Hi, can anyone that has retro-fitted an early 928 twin plate clutch (eg from an S2) on a later S4/GT/GTS tell me:

1. Is it best to change the clutch slave cylinder to the earlier type which is a different size?
2. Which clutch release arm to use?

Thanks

 

the twin disc clutch of the early years, IS the upgrade for the S4 and GTS

mk

 

I think the important part of the question has to do with what all is involved in the conversion. are the pressure plates the same diameter, I didn't think so. Do you have to replace the flywheel? What else?

Thanks
Rod

 

To retro-fit a late-model 928 witht he earlier twin disk, you will need the flywheel, intermediate plate and 2 disks, plus a new pilot ube and throwout bearing.

I believe some can continue to use the same release fork, while others have to change the fork too.

Jim Bailey knows which is which.

 

Why, is it stronger ??? I did the other way, cause I was told when going from 240 hp to 300+ it would not stand the power ????

 

the twin disc is stronger, with much more clamping power. all the racers usually have converted the later cars to the early clutch design for that reason. (ie joe fan, anderson, me , and others)

what is needed is an automatic flywheel from an 85 US, and then a timing gear from the S4. they need to be pressed together and tac welded so they dont move. Then, you need the entire clutch assembly for an early dual disc clutch. no mods are needed for lever arm or slave cylinder. If you go for the early bell housing, so you loose the starter mount bracket, you then need to grind away a little of the bell housing where the starter ring hits, and you need the early style slave cylinder.

not only do you get better clamping forces, you get smaller diameter of the rotating mass and much less overall weight.

mk

 

Mark,

Have you weighed the two for the difference? When I did the 5 speed conversion to the 1986.5 track car, I had to use the twin disk set to keep things simple since the 1986.5 928s came with it. I noticed the intermediate plate was heavy so I question it being lighter than the single disk set up.

I also heard there are problems sometimes setting up the twin disk to operate correctly and some have went from twin disk to single because of the simplicity. I did not have any issues with the set up personally, but I saw how one could get it wrong.

I know in racing multiple disk set ups are used to be able to reduce overall rotating mass but increase the clamping force area.

Constantine

 

yeah, i have weighed them. I have a picture of them both on the scale.
the S4 was 45lbs and the twin disc was 25lb. (or something close to this)
if you think our intermediate plate is heavy, wait until you feel the stock S4 pressure plate.
Ill see if i can dig up the picture.

mk

 

I presume you meant a manual flywheel. And it can be 85 or 86, as they are the same. At least that is what my research has indicated.

 

Good Lord! 45 lbs for a single disk S4 set up? No wonder 928 racers do the conversion!

Yes, the 85-86 and 86.5 all have the same flywheel which is different from any other year.

Constantine

 

We also can provide an aluminum flywheel for the twin disk setup with the 60-tooth or 100-tooth timing ring already on it for you.

It is here: http://www.928motorsports.com/parts/...umflywheel.php

That will lighten it up even further.

 

OH yeah, i forgot. manual flywheel, and the timing ring from he S4 automatic flywheel.
Its been a while. Ill have to check my notes. 928Intl knows how to configure it.
mk

 

adrian, chris sanderson had merry fun trying to make the clutch actuate correctly in the orange car when we were transforming it from auto to manual. we had an assemblage of parts including a 91 onwards slave and release arm and i think it is these that are in the car... but i could be wrong about the release arm.

how was your first round of racing?? nick.

 

Thanks Nick, I'll give Chris S a call re clutch.

Re first race, it was on the Brands GP circuit, which I had never been on, so quite an experience. Was second in class in race one, and was running third in class in the second race until I went into the gravel on the last lap just before Druids. No damage and was happy to go home with a trophy from the first race. Mark C was 2nd in the last race in his 928 'gts' to a 993 RS Cup car.

Quite a learning exprience! I need to rebuild the engine over the winter and get the weight of the car down to give Mark/the winner more of a challenge next year.

Rgds

 

Nick posted
My 81s (82 model year) has twin plate clutch and a GTS release arm; I only know because my arm was bent (no idea why) & when I bought a new one it did not fit. I checked the old arm & it was a GTS..

Marton