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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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#2 ·
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
 
#3 ·
Matt,

Great post, thanks for posting this stuff. It's funny you mention this because when I was at the track with Napleton 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???
 
#4 ·
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?
 
#6 ·
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.
 
#7 ·
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??? :hilarious:
 
#8 ·
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. ;)
 
#9 ·
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.
 
#21 ·
Good Morning,
Sorry to leave you guys so long without a reply, but I don't log in much over the weekends.


I don't think it was assembled wrong. This is the same way they did it on the old ZF differentials as well. It doesn't make sense to me either.

When the OEM pieces start breaking down on our new Caymans is Guard likely to have a replacement designed primarily for street use?
When we release our parts they will be based on our current designs and materials except resized to fit within the confines of the factory body. We treat our whole LSD line as motorsports parts, though obviously they get put in street cars on a daily basis. We do take a less aggressive approach on the build when we know it's going to be a street car (see below for another post addressing the set up question). However given the very limited space (short stack height) inside this body I suspect we'll only offer one rebuilding kit. It will be something that you absolutely can track and do DE's with, but if it's a dedicated racecar I think our own models in their entirety will be a better option.

For example, this factory differential uses cast spider and side gears. These are nowhere near as durable or strong as our cnc billet gears. For this repair kit option, we won't be replacing the gears. It would put the cost too close to one of our LSDs. It's not cost effective for you and would result in a product that is too close in spec to our own products. We want to keep entry level products like this entry level.
 
#14 ·
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.
 
#22 ·
Hello Alan,

I think I may have been misunderstood. Having recently seen the PDK LSD from Porsche I do not think we're going to be making on for that gearbox in the foreseeable future. It's significantly smaller than even the Cayman LSD pictured here. I'm pretty sure the discs inside of it are the same and our parts will be able to interchange with the stock parts, but it's got even fewer plates inside.

But there is a deeper issue at play here. Hold on, here's where I speak blasphemy in some people's eyes: I do not consider the PDK in it's current manifestation as a motorsports gearbox! I know it shifts faster. I know lap times are better. But can this thing stay together for a whole season of PCA 1 hour enduro races? What about a season in the Continental Tire series with multi-hour long events. What about a 12 Hours of Sebring or 24 Hours of Lemans? I'm going to wait and see. I'm not convinced. When Porsche used the PDK in the 962 it was for endurance racing with professional factory drivers who knew how to keep a car together for an endurance event. To my knowledge they never put the gearbox in a sprint event. If the gearbox prooves 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.

But for now my relatively limited R&D dollars and inventory commitment is going to things that are more of a sure thing. Right now that's gears and mainshafts for the 6spd Cayman gearbox. That is being raced and is breaking. We'll support that with product because it's prooving to be a viable market. The PDK, from my perspective is more a part of that whole Grand Touring movement I described above. I think it's a fabulous gearbox for a street car. It lets us feel like a formula 1 racer and gives Porsche something to draw people away from the Mercedes, BMWs, and Nissans that are directly competing with the Cayman as retail. But I don't think it's got the durability to win races. It's a pseudo-sequential gearbox. To race at the top level, a real sequential gearbox will be what's required.
 
#19 ·
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
 
#24 ·
So now we're getting a bit into this idea of tuning the LSD that was asked about. I'll be up front and tell you that the Cayman is a bit of an anomoly here and is something that we're still learning about. There's different opinions on how to properly set up an LSD for the Cayman's mid-engine application and I'm going to refrain from expressing a strong opinion on the matter.

Historically, with the 911, if someone has a street car or what I call a "weekend special" we go with a 40/60 locking percentage. With that, the 40% is the acceleration, and you want it that "loose" because it keeps the car nimble. With that low of a percentage, you can have a lot of difference from side to side between the two wheels before the LSD kicks in and locks. This lets the car turn well on corner exit. But it's not terribly aggressive, which means if you are in a tight 2nd gear turn, or in your residential neighborhood trying to flip a u-turn after picking your kid up from school, it's not going to lock on you. But it's a compromise under racing conditions. If you're burying the throttle in 3rd gear coming out of a turn and your inside tire starts to spin, you want it to lock quicker. The sooner it locks, the sooner the wheelspin stops and the sooner you get power to the ground and are accelerating again.

