LSD? Something else
 

Took the '88 930 out this weekend. Second drive since I changed the transmission oil out with Mobil 1 Devlac (75W-90W) and for the first time I noticed a shuddering sensation (no noise) while starting in first gear but only while cornering. Ddin't matter if it was warm or cold. It's definitely okay in straight line starts though.

I did some searching and saw that this might be related to the gear oil but Mobil 1 is specified for just my application. Thoughts?

Clutch chatter due to cracked rubber clutch?

Would a cracked clutch manifest itself only while starting out in first and only while going around corners?

That's most likely the limited slip you are feeling. What gearbox oil was in it before the change?

JR

I had that problem on my former '87 930 with Mobil 1 gear oil. Switched back to Swepco 201 and the shudder went away.

Hey JR no clue but I may be able to find out. So I guess in trying to do a good thing I screwed up....Wouldn't be the first time just ask my wife....Can I add an additive that will remedy the problem or do I need to drain and refill? I had debated using Swepco but searched here and was pulled to the Mobil 1 Devlac.

I know nothing about the Mobil 1 product you used. Off the top of my head, I'd rather change the fluid again than add an additive. I know a guy that used to recommend adding an additive that GM used to offer for their LSD axles, but I'd hate to create a witche's brew and hope for the best.

If it were me, I'd ask someone that deals with these things on a daily basis. The guys at Guard Transmission come to mind.

JR

FWIW,.....Delvac, while an excellent lubricant for the G50 transmissions that contain B-W syncromesh, doesn't work in Porsche gearboxes that uses the balk-ring design (901-915-930).

You really need to be using Swepco 201 in that thing. :) :)

Thanks Steve!

One of the hazards of using the search engine is that sometimes you get the wrong answer. I spent a day searching what to use and even asked specifically on a related thread. I was steered away from the Swepco and towards the Mobil 1 with Devlac. Actually it was probably more of a toss up.

Swepco is on the way then.....

I've got a G-50 with limited slip. I thought the shudder as I make a left turn coming off my street when cold was something I had to live with.

Do you think Swepco 201 is the correct gear oil for this car and would make a difference?

This is a very important distinction that I think a lot of people don't realize or understand. The Borg-Warner synchro design used in all of the Getrag transaxles is a very different beast than Porsche's own design that was used in the early cars. I see a lot of shifting problem on both cars fixed by using the proper lubricant. These two different designs have different lubrication needs mandated in large part by friction levels of the lubricant.

As Steve has said, Swepco for the 901, 915 and 930 gearbox. Any number of natural gear oils would be equally acceptable, though Swepco really is the best. In absence of a Swepco budget, Walmart's Supertech is a very good lower cost alternative. It's from the same refinery that does all of Exxon-Mobil's oils. It's good stuff.

For the G50 and other Getrag variants, the Delvac is very popular these days. However, with the number of synchro problems that I see on a daily basis, right now the only lubricant I recommend to my customers is the Shell Rotella gear oil that Porsche is selling. I know $80 a gallon seems a lot, but if it can put off that $4000-5000 rebuild on your 996 a while longer it's worth while.

Is an LSD additive required in addition to the Swepco?

Nossir, not unless you have a case of "stick-slip" going on. That calls for an additive.

The #201 product will be perfect. :)

kilodawg, when you get ready to drain it, catch it the original bucket and hang on to it for a while till someone with a G50 is going to change his gear lube out on his G50 without the lSD. I would not think that you could have done any real harm to the other. Then he can fill his up with yours and all be happy in the kingdom,.

Just add the GM additive.

I find the ZF starts to chatter after about 10k miles, so that's when I change out the gear oil.