Adjusting 930 LSD power/overrun split.

[Bill Musarra]

Gregg,
I know some of the people here on the forum had a bad experience with David. I however didn't. My purchase of a 930 from him was fraught with problems which I do believe were coincidental. He honored his commitment and made everything right. Tried to give me outs all along the way, but I persisted and eventually got what I wanted. see:

http://www.gt40s.com/forum/gt40-tech-powertrain-transaxles/18166-930-saga.html?highlight=930+saga

He demonstrated a knowledge that was far beyond mine,but you have to remember I have only minuscule knowledge of the Porsche products. He did show that he knew some things my shop foreman was unaware of. That isn't to say he was dumb or uninformed. To be shop foreman in the Atlanta area Porsche dealer is no small feat. They undergo constant training updates all the time and would have to be pretty knowledgeable to attain that position.


Russ,
According to the shop foreman, The slip is controlled by the thickness of the disc. they come in four sizes from about 1.8. 1.9 etc. Which way it goes I have no idea. Maybe someone else can chime in.

Bill

 

[Russ Noble]

Thanks Bill. I think I've pretty much got it sussed now. To recap for anyone following this thread....

The early trans are set up square at 40/40 or 80/80 depending on the arrangement of the plates. With the 40% setup the driven plates are stacked together adjacent to each other, in the 80% set up each driven plates is separated by a drive plate. Drive plates are available in three thickness (1.9, 2.0 and 2.1) to enable the action to be set up to factory spec. Driven discs were also originally available in these three size also but now NLA, and the three now supercede to part # 951.332.551.00 .

The official Porsche line is that when you use the superceded plates you need to also change out the two thrust plates/spider carriers. I think this is a load of bollocks and at about $NZ400 each here in Godzone there's not much chance of me doing that if I don't have to! The only reason I can think of why they say to change the thrusts is if the friction coefficient is different and they have altered the ramp angles to compensate. I will update on that one later.

For the later trans set up with an assymetrical split. This is achieved by changing the aforementioned thrust washers to ones with different ramp angles. A shallower ramp provides greater clamping force. If you have one of those and you want to change from the Porsche split (say 80/20) to a GT40 split (say20/80) all you have to do is swap the thrust plates from side to side. If you want to vary your split ratio you change your thrust plates to ones with the desired ramp angle. QED

Thanks to all the guys that contributed to this exercise.

 

[Russ Noble]

The official Porsche line is that when you use the superceded plates you need to also change out the two thrust plates/spider carriers. I think this is a load of bollocks and at about $NZ400 each here in Godzone there's not much chance of me doing that if I don't have to! The only reason I can think of why they say to change the thrusts is if the friction coefficient is different and they have altered the ramp angles to compensate. I will update on that one later.

THICK that's what I am!

Same as the superceded plates!

The new plates are 2.5 thick, the old ones were 2.0. That's the difference. This locks the diff up solid! I got four new plates from forum member Ryan at gboxweb.com, good service, good price.

I wound up using the two old 2.0 plates since they had no wear and two of the new thick ones. That gave an extra 1mm crush on the slip so I backed the clamping bolts off until I achieved my desired breakaway torque and measured the resulting gap at 0.33mm and surface ground (well Lim did!) this amount off the thrustplate/carriers . Bolted it all up and it was still slightly tight so decided to surface off another 0.05mm (.002") This produced an amazingly large drop off in the breakaway torque and brought it down to slightly less than I wanted. Still at the top end of the spec though so should be good. So I've now got an 80/80 slip. :thumbsup:

Interestingly, to adjust the breakaway torque the factory way, Porsche supply different thickness drive plates in 0.1 mm increments. So my 0.05 increment is a finer adjustment.

The way Porsche set up their r&p is dead simple too. We're just about to make up a couple of tools equivalent to the much vaunted official Porsche service tool (VW385) so I can get the setup spot on.

Really I've got to say the 930 trans is easy to work on and setup and the essential parts are a lot cheaper than I ever expected.








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[Ross Nicol]

Well Russ You know I can't go along with you on the cost of the good old P****** parts. The wider you open your cheque book and the more zeros added, the faster you go you know. My bet is you'll either be spinning up your inside wheel or pushed into understeer as Ross and his ZF go sailing by at Teretonga next Feb. Just keep adding the variables my man.
Ross:thumbsup:

 

[Russ Noble]

Talk about rose tinted glasses Ross! :stunned:

When the flag drops the BS stops!

Just as well you've got a car cam, you'll get some good shots of my 930 before it vanishes into the distance, but that'll be my 4bbl dealing to your Motec! :thumbsup:

Haha Ross, you know I'm not a cheque book racer! FWIW my 930 will owe me about $NZ4500, That's NZ dollars, you know what they're worth! And my super trick BG RS 4bbl about $NZ600. What's the new RBT and Motec worth? What does it cost to rebuild 2nd gear all the time?

Sorry mate I couldn't help myself. :devil:

With all these expectations one of us is going to be wearing egg on our face next year. We should see if we can make some money out of side bets.:thumbsup:

Cheers and good luck for your next meetingepper: