So i spent the entire holiday weekend thinkig about LSD's. wife and kids are away at the fingerlakes . perfect for just thinking.
first of all i just cant buy in to that porsche cheaped out when it came to the lsd . i mean they have no problem using materials that cost more and then charging for it . look at ceramic brakes , they cost a fortune and folks just buy them . also back in 2004 and 2007 these cars were selling great and porsche could command any price they wanted . i also dont think they are stupid people.therefore however they built our lsd's was done for a reason. so it does worry me a little when we make changes to the lsd even the limited change that i made. everything is interconnected so i am not sure how we change the transmission or the brake bias etc.

the spin test thing i dont think means a lot other than that the preload is low (also matt explained some additional consequences ). however if the spider gear explanation is real i do not know at higher speeds what contribution (relatively speaking) spider gear and preload (belliville washer) have on clutch plate interaction. i mean porsche easily could have built an lsd with low preload (such that the clutch plates last a long time since lock up wont occur to readily) but with aggressive spider gear set up (such that at aggressive driving differential spin is limited)
anyway these are just some thoughts from a guy who is new at this . to make matters crazier i am going to put on my first set of track wheels and tires (ccw wheels michellin cup tires) all i really want is to get below 2:20 at watkins glen ,then 2:19 ,then 2:18 etc

 

stock 997gt3 on stock tires at the glen with decent DE driver is 2:16 - good driver stock car with Hoosiers is 2:10

if you are above 2:20 you are likely not using the LSD at all and until you actually start using it, it will be as the factory sent it out

once you start trail braking past the apex in #1, well past the 1st apex into the bus stop, to the apex in #6 and past the apex in #8 for a few DEs and then get your times into 2:15 range, you will not realize you have a problem, because you won't have a problem - the LSD will be 'functioning" or not activating at all - it is only when you do the above, that your LSD will go and then the next lap when you come into the bus stop at 150mph, brake at the 3 1/2 marker and try to trail it past the first apex will you realize you have a problem

WG also doesn't have the lift the inside wheel 2nd gear type of turns that begin to shred the inner spinning rear wheel (also something a 2:20 lap isn't doing) - most occasional DE'ers wouldn't notice this anyway - a driver who is utilizing a LSD will see their times drop as the launch out of corners will be slowed - likely robbing 1-2seconds per 2 minute lap

a street gt3 without a working LSD is able to put down very good times at a track - a working LSD allows a better driver to get those last 2 seconds per 2 minute lap - and when you start running R6s, A6s or slicks the stock unit will fail quickly "if" you are actually activating the clutches - this is the reason the Porsche Motorsport unit is different than the street unit - it actually has to work with sticky tires and last a racing season or two or three

 

i was at VIR 2 weekends ago and needed my rear brake pads replaced. so not having any of my own i had a race shop from S. Carolina( Autometrics) replace my brake pads. so, while they had the car up in the air they saw that my differential needed to be replaced. Cory friedman said the diff's on our cars suck and dont last very long at all. here is a comment he said in a pm to me about replacing the diff...

I would not recommend another OEM differential. The OEM unit wears out quite quickly on the track. The PMNA and Guard differentials are much better suited. Your car most likely does not need the entire differential; I expect a set of motorsports clutch discs will get the job done. We typically get disc packs from PMNA, so I'm not sure if Guard has discs for the OEM diff.

 

+1

I love my RS but Porsche sure pack some garbage in our GT3/RS and sell it as a weekend "track weapon". Porsche need to step up to the plate and fix what's defective and stop hiding behind their racing heritage hoping most consumers are too drunk from the P-car brand to notice they are driving a 1 wheel drive GT3/RS

 

Your Preload is super low that's why the wheel spin freely. Spray one side of the street with water and leave the other side dry. Step on gas hard. If you have skid mark on the wet side then you have a 1 wheel drive GT3 RS ( do this at an area without traffic and alot of rooms just incase your RS go sideway. Don't want to see your new RS get damaged)

 

Oh Boy. Does this mean I should replace the LSD right away on my incoming car? I plan on tracking it as soon as possible after delivery....

 

you dont have to do it right away, but if your pretty aggressive on the track and use hoosiers or stickier tires. your going to need a new lsd after a short while

 

Knowing what I know now, I would if it were my car. Maybe an hour labor and approx $1500 in parts (ramps/clutch disks).

