996.1 limited slip differential (LSD) on a 996.2? Why (not)?

EDIT : While there are a lot of informative posts in this thread thus far, my original post is, well, not the best example. This was all about "why is there a 996.1 LSD on my 996.2, and will it work?" But as of page two of this thread, it emerged that the guys working on my car seem to have gotten it rather wrong. Because it seems the 996.1 limited slip diff on my 996.2 is, strangely enough, a 996.2 open diff (though apparently manufactured after my car was and using 996.1 LSD mounting hardware, so there is still at least a bit of a puzzle ... ) In order to install a new limited slip differential, we put the car on a lift and found … a limited slip differential. Interesting. It’s not on the option stickers or the spec sheet. Also, it seems to be the differential from the 3.4 liter cars that seems to have been discontinued in ’99 (if I understand the PET correctly). More interesting. The 996.2 was not available with that or any other limited slip differential for the first few years of production, and I thought this was because Porsche had no differential that worked with PSM. I discussed this with my local specialist who was quick to conclude that with PSM on, the electronics engage before the diff can, so it makes no difference unless PSM is off. But it would be strange if Porsche didn’t offer an LSD in 2002 for this reason alone. And I’d think this would still be true of the LSD they finally introduced for the 996.2 later on (2004?). It seemed to work fine on my car (though now I understand the chuntering noise in parking garages), but who knows, maybe PSM was never really working (properly) all this time, or maybe the diff is worn out and behaves like an open diff. Or maybe had I known I had a limited slip differential and rushed out to go drifting the few times there was enough snow, I’d have found there was a reason the car was never offered with this LSD … . I won’t be installing the new LSD soon – finding the Porsche LSD also meant finding incompatible mounting hardware – so the old Porsche LSD goes back. But unless it snows, and with no track time coming soon, I won’t really know what it’s doing. So if anyone knows what this diff will/won’t do in a 996.2, I’d love to hear it!

The 40th ae car has a limited slip diff and PSM And I have put a guard transmission modified 40 ae diff (40/60) in my 2004 c2 with PSM . It works fantastically even with the PSM on ,PSM allows 8% slip so the lsd engages before the PSM in most situations ( ie accelerating hard out of corners) I highly reccomend uprating it with the guard bits , the stock porsche internals wear very quickly . the car doesn't bog down off the line when you floor it like it did with just the PSM , the car just grips and goes .

Good lsd info https://rennlist.com/forums/996-gt2-...ntial-lsd.html

Good lsd info https://rennlist.com/forums/996-gt2-...ntial-lsd.html Guard rebuild https://rennlist.com/forums/gt2-and-...d-install.html

The reason Porsche did not fit LSD from the factory to PSM equipped cars * was two fold. The e-LSD function -which is a subset of the PSM system- relied on the ABS system (i.e.: pulsing the brake pressure of the spinning wheel under power), as well as the ability to unload a driven wheel -or apply power to it independently of the other wheel on the same axle- would a- be damaging to the LSD b- interfere with the stability functionality. * LSD was a very rare 2005+ 996 Turb option which had modified PSM programming, as with the anniversary cars also equipped with modified PSM programming and a very low lock up rate LSD to facilitate PSM functionality. Further, the MK2 cars have a significantly stronger transmission. I’m not sure you’d want to put an MK1 diff in an MK2 transmission, if it fits. I prefer drifting a car with a mechanical type LSD, FAR easier to control, a lot more predictable and communicative. That said, you can drift an open diff Carrera without too much effort, especially on loose surfaces.

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Thanks for this and the links! To avoid any confusion, I know the 996.2 works with the later diff, as well as with the Guard upgraded later diff. What I'm trying to figure out is if it works with the earlier diff from the 996.1, in particular the one where it says in the PET "-99", in other words, available on model year '99 cars and earlier. (I'll try to upload a part number.)

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Are you sure about the 40ae having different PSM programming? That diff was an option for other 996.2s, as well as a retrofit for earlier 996.2s, and I never heard that they came with/required different PSM (re)programming. It fits. Not sure what it does/does not do when it's there. But it fits. For example?

