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Thread: The Cayman factory LSD dissected...

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    The Cayman factory LSD dissected...

    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.
    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...
    Matt Monson
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    Re: The Cayman factory LSD dissected...

    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. You could restack them with the friction discs further split apart for more lock up but the ramps are still really gentle. I don't think as it stands it would be much better for a racing application, but may be just fine for a street car. Regardless the wear surfaces are really thin to start with and there's just not ever going to be a really long life out of these LSDs.

    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 at the same time improve 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
    Matt Monson
    303-530-1094
    gtgears@yahoo.com

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    Re: The Cayman factory LSD dissected...

    Matt,

    Great post, thanks for posting this stuff. It's funny you mention this because when I was at the track with napletonicon we had a couple of different Caymans acting differently with their LSDs and indeed one that felt like it didn't have an LSD at all that my TBD was outperforming by a long shot. So why are these Porsche LSD's like this???

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    Re: The Cayman factory LSD dissected...

    Quote Originally Posted by Guard Transmission View Post
    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...
    Couldn't you just switch a plain plate and friction disc and all four friction discs would in use?

    So it would be plain plate, friction disc, plain plate, friction disc, plain plate.

    Porsche only claims 22%/27% lock up so would using all four friction discs double that number?
    And then improving the ramp angles might make it a decent diff?

    Is there room to build an LSD with larger diameter discs and plates?

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    Re: The Cayman factory LSD dissected...

    Quote Originally Posted by K-Man S View Post
    Matt,

    Great post, thanks for posting this stuff. It's funny you mention this because when I was at the track with napletonicon we had a couple of different Caymans acting differently with their LSDs and indeed one that felt like it didn't have an LSD at all that my TBD was outperforming by a long shot. So why are these Porsche LSD's like this???
    My guess is cost/noise and the fact that real deal diffs likely need rebuilt.

    That is why we put motorsport or guard diffs in modern porsches
    Casey Parkin : Washington, DC

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    Re: The Cayman factory LSD dissected...

    K-man,

    I think part of what we are seeing here is Porsche's continued push away from really high performance automobiles and more towards GT cars that are safe and comfortable, that still perform well, but not stellar. I don't think when they put together the specification on this LSD that they ever intended it to see the track. There's a number of street drivers who are perfectly satisfied with the performance of this differential, especially when you leave all the various electronic traction control items engaged. It's being developed as an integrated system and the practical reality is the LSD isn't expected to do as much as it once did because the brakes are automatically more involved than they were in the past.

    But then you take the car to the track. And you turn off the electric babysitters so that you can really feel the car and drive it at the limit without the computers stepping in and saving your arse when you push it too far. It's just too much for this little LSD. Or in some instance they get in your way because you and the car can go closer to the edge than they will let you and they step in and pull you back, making you slower but safer. Heck, it's too much for the street GT3 LSDs which are having a catastrophical failure rate when taken to the track. Even Porsche's flagship trackday special is ill equipped for use on the track in this department. And if the new TT model (only offered with a PDK and electronic differential) is any indication they are just going to go further to the side of electronics in the road cars going forward. Technology is a double edged sword here. The cars keep getting safer and more comfortable, but at the same time we keep getting further removed from them and the real control of the driving experience. Just look at how they are advertising the newest GT3R. They are openly calling it a racecar that's easier to drive for a gentleman racer that doesn't need the skills of professional.

    Porsche has been systematically making their LSDs less aggressive on all their cars for a while now. IIRC, the current GT3 is 28/40 locking versus the 40/60 they used on the 996 variant. The GT2s have used the lower locking percentages since the 996 version of that car. It stands to reason that they would go low on the Cayman as well. It makes the cars more forgiving and basically makes it harder for the street driver to catastrophically fail and do something really stupid that kills or maims people because they pushed it too far. But for the people racing and tracking the cars, it disables them. This is why there will always be a healthy aftermarket for Porsches, because people will always want to race them no matter what Porsche does with the product line.

    Walter,
    If you read the end of my second post, you will see that I did suggest that you could restack them in the traditional configuration. But given how the ramps are set up, I don't think it will actually double the locking percentages like it did on the old 911/915/930 ZF LSDs. You can see what those ramps look like compared to the Cayman ones. This is just a guess, but I would say that restacking it might get you to something like 32/40 but not much more.

    Other than the ramps, there is the very small area of the friction surfaces. And beyond that, they are so dang thin I don't see them having a very long service life. Those friction discs have a total thickness of 1.6mm. The pads are .3mm each. And since it's got no preload and very limited ramp movement I just don't see them being able to take more than .1mm of total wear on them before they stop locking. The GT3 LSDs, which have low preload are failing in about .1mm of wear. For comparison, our LSDs will continue to lock with up to .4 or .5mm of wear on them. In practice what we see is our diffferentials will go 3-4 seasons of PCA club racing between rebuilds, compared to GT3, and now Cayman S, LSDs that last less than one whole season. So, in short, I don't think restacking them is a solution that will work for very long in a racing environment.
    CBRacerX likes this.
    Matt Monson
    303-530-1094
    gtgears@yahoo.com

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    Re: The Cayman factory LSD dissected...

