drivers side rear wheel bearing outboard seal was damaged, I could see the damage before I pulled the hub!

My solid trans mounts days are numbered though.. it is driving me batty!

If there is the need for new shocks, replace them, they are cheap! ($)
If the noise persists, try a different trans fluid, I only use Swepco 201 now for a reason... ($$)
If the noise still persists, look at the wheel bearings... mine were howling / grumbling depending on speed.. and recently started squeeking in cold weather...($$$ and a PITA, but once you figure it out it is easy!)

But I could be wrong... how old are the TT bearings?

86 951 Driver

PorscheDoc replaced both rear wheel bearings. So that is definitely out.

Shocks are going to be next on my list. I guess I will just pick up some KYB's for now as they are better than the worn out 24 year old ones.

The trans fluid I used this last time was regular Valvoline 75w-90 fluid made for Hypoid transmissions. A lot of people on Pelican said that it was a fluid compatible with our transmissions.

I would think that maybe the trans mount is shot. My problem is I don't know if I could change that in my garage?

PorscheDoc

Yup replaced the rear wheel bearings and no real change.

TT bearings I would assume are original, though I would think they would transmit noise when driving the car at most speeds/rpms. Every bad TT bearing I have heard has been more constant, though nothing surprises me anymore, lol.

Not too often I get stumped on 944's.

The trans mount can be done in the garage on stands. Pull the passenger rear wheel, support the trans with a jack. Remove the 2 crossmember bolts to the body, remove the 2 bolts on the transmission to mount, take off the hose clamp for the fuel filter, and you can work the entire crossmember out the passenger side of the car.


Also, i would put on a set of koni rear shocks for now. Don't put on the cheap stuff, it will last about 5k miles. Then in the future, as finances allow, do the front koni conversion which is very easy.

JohnKoaWood

I have about 25K on a set of KYBs, they are coming off to be replaced with Konis when the Konis come off my 951... the KYBs are too soft for me on my N/A, they squat too much on hard accell, a turbo will make them full squat on hard accell.. Go Koni and dont look back!

The Valvoline fluid is more noisy in teh GB than the Swepco is in my oppinion, I have used it, but swapped it to Swepco.. now I ONLY use swepco, and just bought 2 mmore gallons as I am swapping the fluid in my N/A and adding an LSD to my 951...

Do the Trans mount, DON'T go solid... either OEM or semi solid from any one of the vendors... pick your poison...

FWIW I have my Konis set full stiff and have never gotten them to hit the bump stops, and am replacing them with Bilstein Escort cup coil overs...

86 951 Driver

I wasn't planning on ever going solid trans mount. I was thinking of filling my stock mount or using the mount that XSChop makes that is supposed to be semi solid. I think semi solid is the way to go. I don't know if his would transmit a bunch of noise or not.

Has anyone filled their stock mount and got more life out of it? My old 924S I did this too, but it was the early design mounts that don't really fail.

JohnKoaWood

CurtP got some 2 part urethane for his mount... is OK with the results.. shoot him a PM to get the info, I believe he got it from McMaster Carr...

I will be using the XS semi solid mount for both cars... stock gets floppy and solid is driving me insane!

86 951 Driver

Post your results with his semi solid mount. No one has really posted their results for it. I daily drive my 951 so I don't want a bunch more noise that comes with a solid mount.

supes6

I just did the urethane job on my stock mount... after a few weeks, I can say that it does not seem to increase the noise at all. But on cold startups in the morning, there is definitely a little more vibration - but just at idle. I imagine this will probably disappear in warmer weather though.

I also noticed that I get a squeaking noise when I pull into my driveway now.. probably from the urethane I'm guessing.

86 951 Driver

https://rennlist.com/forums/924-931-...lp-others.html

Is it possible that could be my problem?