On the braking side of it, what the lock up does is provide rear end stability. And here's part of where the controversy comes in. Historically (like back to the 914) many Porsche racers have felt that the mid-engine cars do not need as much deceleration lock up as the tail heavy 911 has required. As such, the LSD have been set up like you would set up a front engine, rear wheel drive vehicle. So instead of the above orientation of 40/60 they are reversed and set up the other way around. On the Cayman that would be 65/45 (the first batch of Cayman LSDs out there were 60/40. For the last couple of years they've all been 65/45). This is the same way you would set up something like an M3 or a Miata. On a racing 911, you run an 80% lockup to keep that back end in line. With the Cayman that arguably isn't required. And furthermore, because of the midengine configuration, you can run higher locking percentages on acceleration without it exhibiting major changes in to how the car handles. If you go much beyond 50% locking on a 911 it wants to throttle steer and slide the rear end. With mid-engine you can go higher than that.

So here's where the controversy lies. There's a number of people out there who feel that you should set up the Cayman LSD like a 911 with a high locking percentage on braking. There is also a group of people out there running torque biasing differentials (which ONLY have lockup on acceleration) who feel that they offer a faster configuration. And then there are the "traditionalists" who feel you should set the Cayman LSD like people have historically done the 914's with high lock up on acceleration and less on decel. While people come to us as the experts on this, I'm not the kind of guy to fake it. What I mean is I have been asking people who are racing these cars and playing with these differentials to continue to give me feedback based on their personal experiences. With the Interseries cars, they mandated that we set the LSDs we're selling for that application at the "traditional" setting of 65/45. Every one that leaves this facility has been set that way, and everyone running those cars does have the same set up. However there are other racers playing with the set up on them and giving me input. At this point, if it's not for an Interseries application, I take the "customer is right" approach and stack it how they want it. Some guys want it 65/45 and some guys want it 45/65. But most of the ones in the field and in the cars of people reading this are set at 65/45.

What about 80/50? Well, we went away from that setting pretty quickly on the Caymans and Boxsters. When set at 80% locking on acceleration the cars got too tail happy on corner exit. The people that were running them didn't like it. Would 50/80 be a good set up for a racecar? Only time will tell. There's a couple of guys running that set up right now and I'll post feedback as it's provided to me. But what I do know is that I wouldn't go 50/80 (or 80/50) on one of these cars without coilovers and adjustable sways. LSDs that aggressive do significantly change the handling of the vehicle and you need the ability to dial out oversteer or understeer as needed with the introduction of the LSD. I strongly discourage our 911 customers from going 50/80 without that ability and the same would hold true for a Cayman.
 
#53 ·
What about 80/50? Well, we went away from that setting pretty quickly on the Caymans and Boxsters. When set at 80% locking on acceleration the cars got too tail happy on corner exit. The people that were running them didn't like it. Would 50/80 be a good set up for a racecar? Only time will tell. There's a couple of guys running that set up right now and I'll post feedback as it's provided to me. But what I do know is that I wouldn't go 50/80 (or 80/50) on one of these cars without coilovers and adjustable sways. LSDs that aggressive do significantly change the handling of the vehicle and you need the ability to dial out oversteer or understeer as needed with the introduction of the LSD. I strongly discourage our 911 customers from going 50/80 without that ability and the same would hold true for a Cayman.
Just as a counterpoint here, I installed one of the first Guard LSD's in my Cayman (now sold to cgomez). It had the 80/50 lockup. Car is full race with 900/1000# springs, stiff sways, motons, hoosiers, etc. The 80/50 works perfectly with this race setup and my driving style. I can understand how a traditional 911 driver may not like the setup, but for me it was perfect. I only bring this up to say not to dismiss the setup for all potential customers!

(Note the car has PCA class records at at least 6 major tracks across the country now, so it is fast to boot!)
 
#25 ·
First of all, Matt, thank you for taking the time to provide us all with such a detailed understanding of the oem LSD in the new Caymans, as well as your thinking about the setup in your own diff's. This information is extremely helpful to those of us trying to make decisions about how we would like to try to improve our car's performance. Between all the text and the photos we know how much effort you have put into this post. I, for one, am very grateful for this.

I own one of your 65/45 LSD's. It has been in my '06 CS for a year and a half. I am a very happy customer of yours! I am now in the process of trading my '06 for a new '11 CS. I will be removing my Guard LSD, and all other mods, prior to trading the car. I've been trying to decide whether or not to order the new car with the factory LSD. My long range goal is to buy a used CS and convert it to a track-only car. I was thinking about holding on to your diff to install it in that car. Based on your assessment of the factory unit I think I will pass on the oem unit and put the Guard one in my new car.

From my own personal experience, I would definitely agree with Matt's comments that a more aggressive LSD, like the Guard unit, can definitely affect ther handling of your car. In my case, the difference was profound. As Matt suggested, I needed to purchase adjustable sway bars so I could tweak the balance and sort it all out. The end result was a large improvement in handling.
 
