OldGuy

Kaizu are you saying we arent testing it correctly and the LSD might still be Good?

mikymu

Beats me why Porsche use such a crappy LSD in a track oriented GT3/RS. The only reason I can think of is perhaps Porsche want to dial out oversteer from a working LSD to make it relatively easy and forgiving to drive on the track - but kills lap time

The one wheel off test I demonstrated will not tell you the exact left over preload of your LSD but this is a very quick indicator of the health of your LSD's preload. I did the one wheel off test on a 6 GT3 with a completely dead LSD and you can easily spin it with a gent push compare with my LSD which only has 20% of preload left and you can hardly turn the wheel on a freshly rebuild LSD - you get the point. To get the exact preload readout you need to remove the LSD and test it on a bench.

Other on the road/track indicators of a bad LSD are:

• Spin an inside wheel on corner exit
• Rear end wag during hard braking from 100mph+
• Black ice test by NJ-GT. "Do a moderate take off with one rear wheel on a decently long ice patch(or water), and the other on dry pavement, if you see skid marks on the ice patch and nothing on the dry pavement, well that's a 1WD GT3 you got" lol

enthusiast

The static load torque is so low most people would not be able to tell anything from the 'one wheel off test'. If they tried it on a new car they would be think they have no LSD.

Concur that road/track tests are best indicator on health of LSD while assembled.

See the FAQ I posted.

mikymu

Yes, that was a very informative post!

The one wheel off test is useful if you have a good reference point. I did this test on another RS with intact OEM LSD and it had significantly more resistance than my LSD which has lost 80% of it's preload. I can barely turn my wheel with the rebuild LSD. The next step is do a NJ-GT "black ice" road test or brisk stop track test if you think your LSD is gone.

GTgears

I figured I would update this information here since this has kind of become the GT3 LSD resource thread. I just got in the first 2010 GT3 LSD that I've seen so far. Same part number as before. Same ramps as before. Pretty much the same thing. There's no change for 2010.

I also found some damage that I haven't seen before. I'll post pictures tomorrow. People frequently question why our gears and other parts cost what they do. A large part of it is because everything we make is from cnc billet. When I show you pictures of the cast factory ramps and what happened to them on just a couple thousand miles you'll see the difference between cast and billet.

ADias

Interesting.

mikymu

WOW! Porsche continue to put crappy LSD in GT3 ... not surprised. I thought they said something to the fact that they are using an improved LSD. I guess not.

2010 GT3 Spec

"Transmission Standard Features
6-speed Manual Transmission - With double inertia flywheel and transmission oil cooling
Limited slip differential - With asymmetrical locking action - 28% on acceleration/40% on deceleration
Hydraulic clutch actuation"

GTgears

So here's a few photos for your review:

See the chip? See the hairline crack on the upper side that suggests that one is about to break off as well? At first I thought it was some weird fluke. But it's on 3 of the 4 posts!!!

Also, here's what the gears look like. See the pitting? The crazy thing is that I have brand few OEM LSDs showing the same inconsistencies in the gears. The spider gears are going to be the next thing to go on these LSDs. And this is one thing that's no different on a motorsports LSD. The same gears are used.


Lastly, I want to show you what happens when these get driven hard and are really done. While the mileage on this car is very low, this owner pretty much tracks the car and not a lot else. For reference, Mikymu's LSD had an internal gap of less than 1.6mm. That's pretty typical. I see them from a low of 1.3 or 1.4mm when brand new to around 2.0mm when worn out. This particular LSD had a 2.8mm gap!!!

And this is what happens with that gap. It gets hot. It gets really hot because the plates are just spinning in there and not biting on each other. This is what happens if you keep driving on it once it's worn out.

GTgears

Oh, and one other thing that I almost forgot to mention. A couple of weeks ago someone involved with an ALMS team told me that they were starting to see these broken ramps on the Cup Cars that they are racing. I was skeptical as I hadn't seen any through here with that problem. But with this one and having now seen it first hand, I could see how it would be a problem. Those little pieces of metal are going through the gearbox on their way to plug. Imagine what happens if that rolls between a couple of gear teeth or gets between the slider and synchro when you attempt to make a shift!!!

cfjan

Matt,

In the past you have mentioned that the ramp shape on the 996 GT3 (and older) are actually okay and usually you just recommend people to put in the Guard internals. But it would seems that even w/ the proper (relatively) shape ramp, the fact that they are not billet might present a problem?

TTurbine

Matt , these look awfull!! i cant beleive i was driving it!! If it was not for this thread i would still be driving the cars hard... until the chipped parts find there way in the gearbox ...... are these the GT3 or GT2s LSD?

If its the GT3s , it only saw 2 track days!! , While the GT2 had 3 track days only... all of them hav about 6000 miles on them!!

Where the damage similar on both? i guess the GT2s lsd would be the one with most damage since it had higher hp and tourqe than the GT3 ?

GTgears

You know, you present an idea that I hadn't considered. You may very well be correct in that thinking. It would also explain why only very recent Cup Cars have encountered the problem, because if anyone was going to be breaking and chipping the ramps it would be the pro teams and PCA hardcores.

Maybe it's related more to the steepness of the angle where the post hits the ramp and maybe something as simple as a chamfered edge on it might stop the chipping.

TTurbine,
The GT3 was the only one of the two that was "smoked" and chipped like that. The GT2 LSD was worn out but didn't show anything weird.

cfjan

Yeah, with a less steep ramp it might not be hit w/ such a strong force upon lockup right at the edge.. ?!

GTgears

And if you look at the old turbo ramps that were 20% (versus the current 28%) while they were really steep, they didn't have the curvature that the current ones do. There was never a problem with those ones. Maybe it's a design issue versus a materials issue, but it appears that either way it's an issue to look out for...

cfjan

So it is probably recommended that when the diff is out, instead of just changing the plates inside, you guys would start to recommend changing the ramp too? (obviously that adds to the cost..)

Or you would still recommending the 996 and older LSD to keep the stock ramp?