RickBetterley

OK, this is not as weird as it sounds.
My track car (1995 993) has a new Porsche Motorsports LSD; about 12 track days on it so far.
In turns, the rear end of the car is making this obvious noise that is related to the speed of the car and perhaps the cornering force (it is hard to measure this as the sound is likely being heard reflecting off of tire walls, etc).
I think it is equal in both left and right corners, but again, tough to tell.
No sign of the noise on the straights or at paddock speeds.
Just back from 3 days at Mont Tremblant, and the sound was getting louder each day, but then, I was getting faster as the event went on.
Is it possible that this is the sound of the diff working and I shouldn't worry about it?
I would love to get some feedback here; am cross posting to Racing list as well.
TIA

Steve Weiner-Rennsport Systems

Rick:

Thats not ususual depending on how the LSD was setup.

What oil are you using?

RickBetterley

Hi Steve
Thank you for the quick response; I was hoping it would be a 'that's not unusual.' Your contributions are very much appreciated.
Trans oil is Mobil One Synthetic according to previous owner. Trans was rebuilt by Brian Coppan, who is very well thought of.
Are you recommending the Mobil One?

GabiOsz

My car always sounds funny if I drive having had LSD!

Mike in Chi

When I've lost a wheel bearing it kinda sounded like that (but with a friction kind of undertone), though more prevalent when turning in one direction than the other

JasonAndreas

Call Brian and ask him, depending on the type of syncros he used he might recommend additional additives and a Mobil 1 different (SHC) from what you buy off-the-shelf?

Steve Weiner-Rennsport Systems

Hi Rick:

Did he install steel syncros?

Did he put more preload into the LSD?

Call me when you get a chance,...

Blaine S

Hey Rick - it was great meeting you at Tremblant. Thanks again for the ride!

I too heard the sound you are talking about when we went out. It didn't just right to me and clearly increased under corner load.

I was going to say something when we came in but was just trying to keep my breakfast in place.

Maybe a wheel bearing? Steve and others will be able to give much better advice than me but I did hear it on most all corners, that you were taking oh so smoothly I should note, where I wouldn't think that the clutches in the LSD would be working hard at all. I guess the ring and pinion gears would be another story.

Greg Fishman

I am wondering about wheel bearings myself. Take the wheel off and remove the brake pads. When you turn the rotor/hub does it feel like it has gravel inside?

bgiere

The Mobil 1 gear oil available at Autozone,etc is not a good transaxle fill...you want Mobilube SHC . It is a diiferent formulation and has the additives for a LSD. Or you could use Redline 75w90.

bgiere

http://www.lufteknic.com/Merchant2/m...ode=lubricants

Dudley

Hi Rick, I heard the noise as well but I assumed it was wheel hop, hope it is nothing serious.

A little OT - Thanks for showing me the line and demonstrating how to drive the smooth line. Blaine is right on - you are smooth (and fast)! It was a great week.

The quality of people on Rennlist continues to amaze me.

ppressle

I have very similar symptoms in an old mustang with a new limited slip, I had used the normal differential oil and the diff made lots of ugly groaning noises in corners. Called the differential expert and he reminded me about the limited slip additive. That cured it right away.

I would call Mr Copans or your favorite tranny/diff expert to see what fluid they recommend.

tar6day

Rear half shaft CV joints??

RickBetterley

Although I have never been a fan of additives, it sure sounds like I should for this new diff - I'll get ahold of Steve Weiner as well as Brian to see what they think.
Thank you everybody