GTgears

Hello,
We just recently got a Cayman S LSD into the shop and took it apart for the first time. Since this is the first one of these we've seen, I figured I would take some pictures and do a little show and tell with this thing. I think by the time I am finished, the title of this thread will make sense.

Here's the LSD from the outside:

Looks pretty normal for a factory LSD. Cast body, but nothing out of the ordinary. Then we take the cover off:

Here's where it gets a little interesting. Notice that it is in fact a 4 plate LSD, just like a GT3 or any of the other modern Porsche 6MT gearboxes. But, look closely. The friction discs are stacked one on top of the other. Here's the stack as it comes apart:

It goes plain plate, plain plate, friction disc, friction disc, plain plate. So, even though it's got 4 friction discs it's only using 2 of them. Reminds me of another Porsche LSD:

That's a picture of a 1970 911 LSD!!! There's also another similarity between the old LSD and the new one; no belleville washers.

This new Cayman S LSD is a zero preload LSD. In fact there's absolutely no gap inside of this thing. The stack height is pretty much exactly the same dimensions as the body and cap of the LSD. I know there's been much discussion recently about low or no preload LSDs. I'll let you guys debate the merits of those designs, but will ask one question on the subject. If a no/low preload LSD is the way to go, why did Porsche stop using it? And as a follow up to that thought, why now, roughly 25 years later have they gone back to it?

I've got more thoughts and pictures, and will follow up with another post in just a second here...

GTgears

So, the next thing I did was start to look at the internals themselves. They've gone to a new type of friction disc material. I'm not quite sure what it's made out of, but it's a new approach for sure. Maybe they are getting their friction materials from brake technologies. I don't know. If you look at the picture, not only is it some sort of fiber material (reminiscent of the 933 carbon friction discs) but it's "pucked" with the friction material attached with some sort of adhesive:

If you look closely you can see that there's wear on the plates, so it appears that it does bite marginally better than the brass being used in the GT3 LSD:

But what really stood out to me was the size of these parts. They are teeny. Like 904 LSD teeny!


Versus the old 1970 911 LSD (from a car with roughly half the horsepower of a modern Cayman S):


Versus a modern day GT3:


It just doesn't strike me as very much friction surface for locking this thing. But if you look at the ramp angles, they don't really intend this to have all that much lock:

versus the old 40/40 angles of the 911 LSD:


So what's the plan from here? Redesign it so that it works. This came out of an Interseries car that had one season of racing on it. The car owner reported that he was spinning his inside tire for pretty much the second half of the season last year and was effectively running with no LSD. Guys tracking these cars seem to be burning them up really quickly. Our attitude is that there's really no reason anyone who's got one of these units should have to throw it away, so we're going to make parts for it. And having recently gotten our hands on a PDK LSD, it's effectively the same design and same parts, so it will take care of those owners as well.

Please feel free to add your own analysis to what you are seeing and ask any questions that might come up.

Kind Regards,

Matt Monson
Guard Transmission LLC

cello

Is this a "cost of build" issue in your opinion ?? Is there an engineering reason for this design independent of cost ?? You haven't given us your concluding opinion ....

Also, be sure to come back to this thread once you engineer your 'product' or 'build' so we can see your approach and a comparison of the different 'builds' offered.

TIA..

GTgears

cello,
I don't really know why Porsche has taken this approach. From an engineering standpoint it's counter to how we build our products. Porsche has been going with a low preload design now for more than a decade on the GT3 LSDs. And even then, they have barely any preload at all, so this isn't some major change from their other recent designs.

GKN makes these LSDs just like they make the GT3 and Cup Car LSDs. If it was an attempt to solve the friction disc problem seen in the GT3s with the brass discs, I would expect to see the GT3s go to this new disc design and materials as well. But unless they have on the 2010's I haven't seen any 977.2 GT3's using anything but the same old disc design and materials.

As for what our solution will be? We'll give it new ramps that are more aggressive and replace the stock plain plates and friction discs with our own pieces (2 and 2 for a true 4 plate design) using the same materials as used in our own LSDs. And then we'll replace the 3rd plain plate in that stack with a belleville washer. And we can make the discs wider and provide more surface area. There's another 4-5mm on the inside of the discs between the side gear and body of the discs. Not only can the friction surface be made continuous, but it can we widened and still fit within the same space.