Other than changes in the ramps for different locking percentages they are the same units. You can mix and match 996 and GT3 lsds in any year of these cars. Ps. An early 996 gearbox will have a little casting rib inside the case that needs to be dremelled off. On later gearboxes they did it to all of them at the factory. You will also need bolt in axle flanges, but you need that on a 996.2 as well.

rs10 , I’m not sure what you’re asking when you say which cars I prefer drifting with an LSD. I loved drifting my GT3 - coincidentally it had an upgraded diff from GTgears - though my first 99 Carrera with an LSD was fine, as are any other cars with a clutch type LSD like an e36 M3 or whatever. Suspension has a lot to do with this as well but a proper LSD is good for more than just drifting. Anyway, here’s a video of my shenanigans in that 996 GT3 if you care to see. Drifting VIR with a Porsche GT3 - YouTube ANYWAY, to the best of my recollection here’s the comprehensive list of LSD equipped 996s from the factory (not an option after 1999, either standard or not available depending on the model): *Optional on the Carrera 2wd until end of production for 1999, not in conjunction with e-throttle or PSM, not available after e-thorttle became standard in 2000 with the following exceptions: *40AE - low lock up rate LSD standard in conjunction with different PSM programming *Turbo very late model option - low lock up rate LSD from the factory in conjunction with different PSM programming *GT2/GT3- No PSM, standard LSD To be clear, I’m not saying you can’t install one, or that it wouldn’t work into an e-throttle equipped car, but rather the reasons for why it was not done from the factory. If I were doing this over, and wanted to install an LSD into a car that didn’t have one from the factory, I’d either disable PSM entirely - or start with a car that didn’t have it to begin with. GTgears may have more info on this as they supply proven aftermarket LSD solutions for many Porsches. (If they’re the same people as Guard, I believe they are). Anyway I have experience with the above, and a good understanding of the design from the electronics side as well as of the PSM and other stability systems in general, and what an LSD does dynamically to the car, but I have not tried to fit a diff from one car to another myself. GTgears , thanks for the info! No wonder the factory diffs don’t last long in the GT3/GT2...

Ahmet , do you have anymore detail on the programming for the PSM on the 996 40ae ? I asked about this at the dealer and they said the PSM was the same . The Motorsport tech said the limited slip diff was available as a dealer retrofit on 996s and there was no programming change requiered . my car performes very well with a 40/60 GT modified diff and standard PSM and I've not observed anything that would make me feel that it needs reprogramming .

I have never heard that the LSD was available outside of what I’ve noted, is it possible to get a reference to this in writing? Anyway, as for PSM programming, I have read about it, but I do not have any more info, nor can I find a specific reference to it. I may very well be wrong on this. I should note that with my understanding, it would make sense why Porsche would not have chosen to fit an LSD without modifying the programming (or going with a sufficiently low lock up rate). I’ve expanded on this topic in the other LSD related thread. Not saying you can’t do it, I’ve tracked a Carrera with more than 4X the factory spring rate, and it was just fabulous for example. I suspect a stronger lock up ratio with the normal PSM would just make the PSM slightly less effective when it’s intervening for stability, and maybe cause audible chatter from the LSD. It would be interesting to see if those with experience (may?) share with us that/or if the 40th AE and the late 996 turbo rear LSD are both very low lock up rate LSDs?

The one I bought was out of a crashed 40ae , it originally had 25/27 ramps . My understanding from what the dealer told me was you could get a lsd in 2004 one of 3 ways ( at least in Canada) Buy a 40 ae , order a car with the x51 power kit or have it dealer installed. Don't have it in writing , just what the chief mechanic and Motorsport tech at the dealer told me .

There is no reason not to run an lsd on a Psm equipped car. This is an ancient internet rumour that needs to be buried. We have installed them in literally of hundreds of cars. What does it do? It makes the psm less intrusive. And it makes the car faster. And it makes your brake pads last longer. But if you are a good driver you are turning it off on track already. If you are a really good driver you have killed it completely because turning it off doesn't really turn it off. It just makes it step in and save your **** later. Yes, I am Matt Monson, owner of Guard Transmission.

