GTgears

A couple of comments in no particular order and without quoting anyone, so I am sure I will miss something...

The 997 Carreras use an Aisin gearbox that is quite different than the Getrag box in the GT3s and 996 Turbos. In my experience the factory LSD in the Aisins is actually a pretty robust and durable and well functioning LSD. This is in direct contrast to the GT3 LSD which has crap clutches and works poorly from day one.

I only have the aftersales manual for the 997 and it does not show the test for the LSD. I apologise for no knowing the breakaway test number, but suspect it is found in the tranny module on the complete 997 FSM. One cannot use the GT3 numbers for this LSD.

It is a low preload unit and spinning the wheels doesn't reveal much because it doesn't go active without a pretty good slip event (load) on it. It also will not provide the same rear end under braking stability that a motorsports LSD does because it lacks that preload. This point is important.

My inclination is that it isn't so much that your LSD is worn out as your racecraft has progressed to the point where you are braking harder and later and revealing the performance weakness on the LSD. The unfortunate thing is we don't have a fix for you like we do for the GT3s. We rebuild GT3s. So few Carreras got LSDs is was never cost effective to make parts for them. We only manufacture a new LSD for it.

Lastly, Giken is not a gear driven diff. It is a clutch type LSD. Quaife and Wavetrac make the gear driven torsen gleason designs differentials (we make one too, in addition to our LSD).

All of that said, if you can get a brand new Aisin LSD under your warranty, I have no doubt you will see an improvement in performance. You have a lot of track miles on your unit and it is probably tired. Is it to blame for the wiggle? Not really a definitive answer there, but overall a new LSD at this point in your vehicle's life would benefit your track performance. That piece of it I am confident of...

exgtinows4

Thank you! Valuable information. One question- which aftermarket diff can improve performance on the GTS and work with PSM? I understand that most don't.....

nwGTS

Oh man that info is gold. Thank you!

1990nein

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GTgears

Sorry for the slow reply. Not around much these days as business is going nuts.

There's a lot of confusion and misinformation about the PSM. In one respect the LSD makes the PSM less intrusive. Fact of the matter is the warnings about running an LSD with PSM comes largely from LSD makers not really understanding what is happening and putting it out there as a CYA liability thing.

The LSD makes the ABS/ABD portion of the PSM system less active. The LSD handles differences in traction before the system kicks in.

But here's where the PSM issues become worse with an LSD. And it becomes compounded more if you are running sticky tires. Part of the PSM is based on the yaw sensor. When it thinks you've gotten too far out there, it will reel you back in. This is true even if you turn off PSM on track. The yaw sensor protections are still there. An LSD increases your traction and your corner speed, and ultimately your mid-corner Gs. And LSD makes it easier to set off the yaw sensor and have PSM jump in just when you don't want it to.

Two solutions. Unplug the ABS and run without ABS. Or kill the yaw sensor when on track. This requires cutting the wire and putting a switch in place so you can disable it on track.

In short, if you insist on driving on track with PSM on, at some point your skill will exceed what the car thinks it can do (even though it can do more) and PSM will intervene.

Cloudspin

For those that don't know, GTgears is the proprietor of Guard Transmission, the manufacturer of the Guard LSD and many other driveline enhancement products for Porsches. Guard makes three flavors of LSDs for 997s depending on transmission type:
6MT
PDK with factory LSD
PDK without factory LSD

I've been very pleased with the two Guard LSDs I've had in my 997.2s, both of which were PDK and Matt was a huge help when I was investigating and looking to purchase both of them.