exgtinows4

Folks, here is a situation that I am in and I would love your advice (hopefully based on first hand experience or technical knowledge) -

1) The GTS comes with a mechanical LSD that is largely known to wear out pretty quickly. I have 30K miles on mine and some track use too. I have noticed that under hard braking I get rear end wriggle/instability which I believe is something that a working LSD is supposed to avoid.
2) There is not test that can confirm that LSD is working or not -without taking it apart
3) I have a extended warranty that covers my LSD.

With all of this, I took my car to a shop and have them call in my warranty company. The company is fine with covering, but needs a tear down (on my dime if its not broken).

So, here are the questions -

1) Do you have any insights/knowledge of how to test a LSD for working 100%? without taking it apart?
2) Any specific knowledge on wear down of the LSD on the GTS? Does 30K miles with 10 track days seem like it would do it?
3) Should I move forward with the tear down and take the risk of 4 hrs of labour?
4) Will a OS Giken unit work with the factory gearbox / PSM? I have heard some conflicting information on this
5) any other advice :-)

thanks!!

DC911S

Thats from your rear suspension loading and unloading, nothing to do with the LSD. Your rear rebound is too slow. If the LSD is a clutch pack kind, then yes it can wear out. Not sure if the LSD in the GTS is clutch based or helical based (gears like the Gilken).

alexb76

I don't think your situation is LSD problem, I wouldn't worry about it at all. 30K miles and 10 track days shouldn't do it. I would probably wait until maybe 1 month prior to your warranty expiry to risk such an experiment...

To identify if LSD is working or not, you need to be experienced and try to lose traction in one wheel and see how the other wheel reacts. Maybe in your next track day ask an experienced instructor to drive the car to see if the LSD engages or not?

nwGTS

Head over to the GT3 section and do a search. There's a lot of info on Guards diffs as replacements and IDing. Not sure why DC911S thinks this can't be LSD related because rear end squirm under hard braking is definitely a symptom of an open diff. It CAN be your rear suspension preload but these OEM diffs are known to blow open on only one or two track days.

To answer your questions:
1) On some LSDs yes you can diagnose without opening the diff but not on the ones in our cars. One option I've heard is to jack one rear tire with ebrake off and trans in neutral. If you can spin the rear wheel freely (with other rear wheel on the ground) then the diff is open. I've also heard this doesn't work on our diffs. Sorry if this isn't any help. I've mostly heard that ours need to be disassembled to tell if they are worn open or not.

2) Yup, that would definitely do it

3) If you track the car extensively replacing with an OEM diff is a bad idea. Might last you another 10 or so track days and blow open again. If I were to have them go to the trouble even under warranty of opening my diff I'd just pony up and get the guards diff. This also depends on how long you are going to keep the car. If 4 hours labor is the only thing I'd be out to find out it's fine though, yeah I'd do it and replace it with a guards diff anyway.

4) Ask the 997 GT3 forum. Lots of threads and knowledgeable dudes on diffs in these cars.

5) Go guards over giken is what I hear from others.


I'm still on my original OEM diff but think its going to blow open this year. After that, I'm going guards.

exgtinows4

nwGTS - the test you mention - I tried- and its open. But my shop (based on research) tells me that the diff is not a linear one in these cars - without load its open and it needs load on the wheels to be actually engaged....so that test according to them - does not apply.

Hella-Buggin'

I had a similar rare end wiggle during high speed braking on the track and it turned out I had fried my rear brake pads and they were inadequately balancing the braking weight.

Five12Free

It's true that test doesn't work all the time... another old fashioned test was jacking up both drive wheels and spinning one wheel. If the other spins the opposite way, no limited slip. However, doesn't work on all limited slips.

You could always do a couple burn outs

1990nein

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snake eyes

Do we have any documentation of someone loosing their diff on street tires? I'm curious...
Track my car and haven't had any problems with the factory diff..
2 GTS same as the 4s / 4 GTS Diff I assume.

exgtinows4

unfortunately on the west coast. Perhaps you can describe the test? Thx

TxBob74

Snake eyes, does your GTS have the LSD option? Mine does because of the Sport Suspension (P17) option.

I haven't tracked my GTS and haven't noticed LSD performance problems.

ZCPSnob

Rear end squirm under hard braking can also be caused by the giant engine hanging off behind the rear axle and wanting to rotate forward. It's physics...

nwGTS

That's exactly what I've heard too which is why I added that caveat.

Gene K

Forgive me because I'm not super familiar with this diff but couldn't you just go round and round in a parking lot with everything off and try to spin the inside tire? In my experience its pretty easy to do that with an open diff. With an LSD the rear axle will either drift out or you will push the front end.

Disclaimer: I'm not a current Porsche Owner. I joined because I'm currently in the market for one.

Macster

Experienced severe rear end squirm in my 996 Turbo under hard braking from high speed and the problem turned out to be a low rear tire. Found a couple of nails in it and as a result the tire had a slow leak.