VAGscum,
My apologies if you think I have turned your thread into a shytestorm. That was not my intention, nor was it my intention to insult you. My comments were more pre-emptive than anything else and I'm sorry if that came across as accusatory. I've just been around this board long enough to see what I consider a significant anti-vendor bias because so many of the vendors so aggressively push their products. But I was also not trying to be overly serious about it in tone, and thus the Norelco joke. I just wanted it to be very clear that my opinion is based on what I think the right answer is and not what makes me money.

I also want to clarify some of the above comments. I have seen 7 catastrophic gear failures on GT2s. I know of more catatstrophic gear failures on OS Giken LSDs than that. I never meant to send the message that there is some spectre out there of the magnitude of the 2nd gear popout issue or the IMS issues that is just around the corner waiting to bite everyone in the ****. I made an assumption about your vehicle when I made my comments. I don't honestly know your power levels, but considering the direction of your build I felt it safe to assume that they are more than stock.

Stock GT2s are blowing up the spider gears. Stock GT3s are bluing the plates. You responded that your plates aren't blue and look fine. What I am trying to tell you is that if you do not do something to improve that unit you have purchased, they are going to turn blue and get hot. I don't consider it a question of if more than a when, assuming that the car is driven hard. Are you going to blow up the gears? If it is not tracked, probably not. I only present it as a potential risk.

My only other comment is that I am going to reiterate engaging the guys in the LSD Buster thread. The reason for this is that there was only a factory LSD in the very end of the 996tt production. I can probably count the number of factory 996TT LSDs I've had through here on one hand. I don't think there are very many readers here who have direct experience with what you want to discuss. The guys in the LSD buster thread all have LSDs in their cars. And if there are people who have experimented with the stock factory plates you are more likely to find them there and not here.

With that said, you know my opinion on the subject. I don't want to take over your thread and dominate it. That's not nice. So if you want further feedback from me, just ping me with a PM either directly asking the question or letting me know there's something here in the thread you would like my input on. Otherwise I will stay silent and not intervene. I feel it only the respectful thing to do.

 

See above ^^^

 

VAGscum,
I know you appreciate my input, though I thank you for saying it out loud. I just don't want your thread to become the Matt Monson show.

The problem is that as I mentioned above there are 1.15mm bell washers in there and the next available size is 1.8mm. There are 2.0mm steel plates in there and the only thinner size made is 1.4mm, which Porsche only sells as part of the complete Cup Cup vane kit. Or we make and sell a 1.0mm, which is too thin.

However, I got a call from Paul Guard this morning. For some bizarre reason he has been IP banned from the site. He can view but not log in. Never got a warning or anything. Anyway, he called to throw out an idea.

Our clutches are 2.1mm. The factory brass ones are 2.7mm. So, you lose .6mm per side if you replace one of the OEM clutches with one of ours. Then, you replace the 1.15mm bell washer with a 1.8mm bell washer, a net increase of .65mm per side. Total, you would change the stack height by .1mm tighter and increase both the preload and the coefficient of friction because you have changed to a bell. washer with more spring rate and to one of our discs which has more bite. We don't honestly know how it would drive or wear. It was just a random idea Paul had. It was a way to get to a reasonable stack height and increase the functionality of the LSD without going the full monty. Something to think about.

 

That is a creative idea. The housing internal space is 95MM. The current stack up minus cup washers is 92mm leaving a total gap of 3mm or 1.5mm per side. What is the target internnal gap to utilize the upgraded cup washer?

 

You are going to want to measure everything again. I have NEVER seen a body and end cover that measure anything outside of 94.5-94.6mm, except for an RSR LSD. And even then, if your numbers are correct that's going to be one of the tightest units I've ever seen come out of the factory, unless it's already been fiddled with.

The average gap I see on a GT3 LSDs is in the 2.0-2.3mm total internal gap range. You are talking about a diff there in your possession that is .3-.7mm total internal gap. Most of the diffs I've done in the LSD Buster thread are between 1.4mm and 1.8mm total internal gap. I only go tighter than that on the dedicated track cars and race cars.

 

I just re-measured 5 times and I was a little off orignally. The internal space from the inside cover to other side is 95.25mm. The stack height is 92mm. So 3.24mm total gap. This is by reading the height of the vanes only no thrust washers or cup washers.

This LSD is a 993 body (PN: 950-332-083-01)with GT3 internals. It was originally a dual carbon disk setup. All of the original tooling marks are there. No fooling around other than the vanes.

Are you adjusting internal gap to reach a target preload/static breakaway torque?

 

You are saying that total gap meaning gap on one side of the vanes plus the gap on the opposing side?

 

I have the original carbon stackup and it was originally 91mm.

 

Don't subtract the bell. washers. They take up space right? My gap measurements always include washers.

But I understand now what is going on. 993 LSDs were on average 1 to 1.5mm thicker pressure rings than gt3 pressure rings. This is part of the problems with Porsche's one size fits all approach. The carbon frictions were generally around 2.4-2.5mm whereas the brass ones are 2.7mm. That's why it's so much tighter than I expected.

 

So you measure the highest point of the cup washers when relaxed or do you just account for the thickness of the metal on the cup washer?

 

You only measure and account for the actual thickness of the washer. And this is part of why a Porsche Motorsports 1.8mm bell. washer will be slightly different than a GT 1.8mm bell washer. Ours have more crown height, and therefore more spring rate, introducing more preload.

I missed this one last night. The answer is no. I won't even put a torque wrench on a customer's LSD. The number gets given ridiculously too much attention. I can build an LSD 6 different ways to get the same end number.

Saying you've got 60ft/lb of preload on your diff is about as useful in my book as saying that you run 25.5" tires. Are they Hoosiers? Are they Michelins? Are they 17's or are they 18's? I think you get the point. If I've got 1.4mm of internal gap and have used 2.2mm bell washers, that might show the same breakaway torque number as a 1.1mm internal gap with 1.9mm bell washers, but those two LSDs will behave very differently on track when someone is racing on them. The preload number is an outdated metric that I feel gets given way too much emphasis in LSD conversations. And that doesn't even take into account ramp selection.

FYI, in case you don't already know it, what you have there should be 25/65 ramps. Really a pretty nice set up for a street rod, though if you ever take the car out to a Friday night drag event it may have a bit more one wheel spin on launch than is desireable for the best ET. Though I don't know if that is your thing or not.

 

Too much wheelspin as is in not enough lockup causing one side to spin?

The goal is to be able to do a few road course track education events to learn and drive mostly on the street. I will not drag race this car ever.

For the cup washers, these are the stock 1.12 mm washers which gives a gap of 1.01mm gap? They seem really flimsy a like they would flatten out permanently after a short period of time. So 1.8mm washers will require adding~.675mm of gap (thinner steel plates)per side if the original gap with cup washers remains?