    But Matt wait wait wait, just look what Porsche has to say about it:

    Porsche Technology Glossary

    "Are you a fan of sporty driving? In your spare time, do you enjoy the occasional outing on the racetrack? Then you shouldn’t do without the new optional mechanically locking rear differential available in conjunction with 18-inch or 19-inch wheels."

    "In other words, sheer driving pleasure and faster lap times."

    They say its great for the track, how can they be wrong???

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    Re: The Cayman factory LSD dissected...

    OK,
    Now that's really funny.

    I didn't mention it, but this LSD is made by GKN, just like the GT3 LSD is. While the issues with the GT3 differentials have been going on here in the states now for half a dozen years, Porsche doesn't really acknowledge an issue with them and warranty coverage of the failures is intermittent at best. I suspect it will be the same with the Caymans. Just last week I rebuilt a GT3 LSD for a customer because his dealer had denied his warranty claim and accused him of tracking the car and causing the failure through abuse. Clearly PCNA and PAG don't see eye to eye on how these cars are meant to be used.
    Matt Monson
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    Re: The Cayman factory LSD dissected...

    Nice tear-down.

    I got the factory LSD in my '10 CS 6-speed, so I will definitely be interested in hearing what kind of "upgraded" rebuild you might offer, if this thing is going to fail that quickly. That's kind of disappointing, since the addition of the factory LSD was one of the things that caused me to buy a new car rather than something slightly used.

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    Re: The Cayman factory LSD dissected...

    Part of me is happy that I skipped the factory LSD for my 2010 CS.

    I really won't be too happy to rebuild it from time to time.

    Plus I don't think I need LSD for the street, I barely track the car anyway.
    2010 Porsche Cayman S PDK

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    Re: The Cayman factory LSD dissected...

    Great information and pictures, thank you for taking the time to post this..!

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    Re: The Cayman factory LSD dissected...

    Thanks for sharing - this is all very good to know. I will be interested to see what you come up with. Stacking friction discs against each other just doesn't make any sense to me. Could it have been assembled wrong?

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    Re: The Cayman factory LSD dissected...

    When the OEM pieces start breaking down on our new Caymans is Guard likely to have a replacement designed primarily for street use?
    Croctor

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    Re: The Cayman factory LSD dissected...

    Matt,

    Glad to hear that a GT diff will be available for the PDK users. I had 3 transmissions built by Brian Copan and he used your gears in all 3. The best one also had your diff. I received a good education from Brian on the 'quality' factory diffs.

    Please let me know when a Guard diff will be available.
    Alan C.
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    Re: The Cayman factory LSD dissected...

    Quote Originally Posted by DrKareem View Post
    Part of me is happy that I skipped the factory LSD for my 2010 CS.

    I really won't be too happy to rebuild it from time to time.

    Plus I don't think I need LSD for the street, I barely track the car anyway.
    Doc!!! From what I know about you, I think you & I track our cars every time we drive them on the streets!
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    Re: The Cayman factory LSD dissected...

    Quote Originally Posted by HassaanAbdeen View Post
    Doc!!! From what I know about you, I think you & I track our cars every time we drive them on the streets!
    true
    2010 Porsche Cayman S PDK

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    Re: The Cayman factory LSD dissected...

    Quote Originally Posted by DrKareem View Post
    true
    I doubt the OEM LSD could handle your driving!
    Croctor

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    Re: The Cayman factory LSD dissected...

    Great info! Thanks for sharing it. One of the reasons (among others) that I ordered an '08 instead of waiting was that I knew if I wanted an LSD that you guys made a great one. Now you're making my decision look like a good one.

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    Re: The Cayman factory LSD dissected...

    Matt:

    Perhaps you can show a few photos of one of your products disassembled, side-by-side with the factory unit for comparison purposes, with a brief explanation of the different features (e.g. ramp angles, clutch packs, preload, etc.) and their benefits. Maybe the "987 Club" model that I've installed:

    Limted Slip Differential - 987 Club - Articles

    Also, I think many of us would find it helpful if you would describe briefly how you'd "tune" a LSD for different applications (e.g. street, autocross, DE, racing.)

    Regards,
    Croc'ed

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    Re: The Cayman factory LSD dissected...

    Quote Originally Posted by Croc'ed View Post
    Matt:

    Perhaps you can show a few photos of one of your products disassembled, side-by-side with the factory unit for comparison purposes
    Also, I think many of us would find it helpful if you would describe briefly how you'd "tune" a LSD for different applications (e.g. street, autocross, DE, racing.)
    Regards,
    Croc'ed
    Oh yes that would be great, please...?
    .

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