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The Cayman factory LSD dissected...

39K views 81 replies 39 participants last post by  the_vetman 
#1 ·
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...
 
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#37 · (Edited)
When I opted for Porsche's factory LSD I was under no illusion that it wasn't track quality. In fact the sales person at the time confirmed this.

The factory LSD is perfect for spirited street driving especially mountain twisties. It's quiet, seamless operation and does an excellent job for traction in conjunction with PSM. I guess if I were to track it I'll wait until warranty ran out & install a more robust LSD.

Having said that I think it's crazy not to opt for the factory LSD if one was thinking of purchasing a MY10 Cayman S for warranty sakes. Like Matt said the factory setup is a good all round solution to safety & comfort & targeted predominantly for the spirited street driver or "weekend special" haha
 
#41 ·
Good suggestions on all counts. Perhaps I should have clarified in my comments that I did not have a stock suspension when I installed my LSD. I do not necessarily believe a LSD will make a Cayman behave badly. It depends on a lot of factors. In my case, it was a combination of the suspension mods I had made plus the track I first ran at with the new LSD. My problems were worse in slow, tight corners, once maximum lateral grip had been reached, and I then tried to apply power. I was not having the same problems at tracks with longer, faster corners.

Matt specifically asked about turn-in. Because I am usually braking heavily at turn-in I wanted to comment about how well the LSD helps the car get settled. It doesn't do that dance from side to side that the stock configuration is prone to. That said, your point about getting the braking done in a straight line and then powering through the turn is well taken. That may be the faster way to get through the corners but it's tough to teach on old dog new tricks! ;)
 
#42 ·
Plates, or friction discs as we call them... This is another thing that's been talked about quite a bit recently. This new Giken LSD out there is being pitched as having more plates (24 IIRC) which offers more locking force because you've got more friction surfaces. All of this is true. It's an equally "correct" way to go about designing an LSD.

As an example I will make another comparison, again using OEM factory parts because we've got a lot of experience with them. The Porsche Cup Cars use an 8 plate LSD in them of a low preload design. It uses that thin little 1.4mm belleville washer that I mentioned above with a very low crown height. That belleville washer introduces very little preload. When those factory LSDs are new, their break test on the bench is roughly 120ft/lbs. That's how much locking they have built into them at rest and it's almost 100% a function of the friction generated by the 8 friction discs.

I build 4 plate GT LSDs with 120ft/lb of preload on them on a regular basis for racecars. To get to that same static locking force, we use a 2.1mm belleville washer. In the field, they will arguably offer close to the same clamping force when the LSD actually locks. But our LSD will offer a more progressive lockup as it transitions. It's got a smoother actuation. Furthermore, as it wears over time it will continue to offer a more consistent "wear pattern" and it's lockup will slowly decrease over time. With the low-preload factory differential it's more of a night and day thing. It will just stop working when it's worn out. There will not be much of a transition there. I sometimes compare it to tires. Some tires have real consistent wear characteristics and you can take them all the way down to the threads before they stop sticking. Other tires you wear them to a certain depth, and even though it appears they still may have more to them, they just get slick and worthless.

Paul Guard obviously spent a lot more years with his ear to the ground listening to the feedback on this stuff than I have. I've only been in this industry for about 8 years, but all that time selling Paul's products. Paul's got a couple of decades experience on me, and obviously was constantly refining his products over time. What he has told me, and I believe him, is that he has not seen any consistent measureable improvement in LSD performance by increasing the number of plates in the differentials. The primary reason that we offer an 8 plate LSD is because Porsche did it. There's a tendency for P-car owners to have a certain OEM is best mentality, so sometimes as a manufacturer in the aftermarket, you make sure you offer something in line with that thinking. It's playing to the "customer is always right" way of thinking.

The practical reality is that I can build you a 4 plate, 6 plate or 8 plate LSD that's going to give you nearly identical performance on the track. Longevity of it will be similar, but we've found that fewer plates wear longer because the more plates we put in the lower we must go on the preload. When we build an 8 plate LSD with our parts, we use generally a 1.0mm belleville washer. It's got more preload and crown height than the factory 1.4mm washer. If I built that same LSD with a 2.0mm belleville washer it would be locked so tight that it would risk breaking the output flanges. I've tried building that LSD just for fun. I couldn't turn it over. There was no "open" phase to it at all. It was well over 200ft/lbs and even with a 6ft long torque wrench I couldn't spin it. That's not an LSD. That's a spool.

I have never built a Cayman LSD with more than 4 plates. I haven't seen the need. I've built a couple for turbo cars with 2.2mm belleville washers in them. The Interseries diffs. are all using 2.0mm bell. washers. Bost of the street cars, that run DEs get built with 1.8 or 1.7mm bell. washers. I could if someone wanted me to. But I don't think there's much, if anything to be gained there. Going from 4 plate to 8 plate adds about $500 to the cost of the LSD and unless the customer is convinced and unwavering that's it's going to make his car faster, I'm not going to make that sale. I won't pitch anyone on that. If they ask for it, I'll talk to them about it and let them make an educated decision on the matter. But you'll never see me put an 8 plate LSD into any of my personal cars. Some of the top PCA racers running 500whp and 600whp 930s and GT2s are running our LSDs as 4 plate units. With that sort of endorsement, I don't know that more plates need even be considered.
 
#43 ·
Matt:

:thanks: very much for taking the time to explain everything.
WHEW! That's a lot of information to process! :eek:
I have to go rest my brain for a while... :hilarious:

Best regards,
Croc'ed
 
#44 ·
You asked for it. :crazy: Most people don't want to know these things that in depth. Most people just want to know that they work and the generalized "how".

