Type 993 - LSD / gearbox question
 

Tried running a search on this but I couldn't turn much up...

I bought a G50/21 for my 964 track car (there's a suspension related thread on this) and I'd like to learn a bit more about the factory LSD, as I'm contemplating changing it to a Quaife LSD. Can anyone tell me what the lockup %s are for the factory LSD?

A bit of background on what the gearbox will be mated to... We are aiming for around 360hp with a conversion to 3.8l. Is the factory G50/21's LSD is sufficient for track work? The gearbox is bone stock.

Thanks for any input.

Stock for a /21 is 25/65 for the '94-95 ZFs or 25/65 or 22/40 for the later GUNs
These lsd are sort of weak sisters and will need to be rebuilt or replaced for track use. Guard transmission can do the rebuild w/ much better friction disks but it'll still be 25/65.

I'd recommend a PMS or GT 40/60 or 50/80 over any of the above or over a gear type torque biasing lsd for track use.

The factory beefed up their motorsports transmissions(the /3x series) w/ all steel syncros and billet shift forks on top of the gear changes and PMS lsd's.

Agree with Bill. A torque-biasing diff does nothing on decel (effectively open). A proper LSD allows you to trail brake much harder and deeper at the track, which makes a big difference in lap times.

My stock LSD wore out pretty quickly and I now use a Guard unit. I think it was a 40/60 but the shop tweaked it to be more like what they thought it should be. It makes a huge difference under hard braking to have a fully functional LSD. You'll know yours is shot when the rear end starts to wander all over on hard braking and you get wheel spin when you accelerate out of the turn.

Bill - What is a PMS or GT LSD, are these brands? My Google searches generate results relating to strange women having their period while under the influence of psychedelic drugs... I couldn't find a /31 unfortunately, so it's down to a rebuild or an outright replacement.

Have you guys heard of the OS Giken "Super Lock" LSD? I've seen it advertised in a couple of the past issues of Excellence, and was wondering if it is any good. It looks like a 2-way clutch-type LSD.

GT LSD = http://www.guardtransmission.com/

PMS = Porsche Motorsports http://www11.porsche.com/usa/eventsandracing/motorsport/racingcars/pmnabusinessinformation/contact/

I have seen the Giken stuff advertised, but have no experience with them

PMS - Porsche Motorsports the lsd's used by the factory in the RS, RSR and Cup cars
the 993 /3x series all used 4 plate versions, the 996/997 use 6 plate versions they are all 40/65s

GT - Guard Transmission sells a beefier lsd w/ a much stronger chrome moly case and tougher friction disks, they come 40/60, 50/80 w/ other options

both of the above ocasionally come up in the for sale sections, Tom recently sold a brand new PMS from his /32 and I just sold a rebuilt GT.

Tom can comment better on buying /3x as he bought a /32 in the not too distant past, they are available through the dealer net but they aren't cheap.

I've seen the ads for the Giken but thats all.

I hate it when that happens, Colin responded while I was typing

I type fast :)

Thanks Bill and Colin. Can you guys possibly share how much a rebuild by GT might cost? GT is doing a website overhaul. From web searches, it looks like the figure should be in the ballpark of around US$1,000 - 1,500. Is that about right?

Do any of these high performance diffs eliminate the shuddering in a tight reverse circle I get as a standard feature in my 91 turbo.

The stock 964 turbo LSD is 100% lockup on decel (or reverse), so a LSD with less decel lockup will shudder less.

I was going to post a question about the shuddering in reverse on my 91 turbo.
When I back out of my driveway especially when turning the car shudders from the rear. Only in reverse. So you saying this is normal for these cars?

I'm a fairly new owner of the car and my 87 911 didn't do this.
Thanks for any advice

Brian

Absolutely normal, and the easy way to know your LSD is still good.

That's a relieve!!!!!! I thought I had a problem.
I love Pelican, what a great source of information.

Thanks
Brian