#28 ·
Matt:

It is good to see you active on the boards and thank you for detailed, unbiased information.

One thing I haven't heard as feedback thus far, which I assume is a good sign, is the heat build up with the 60/40 or 65/45 setup. Have you heard of any issues on this, and wether you recommend a different trans oil? I used to use Redline with your GT LSDs on Bimmers, which was quite nice, but don't want to make assumptions.

Thanks again,
 
#29 · (Edited)
Matt:

Thank you very much for your thorough reply. IMHO, educational posts such as these are what makes this website priceless. I/we now have a much better understanding of how a LSD operates. If you don't mind, I'd like to pose a few more questions:

The factory LSD appears to have much steeper ramp angles (by my eyeball, approximately 75 degrees) than the GT LSD, plus both ramps appear to be symmetrical. Does that make the factory LSD "looser," thereby allowing greater wheel spin before locking?

Does the Boxster/Cayman's differential turn in the "reverse" direction from a 911's? If so, would the same 65/45 LSD installed in a Boxster/Cayman
function as a 45/65 LSD when installed in a 911?

Please clarify your earlier comment about using a Belleville washer (or the factory's lack of one?) Is this washer used primarily to compensate for clutch wear, or does it perform some other function (or both?)

Also, please comment on the quantity and stack-up of plates and clutches as they relate to street, dual-purpose (aka "weekend warrior") and race car tuning.

FWIW, and I don't mean to start a war here, every time I've mentioned to a more seasoned driver (PCA chief DE instructor, PCA club racer, and professional GT racer) that I was thinking of installing (or had installed) a LSD in my car, they have advised and/or commented positively on my selecting a plate/clutch style LSD, and especially so on your company's products. I'm sure there are other quality options on the market, and to each his own, but I for one am a satisfied customer of yours.

Regards,
Croc'ed
 
#40 ·
Good Morning,
First off I want to thank Jonathon for posting a link to that "old" thread. I just finished reading it and it's the most in depth discussion I have seen on the web regarding Cayman chassis dynamics and set up when involving a new differential. It's good to see that the members here get it. I find myself constantly telling people that an LSD or TBD is not some magic go faster pill. On certain chassis with stock suspension it doesn't upset anything. But absolutely if one is building a car for racing and lap times it needs to be approached as a system and so many times people do not incorporate the drivetrain and differential into their "suspension" tuning. It's probably close to once a day that I tell a GT3 or TT owner that they don't want to go 50/80 on their daily driven, sometimes tracked car with next to no adjustability. So many people just don't get that when you go to a bigger sharper knife you need to have the accomanying other things to use it properly so you don't cut yourself. Like many things in motorsports the closer you get to the performance limit, the more twitchy and consequential things become. Now on to the questions.
The factory LSD appears to have much steeper ramp angles (by my eyeball, approximately 75 degrees) than the GT LSD, plus both ramps appear to be symmetrical. Does that make the factory LSD "looser," thereby allowing greater wheel spin before locking?

Does the Boxster/Cayman's differential turn in the "reverse" direction from a 911's? If so, would the same 65/45 LSD installed in a Boxster/Cayman
function as a 45/65 LSD when installed in a 911?

Please clarify your earlier comment about using a Belleville washer (or the factory's lack of one?) Is this washer used primarily to compensate for clutch wear, or does it perform some other function (or both?)

Also, please comment on the quantity and stack-up of plates and clutches as they relate to street, dual-purpose (aka "weekend warrior") and race car tuning.

Regards,
Croc'ed
The factory LSD does have significantly steeper ramp angles. IIRC, they rate that LSD at 22/27. It's a very "soft" locking percentage. This is probably why the guys who do take cars to the track on stock suspension with the OEM LSD don't have the same problems Jonathon did needing to change his set up. As was discussed in that thread, the low locking rate doesn't allow there to be enough power to the ground to overpower the available traction and make the car loose.

Regarding 65/45 versus 45/65, the ramps are symmetrical and swappable within the differential bodies. We can set it either way. Both the 911 and the Cayman/Boxster run with the ring gear on the left side of the car, and they do spin the opposite direction of each other. The 911 rotates the ring gear CCW, whereas the midengine cars rotate is CW. So, to answer your question, if you were install the LSD from a G96.00 into a G86.20 it would go from 40/60 to 60/40(I made that example because those are the only two gearboxes from the 911 and Boxster/Cayman line that share parts so it's actually a possible thing to do).

