993Biturbo430

I have noticed on a couple of occasions, when taking a small round-about (tight turn), a rumbling/vibration noise (like something is rubbing against something else) coming from the back of my '97 TT. However, I don't hear that sound everytime (I went back round the round-about to check).
Could it be the LSD? Is it an indication of trouble?
About 9 months ago, when I sent the car in for the yearly servicing, I asked the mechanic to change the oil of the LSD (it had never been done, and the car was over 55,000 km). When I picked up the car, it was still not done; explanation they gave: it need only be done at 60,000 kms. I suspect that they did not have the proper lubricant in stock (they don't even have oil filters, I have to get everything and supply myself, even though they are the authorized workshop for the only Porsche concessionaire). Ah, the joys of living on a South Pacific island!
Any advice? And what lubricant do Porsche recommend for the LSD?

Thanks in advance

993Biturbo430

Anybody has some advice?

911/Q45

Can't give you an intelligent guess on your noise. I've had good luck with Swepco 201 gear oil and be sure and change the front differential fluid at the same time.

Droops83

Changing gear oil would be a good place to start. While it is true that 60K would be the normal service interval for gear oil, you also have to remember that it is 15 years old at this point, and should be changed regardless of mileage. Additives break down and the oil loses its properties over time.

I agree with Don on the choice of Swepco 201. We run it or 210 in all Porsche transaxles, including G50-based and 986/996. Excellent gear oil, and has limited slip friction modifiers in it already, no need for additive. I speculate that either the friction modifiers in your gear oil have broken down over time, or your shop put in the wrong kind of oil. Lack of these additives can cause the friction discs in the LSD to rapidly grab/release in a normal turn, even when they are not supposed to under steady throttle, possibly causing your noise. The friction modifiers make the oil a bit more slippery so this does not happen. If it turns out the noise is something else, changing the oil was not a waste since you likely needed to do this anyway!

In the Pacific islands you do not need to worry about notchiness in the shifting when cold, which is the only possible downside to running this type of thick gear oil in a G50-based tranny with conventional synchros. We don't have any issues with this in Socal either.

993Biturbo430

Don, Chris, thank you very much for your advice, I will follow it.

DM993tt

I'd start with wheel bearings.

budge96

+1 wheel bearings

993Biturbo430

Maybe that noise could come from a wheel bearing, but what are the chances, on a car with only 36,000 miles?

No HTwo O

True, but almost 14 years old (young).

Droops83

Could be, it's hard to diagnose an intermittent noise over the internet, but based on experience if a rear wheel bearing is bad enough for the noise to be that obvious, it's gonna be noisy all the time, even while going straight, and the noise will change with wheel speed. Does the noise happen only turning right or left, or in both directions?

Could also be a CV joint, get the axles checked out as well. But gear oil is easier and cheaper to replace than a wheel bearing, and sounds like it needs to be done anyway.

Start there and keep us posted.

993Biturbo430

I've finally had a chance to drive the car to check that noise again. It happens only on left turns; there's no noise going straight, or turning right. I remember that one of my wheels is not 100% true, but I don't know which one. So could it be a wheel bearing indeed, as suggested by DM993tt and budge96?
I'll replace the oil in the tranny and in the LSD as it is due anyway.

No HTwo O

Then I think the problem is on the right side of the car. Look there first.

ronnie993tt

I was advised not to change the diff/tranny oil since the factory stuff has additives you can't get in replacement product. Also my manual says it's a 50,000 mile change item. Streather says if it's synthetic, it's good for the life of the car???..

pstoppani

Synthetic or not, lube still deteriorates over time; actually, EVERYTHING deteriorates over time...

No HTwo O

When I got the Turbo in November, one of the first things done to "zero out" my maintenance, at 33k miles was a trans / front diff. oil change. Used Mobil Delvac 75W90. All is good.