 

See the bold. It's related to my comments below.

The vast majority of why this LSD doesn't work is related to the plates, that's the long and the short answer. As I indicated earlier in this thread, while it's our philosophy to use a moderate to high preload on our LSDs I could build you an LSD that locks just as hard and just as completely with no preload in it. IMHO, preload gets way too much focus in these discussions and what really matters is the friction discs.

rkirshner,
I think there's a certain accuracy to the statement above that Porsche did not just cheap out on this LSD. Though in reality, Porsche may not even have had a hand in the exact design specification of the LSD because it's an item they subcontract out and do not manufacture themselves. The LSDs in these cars are made by GKN, the CV axle company, among other things.

If you rewind to the 993 factory LSD, any of you who have been around a while will remember that they were using carbon plates in those LSDs; dirty filthy nasty carbon plates. Those plates created a perception issue, if not a real issue. Because of that black filth that came out of the gearbox people assumed that having that run through their bearings and synchros and other components that it was doing some damage. Whether that was true or not is debatable. But it prompted a search for a different material to use as a friction disc.

What they came up with is what we see in the cars today. They used a brass material that's very similar to a synchro ring. As such a soft metal the thinking is that any particulate that comes off will be softer than everything else and couldn't really do any damage. And the filthly black mess is resolved. However the tradeoff is that these "new" discs just don't have the same coefficient of friction that the carbon ones did. They just don't bite as much and really need a lot of clamping force (exerted by the ramps pushing outwards on them) to get them to lock. This is part of why the 996 LSD actually works marginally better; the 996 got 40/60 ramps with lower ramp angles, which allowed them to push farther apart and lock harder. The new 28/40 ramp angles are much much steeper and really don't let the cups push apart in the same way and they have really changed the design in such a way that the LSD no longer locks except in a very very extreme condition.

By increasing the preload, what you have done is you've put more force pushing back against the ramps. This is an effective solution to making the LSD work better and I think the reason it's not used more often is that's an awful lot of effort (and if you are paying for labor $$$) to give you something that works ok. And as was mentioned above, it's still going to wear more quickly than something like our discs or Porsche motorsports discs. It's not a bad solution. It's just not what I would consider the best solution.

 

I called Gordon at Autometrics after I saw this post and had a good conversation with him on the subject since he is a customer of ours. What the tech meant in this comment is that they were not sure if we offered an 8 plate clutch pack like Porsche Motorsports offers for rebuilding the LSDs. They were aware of our 4 plate offerings, but they have a certain bias to 8 plate stacks, which they didn't know if we provided. That's their particular bias and it's what they like to use. You can see my bias earlier in the thread. It's a matter of opinion and one of those things that if you ask 5 professionals in the industry you'll probably get 5 different answers on it. But the answer to the question is that I do have 8 plate kits available for anyone who wants them, they are just close to twice the price of a 4 plate kit and unless you're a professional racer with a drive to get on the podium and the pocketbook that it takes to get there (and rebuild your LSD a couple times a season) it's not the route I would suggest for most of you. But if you want it, I got it.

 

Great info. Thanks!!!



-Troy

 

Thanks Matt for clarifying my post. I'm sure we will be in touch very soon

 

Great thread here....my 09 CarreraS came with factory LSD. From reading these posts I am sure it is shot. So for S&G's I took the car to my dealer and told them the LSD is no longer working and to check it out and tell me what they found. Later that day they claim it is working to spec......hummmm...LOL

What I still can not find out is if anyone makes a good replacment clutch pack for my 2009 Carrera S PDK ?????

 

mdrums,
We have not released a service pack yet for the PDK factory LSD. It's being manufactured but we've had some other new product work that's taken priority over it. We'll have it before the end of the year, but hopefully sooner.

 

Matt, may i ask you you a question (s). first , i do not fully understand the "anatomy " of the system. is the fluid in the lsd case the same that is in the transmission? is that the reason that the plates are made of softer material than the gears so that anything that is shed will not impact the gears . are the guard gears also this way ? finally, is the lsd in the 996 gt3 water cooled you have been very helpful to all that have read this thread thanks