Belleville washers... Belleville washers are a complicated thing. They are the source of the preload on the differential, which these days seems to be a controversial topic. There seems to be a movement towards low or no preload differentials. We use belleville washers and a high to moderate preload and intend to for the foreseeable future. The preload generated by the belleville washers has a direct effect on the locking force the differential is able to generate. For our differentials we make, on average half a dozen different thicknesses of belleville washers and this is our primary tool for tuning the performance of the differential aside from that actual ramp angles themselves.

Keep in mind, that a belleville washer is functionally a spring. When it's compressed inside of the differential it's "loaded" and has a certain tension. The thicker the belleville the higher that tension is. It's pushes back against stack and introduces the preload, which in effect increases the overall amount of ft/lb of clamping force the differential can generate within the clutch stack.

So, I'll make a somewhat arbitrary example using the 911, because it's an easier place to pick one from. Say Jon drives a 1976 911 with a 160bhp 2.7l engine. His brother James drives a 1976 930 that's been tweaked and his 3.0l puts out 400bhp. For the same application (let's say road racing) James requires a differential that offers more than twice the locking force when it's locked for the LSD to do it's job. Even if we were stacking both LSDs to 50/80 we'd put thicker (more powerful) belleville washers into James' LSD.But there's tradeoffs there. The higher the preload, the more off and on the LSD tends to be. If we use a 1.7mm bell. versus a 2.1mm bell. the transition on locking tends to be smoother and less dramatic. So there's this balancing act of putting in the lightest belleville washer you can that will still give you the maximum locking force so the LSD can do it's job properly. This is one of the things that pro-racers play with throughout the season as they use our diffs. Many shops buy an assortment of washers and experiment with them during testing days to find the preload what makes the diff. work the way they like it best for their particular car.

One advantage of the bell. washers, that you mentioned, is they do play a role in the durability of our LSDs. Some people have argued that high preload on our motorsports LSDs makes them wear out quickly because the plates are constantly grinding against each other. In practice we just haven't found this to be the case. On average, for a PCA Club racer in a dedicated track car, low power and high power cars alike tend to get anywhere from 3-5 seasons between services. Instead of causing premature wear, because they raise the locking force, and because they have a nice high crown height, they keep the differential tight and help it to continue locking over a greater period of time with more wear allowed on the parts before they are out of spec.

Again, going back to the 911 example, with the GT3 this time, I'll compare the factory LSD in that car. That car uses a 1.1mm bell. washer with a 2mm crown height. For comparison our "softest" bell. for that car is a 1.8mm washer with just shy of a 5mm uncompressed crown height. That taller more powerful washer,applies more force to the stack. While we do believe the friction discs used in the OEM GT3 LSDs leave a lot to be desired, we've found that just the addition of 1.4mm Cup Car belleville washers (or our 1.8mm with some thinner plain plates to account for a proper overall stack height) will substantially increase the lifespan of that differential. If Porsche would just put more preload in that differential from the factory you would see practically no complaints from people because they are "wearing them out" prematurely. The practical reality is that just like this Cayman LSD I tore apart, the GT3 LSDs show next to no wear on them when they are reported to be failing. They get as little as .1mm of wear off the friction surfaces and they stop having enough friction to lock. With more preload on them, they keep locking for longer.

I'll continue with plates in the next post.
 
#31 ·
Hello FT,

The Cayman gearbox has heat issues. It's not any direct result of adding an LSD. I'm hearing of them running hot from pretty much everyone that's racing them, whether they are using our LSD, a factory one, or some variant of a TBD (both Quaife and us make one). A big part of the problem is the adjacency of the exhaust. And it doesn't help that there's no steel synchro option for the box. Steel synchros would be a big upgrade for a racing application because they hold up better in a hot gearbox than brass or carbon ones. And an external cooler away from the heat of the engine and the exhaust would be a major improvement.

As for gear oil? I wouldn't use Redline in it. In my experience I feel that at racing temperatures the Redline oils (even their NS variant) get too slick for the brass synchros. In something like a BMW with an independent rear end, Redline is a good choice. It's actually what we run in my wife's Subaru's rear end. I know of a few Cup Car racers who run it and love it, but again those are gearboxes without brass synchros, as they either have steel motorsports synchros or are dog box sequential gearboxes with no synchros at all.

