Targa Tim

Thanks Allan, but I've only done one track day on it, my LSD should still be working...

AllanJ

Maybe. Talk to Bernie next track day.

mooty

i am not all that concerned with warranty on the gear box or LSD.
i been through several oem LSD's. junk.
i put on a GT unit... bam, all done. never worry again.

mikymu

Good deal and glad to hear you have a competent tech to do the job

GTgears

5 gt3 street cars or 5 gt3 Cups? I ask because your signature is loaded with Cup Cars and it's a different LSD than the street cars get. There's no issue at all with the Cup Cars other than the change to cast inner gears in the late 996 and all 997 versions.

mooty

^ thusly has a hording problem.
he's got at least 5 cups and at least 3 street 6gt3.
and i am not counting his 997 versions.

savyboy

Yes. I take solace in knowing someone has it worse than I do...lol.

Fred- that is awesome to hear of Ted & Co. VIR win! Ted was running 2:34 out of the box at SM 3.1 with his new RS. I gave it all I had to do a 2:40! Just goes to show difference between pro and weekend hacker Inspirational for me.

PS- I was joking and certainly did not take personally or offense at your comment.

GTgears

Holy Wow. I've got a hoarding problem but it's mostly rusty old 912s and 914s.

AllanJ

lol! I had a hoarding problem with 914s too. I had 4 of them at one time.

YearOne

I do not know the ins and outs of the diff but I was told by a Porsche independent that the problem with the diff in the GT3 is that the shims are not long enough and once there is any wear the plates stop meshing. Their solution is to put shims in and this cure the problem.

I am only quoting what he said, can someone please explain this further?

GTgears

It's part of the problem, and it is a solution that some have used with good success. What he's talking about is the belleville washers. They are 1.1mm thick and have a very low crown height. So once there's any wear at all there's no pressure or contact on the discs. Part of what the belleville's do is "kick start" the locking of the diff. Putting in 1.4mm bellevilles from a Cup Car is a solution that does get greater lifespan out of the LSD.

However that's not all of it. The factory plates don't have a high enough coefficient of friction to them. They just don't bite very well. A very common misperception about how LSDs work is people think the locking percentage numbers have something to do with how much the LSD is still slipping inside. When an LSD is locked, it is locked. There should be no slipping. The locking percentage number refers to the differential in force across the drive wheels before it locks. When it's published that it's 40% locking on acceleration, what that means is that if the inside wheel on corner exit starts spinning and sees a differential of 40% versus what the outside wheel is doing, the LSD will lock and it will not unlock again until traction is regained and the diffs starts to act like an open diff again.

Because of the brass friction discs, with a minimum of wear, even with thicker bellevilles, those plates are going to slip. They aren't going to lock together the way they are supposed to. Then what happens is things get hot. Friction makes heat and the overall temperature of the box goes up, accelerating the wear on everything in there, not just the LSD. So, while the belleville fix does put off the inevitible a bit longer why would anyone paying labor do it?

Afterall, how many hours to get into the box, remove the LSD, take off the ring gear and replace the bellevilles? Why would someone go that far and not replace those brass discs with something superior? It's another +/_$600 in parts to do the full service on the thing. It's kind of like doing an RMS replacement and not changing the clutch while you're in there. You can do it, and under certain circumstances you won't want to take that extra step, but I think for most people who pay for their labor it's just not cost effective to make that change without going all the way through with a rebuild.

thusly

Not quite that bad...... 5 street GT-3s (no more), and 2 996 Cups (one current), 1 996 RSR....

That said, and presuming parts are crap, what are the reasons why diffs go? Is autocrossing harder on diffs that road courses? Just curious.

NJ-GT

Fred, the sharper (or tighter) the turns, the more the diff works. I think that autocrossing wear out a diff much more than a racetrack. Being in 2nd gear at full gas out of most turns generates a lot of torque and make the LSD work harder. A good autocross course doesn't have a single straight.

The housing in the stock street GT3 is good (per Brian Copans), the internals are garbage.

thusly

Thanks!!!! I would imagine the autocross situation is exacerbated with stickier tires too.

mooty

OH, i see.
you can still be saved

i have been to re-hab.
i am well.