And even then I've barely scratched the surface on the black art of tuning the thing. That's something the race teams play with for some time on each new car they run before they get it right. When I ran into Mike from TPC at Sebring back in Feb. he told me it took him more than a year to get it how he wanted it on his personal GT2. We put general "good enough" tunes on these things when we ship them out. It's pros like Mike who can take them to the next level and really dial them in with the rest of the car's set up if someone is really looking to hit the podium with their cars...
 
#47 ·
That's the exact same sort of use my 914 sees. I run a TBD in that car. Any variant of locking differential is better than an open differential. I don't race the 914, even though I take it out to the track some. But I like to drive it in the mountains and country roads around here. And once I finish the engine swap it will have almost three times the power it had stock and I'll need to get that to the ground.

I think that in general the TBD is a fabulous option for the midengine cars. For a lot of us we just don't need any more. They are service free and last forever. They're significantly less expensive than the LSD. They will make the car faster at the track with virtually no compromises on the street. All in all I think they're a great option.

And not to get too far off track here, but I have been getting a lot of questions recently about TBDs for the 5spd gearboxes. Paul never made a TBD for the 5spd. I decided it was time and they are being manufactured right now. I have significantly dropped the production numbers on the 5spd LSDs because not that many people are racing them and don't want to spend that kind of money on a street car. I am replacing that model with TBDs and will put up a special introductory offering in the classifieds when they arrive in my warehouse in the next couple of weeks.

Regards,

Matt
 
#49 ·
Hello,
You guys are very welcome. And thank you. It's nice to be appreciated. I've been pretty put off by some of the anti-vendor sentiment going around some of the other boards recently. I'll need to start coming around more often and participating more actively on this board. You guys seem very technically minded and welcoming.
 
#51 ·
Matt,

You will find our members are quite social, friendly, helpful and technically saavy among other things. We are very proud of our membership here and wouldn't trade them for "other" sites. :) Speaking of which, we vett our sponsors here and don't play favorites as some other sites do, so the quality tends to be higher as well as the participation and sincerity. We aim to please, so please aim! :cheers:
 
#54 ·
No doubt Joel. I also know of a car that's got 80/80 ramps in it. We've got the ability to set these however the customer wants or to make custom ramps to order if a racer wants to play with something. In some instances (not with the Cayman currently) we cut ramps specific to a team's request and don't disclose the configuration or offer it for sale elsewhere. What we provide to the general public is not always what is being run at the professional or near-professional level. Your car is clearly one of those out on that cutting edge with a lot of development time and money spent on making it fast.

You don't know how many GT3 guys think that because they've got adjustable sway bars and skillz that they can have me put a 50/80 ramp in their LSD rebuild and start winning races with no other suspension work other than an alignment. That's really the point of that post. 50/80 or 80/50 is definitely not a "bolt on" configuration and ONLY for racecars. I wouldn't put them in a race on Sunday, drive to work on Monday car.
 
#58 ·
when do you think a TBD or Plate LSD will be available for the PDK cars?
Sounds like not soon.
Having recently seen the PDK LSD from Porsche I do not think
we're going to be making one for that gearbox in the foreseeable future.

I do not consider the PDK in it's current manifestation as a motorsports gearbox!

If the gearbox proves itself and makes it's way into the professional and upper
level amatuer ranks and is being raced, and holds up to that, then I'll reconsider.
 
#60 · (Edited)
Wow - what a phenomenal thread! This grasshopper has learned much here.

I can appreciate this much more from my engineering geek how-do-things-work standpoint than from my driving skills (which aren't that great), but it has given me a lot to think about and I now feel I have a MUCH better understanding of how an LSD works.

It seems to me (though this was really a side-bar to this discussion) if I ever feel the need to upgrade the rear-end of my CS - I fall squarely into the sporting drives on twisty roads, two DE's a year, maybe an AX here and there, not nearly enough driving ability to get any deeper into the track - then a TBD is likely the way for me to go.

Thanks to all for providing such great information!
 
#62 ·
It's our intent to improve the functionality of the factory LSD. We'll definitely offer a standard service pack for rebuilding it to the same locking as it came from the factory. Then we'll also likely do a revised ramp version with more locking for people wanting to race the cars.

Shipping to Australia is no problem. While we never ship complete diffs or gears via US Postal service, for clutch packs there's a Global Priority flat rate box that's very cost effective and efficient.
 
#65 ·
Hello,
I just wanted to update. We're close on this. Probably within the month. Cost is still to be determined, but I expect it to se slightly less than our GT3 kit, which is $750 in parts. Specialist installation is recommended and what they charge in labor will vary from location to location. I bill 1.5 hours ($150) in labor to rebuild them in house from a bare LSD. Removal from the car and ring gear removal are extra costs that should be considered as well, and things we don't generally do.

Regards,

Matt
 
#71 ·
I just had a Guard-prepped GT3 LSD installed in my Boxster and I'm happy with the result. They had a nice 5,000 mile unit that they serviced.

I'd be interested in learning from Matt what typical specs are used when Guard services a GT3 setup. I take it the unit would be a four disc setup. Would it have the 27/22 setup or would it have the 45/65 setup mentioned elsehwere in this post?
 
#73 ·
+1 on the "epic-ness" of this thread! Also the reason I went with GT LSD for my Cayman build. Plus that thing is dang purdy...checked it out at the shop before the install :)
 
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