What we recommend for gearboxes with heat issues is Lubrication Engineers. It's a little harder to get than the more popular Mobil One Delvac or Shell transaxle oils. But during testings, a few years back when Paul Guard still owned the business, they saw greater than 20 degrees in temperature drop in the gearbox when they changed to this oil. On a box that's already got heat issues in it from the factory, that kind of temperature drop is huge. I don't generally aggressively recommend any one oil to the 911 guys. But with the Cayman and Boxster gearboxes I think it's more important because they do run hot.
 
#36 ·
The Cayman gearbox has heat issues. It's not any direct result of adding an LSD. I'm hearing of them running hot from pretty much everyone that's racing them, whether they are using our LSD, a factory one, or some variant of a TBD (both Quaife and us make one). A big part of the problem is the adjacency of the exhaust.
When I had the stock exhaust I did notice the car ran stinking hot. It is a LOT cooler now with the change to a Capristo exhaust.
 
#32 ·
Is heating also an issue with the PDK?
 
#34 ·
I dunno. Find me someone who has run one for a couple hour long event. I don't know anyone who is racing the thing seriously. I haven't even talked to anyone who is running one in PCA enduro length Club races. It would be a good question to post up on the various Porsche forums and see what people have to say about it. It's not a topic I can offer any firsthand or secondhand input on.

Croc'ed,
I'll answer your further questions in the morning. You posted that just as I was replying to FT and I didn't see it until just now. My wife is on me to shut down the computer and spend a little time on the couch with her before bed. But I can't complain...Top Gear is on BBCA.
 
#33 ·
Matt, you really confirmed my fear, which I was trying to have a positive outlook. :) However, as you said, I do not think, not that I really know first hand, if any LSD would make it worse, maybe clutch packs would.

I did not know about LE oils, thank you for the recommendation, I'll give it a try once I have your LSD.

Thank you once again.
 
#35 · (Edited)
The difference in my car's handling after installing the Guard LSD was profound. I posted about this back then and we got into a long, heated discussion about LSD's in these cars. There were many thoughtful comments made in that post. Anyone giving serious thought to purchasing a Guard unit, or thinking that the oem unit is a viable option for track use, would be well-advised to check it out.

http://www.planet-9.com/cayman-boxster-modifications/26730-limited-slip-dif.html

In short, the most notable difference was the uncontrollable power oversteer caused by the LSD. I was only able to get the car back into balance by installing the adjustable sway bars. The car needed to be a lot stiffer in front in order to keep the rear planted.

As my driving style is to use a lot of trail braking, the LSD made an appreciable difference in turn-in because the rear end of the car feels much more planted and stable under heavy braking.

Just to be clear, a good-quality LSD, like the Guard unit, is definitely a meaningful upgrade in the performance of our cars on the track. They are really not necessary for street use. And just to confirm one other point Matt made, it's already pretty clear that a diff cooler is needed for serious track/racing use.

I have been using the Lubrication Engineering gear oil since my diff was new. It ain't cheap but it's good stuff!
 
#39 ·
jonathan,

I'm not an instructor. I currently run in the black group in PCA DE events, and I too have installed the GT Club LSD in my Cayman. The only suspension changes I've made to my 2.7/non-PASM Cayman are GT3 LCAs in front, and an alignment set to -1.5F/-2.0 R camber with zero toe, while running NT-01s. I have not experienced any "uncontrollable power oversteer." On the contrary, I find it very controllable, and utilize this "instability" to rotate the back end of the car in tight turns. This helps to both tame our cars' inherent understeer, and preserve the outside shoulders of the front tires.

I suggest that you may want to adjust your "trail braking" driving style to take better advantage of the LSD. Specifically, by getting off the brakes and rolling onto the throttle earlier in the turn (i.e. brake, turn and go!). What you're describing makes me suspect that the LSD is locking up somewhere in the middle of the turn, upsetting the rear end grip just when you need it most. On those turns where trail braking is appropriate, then smooth inputs in both steering and brake-to-throttle transitions are critical.

I'm sure that the other suspension tuning you've described are valid to best tune the chassis to complement the LSD, and have been sorted out by better/more experienced drivers than me. But it also helps to learn different driving techniques, to be able to adapt your driving style to the situation at hand.

Best wishes on your quest for a beautiful new street car, and a track toy, too! You're a lucky man to have both.

Best regards,
Croc'ed

The difference in my car's handling after installing the Guard LSD was profound...

In short, the most notable difference was the uncontrollable power oversteer caused by the LSD. I was only able to get the car back into balance by installing the adjustable sway bars. The car needed to be a lot stiffer in front in order to keep the rear planted.

As my driving style is to use a lot of trail braking, the LSD made an appreciable difference in turn-in because the rear end of the car feels much more planted and stable under heavy braking.
 
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