Thanks for clearing that up, nice to hear from an expert , the 40ae diff with guard transmission internals in my car has been a great upgrade , it's night and day a better car to drive , PSM on or off . People spend a lot of money on exhausts and air intakes chasing a couple more horsepower out of a 996 , IMO chasing deminishing returns on a motor that produces around 100bhp per litre stock. a full high end Kit is about 7k and gets you about 20hp , maybe 25 But spending money on a limited slip plated diff so you can put the power to the ground and go harder in and out of corners , now that's money well spent .

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My question was actually about which mechanical diffs you have tried and liked (especially on a Porsche). I wasn't sure whether you meant a clutch based diff, or a gear based diff, or ... . Anyway, I take it from your answer that both OEM and GT LSDs are what you have in mind. Thanks!

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I do have the bolt in axle flanges, as shown in the picture, below. (The bolt is sitting in the top of the flange in the picture, when attached to the car, it is screwed into the opposite end.) These are also used in GT3s, no? However, according to the PET, it looks like these were only used on model year 1999 and earlier C2's (as in the pictures further below). (This is how I understand "-99" in the remark column, though the text in the model column ("G96 00/01") makes me wonder.)

On the other hand, while I think I know which axle flanges I have, which diff I have is a mystery. It doesn't exactly match any of the 3 differential pictures in the PET. I'm not even 100% sure it's a Porsche diff, though it does say "Germany". But according to my local specialist, when they removed it, they were able to confirm that it is a limited slip diff, though seemingly a very mild one. Anyone recognize this? Can I send it to you (Matt) and have it upgraded? Here are two photos (the first shows the color correctly, the second is discolored by the flash):

That might be an open or geared diff it's not lsd , it doesn't look like the one in my car

That's an open diff. Late 4 spider version.

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Mine? So 4 = 2004? And spider = Boxster spider/spyder? Or ... ? In any case, thanks Matt for the help identifying it. I guess if it's open I can't send it to you to upgrade :-( And I'll have to edit my initial post too ... .

No, 4 spider has to do with how many spider gears are inside. 99-02 only had two gears. 03-04 had four because a lot of the early cars were having failures, especially on 996tt which used the same diff.

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What Vancouver996 & Matt with Guard said. I had Matt supply my tech with an upgrade kit (internals) for my 40th AE LSD; it really woke the car up. I daily drive and do about 8 DE weekends a year. It has performed flawlessly over the 3 years that I've had it.

Not to high jack the thread but is it possible to install a LSD into a car that didn't come from the factory with it? Say a 996.1?

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Yes. You can install an LSD into pretty much any 911 gearbox. There's nothing about the gearbox of an open diff versus LSD transmission that is different.

Thanks for the quick reply GTgears! Great news as well.

My car didn't have an lsd when came from the factory . I had a shop uprate a diff I bought on ebay with guard bits and install it .

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This thread is so full of LOL... Good thing the discovery was made on only page 2 instead of 10+

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Indeed. Updating original post now, so no one reads the first few posts and goes out and buys a "996.1 LSD" just like mine to replace their open diff ...

One thing still seems odd though. I have bolt-in axle flanges, and according to the PET, while there were several different types of clip-in flanges on the 996, there was only one bolt-in type, and it was only used with the "-99" limited slip differential. Is the PET wrong - are these flanges also used with some of the open differentials? Or was my diff installed incorrectly? I mentioned above the chuntering I sometimes hear in parking garages, which reminds me of other LSD equiped cars I've driven. I've recently spent a lot of time driving an almost identical 996.2, including in the same garage, with no chunter. Before suspecting I had an LSD, I therefore had the clutch checked and was told my clutch was actually in good shape, much better than the other car's. Could the wrong axle flanges be the source of the chunter?

My car drives and behaves like it has LSD, and it's not listed as a option. Either someone added it, or it was included with non-psm cars from the factory. Either way, can take a peek when we do the clutch sometime this spring or early summer.

All the clutch style LSD's I've seen allows both wheels to turn the same when you jack up both sides and try to spin one of the tires by hand. This is one way to know you have it for sure. All open diffs should spin opposite to the other.

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Not true on the more recent cars. The 987s, 981s and 991s run zero preload lsds. With no preload a casual spin of the wheels on a life it acts open.