Part of the point of this thread is to get the opinions of other members here. There are some serious engineers and techies in our midst on this board. There's guys who know materials and metallurgy and design that will have their own opinions on the how and why of what Porsche is doing here. I'm looking for them to weigh in and share insights on what they think we're seeing here.

ChrisF

Any idea of what your redesign cost might be? Also, does anyone know if Porsche has started selling their LSD's as a part yet?

pedsurg

Matt: Are you also involved in the design and implementation of the gen2 cayman tranny coolers ??

Jack

NJ-GT

Matt,

Thanks for the helpful information. I bet this is the same LSD being used in the 997 Carrera as an option.

That stock LSD wore out rather quickly, half a season of an Interseries Cayman S ? not good at all.

Does your complete GT LSD for the Cayman S Gen I work with the Gen II car? Essentially, can you swap this antique design LSD in the Gen II Cayman S with your full unit available for the Gen I Cayman S?

GTgears

NJ-GT,
There's really been no fundamental design change to the 6spd manual boxes between 2005 and current on the Cayman S. In fact, I have been told that even the non-S 6spd that's going in in the 2010 and 2011 cars is the same, but haven't independently verified that yet. So to answer your question, yes.

The reason I was able to acquire this LSD is because the sanctioning body of the Interseries race has certified our LSD as a suitable replacement for the factory unit. So, many of the racers are ripping out their stock LSD and replacing with ours as they get ramped up for this season. Those cars are 2009 S's.

ChrisF,
I expect the rebuild kit to run $1000-1200. However I have to wait for input from the engineers on it. If you look closely at the picture of the ramps, you'll see that the ends of the factory crossposts are hexagonal in shape. I don't know if that will work with our ramps and angles. If we have to make new crossposts in addition to the other parts,the price will be higher.

pedsurg,
We don't do anything with coolers. That's something that's generally done at the shop level where they are assembling and prepping the cars. We really only manufacture gearbox internals. The "formula" for running a cooler on most gearboxes is pretty similar. Many people tap the drain and the fill plugs with AN fittings, run braided lines out to a Tilton pump, feed it through some remote mounted Setrab cooler and dump it back into the box. The challenge everyone seems to be having with the Cayman gearboxes is that the exhaust from the engine runs right next to it and makes it run hotter than a 911 gearbox. Getting the cooler clear of that ambient heat would be key to getting the gearbox temps down.

Bill Verburg

The older ZF 40% lsd used in 915 also used the 4 plate design stacked as you noted w/ 2 friction and 2 plain plates together ppff. To make it into an 80% the plates were changed to alternate positions pfpf.

GTgears

That's correct, and something people who own these factory LSDs could to do get better locking out of them would be to restack them. However, given the significantly more conservative ramps used in the Caymans they will still be a pretty low lock up. But for a street car that's just tracked on occasion, that may be just the ticket.

On our own LSD we've started making them with the option of lower locking percentages because there are a number of people who feel that the Cayman doesn't need a ton of lock.

JR944

As of this morning, Porsche is not offering the LSD unit separately for the PDK transmission. I didn't ask about the standard transmission. Cost to purchase a replacement PDK box with LSD is over $16k. According to my dealer contact, there is no core credit available by turning in a non-LSD box in exchange.
Joe

GTgears

Hello Joe,

Thanks for that added information. I missed that question on my first read through.

I'll give you a call. I want to talk to you about Dave's core factory LSD. After some thought we're going to offer a core exchange program on factory LSD cores when someone purchases one of our motorsports units. We do it on the GT3s and have no problem selling them off once they are rebuilt. So I see no reason why I shouldn't offer the same service for the Cayman.

The only real shame is that there's only an OEM LSD for the 6spd cars. If someone has a 5spd their only option for that car is to buy one of our aftermarket LSDs. However, in addition to that, we're about two weeks from rolling out our TBD for the Tiptronic gearbox. Then we'll be supporting the whole product line with the exception of the PDK.

KS-CS

For the Cayman/Boxster Tip? For Real!?

Be sure and post it up on Planet-9 when it becomes available - there are several of us there who have been waiting for this for some time.