BC

I have learned alot over the last decade.

My first 928 was an 89S4 that I bought in October of 2000. My good friend Sterling down in the Big D helped me check that car out.

I admittedly have much much more to learn about alot of stuff, but I think I can safely say that I am sure of one thing:

I no longer wish to have dual disk clutches on any of my own cars. I would almost rather have an automatic. And I don't like automatics. I break them. About 9 or so since I was 16, on all kinds of cars.

So - How does one make an S4-like Single Disk system work on an earlier block? (I have an 89 block - so thats no problem - but I also have a 5L 86 block and a 4.5L block for other projects).

The S4 flywheel is heavy. Is that because the starter ring is on it whereas the Dual Disk has it on the intermediate plate?

Are there any S4 flywheel lightweight options? Is it possible?

Is that the only part that makes it so much lighter than the DD clutch?

The pressure plate - everyone says the pressure is higher on the DD. - So I have seen we can get a high pressure PP on an S4 system - this is true right?

I have a NEW DD system sitting on the shelf. I was going to use it for either an innitial clutch for the 78(89 motor) boost build, or on a race car I have in my head. I may sell it. It includes the "worth its weight in silver" intermediate plate - also new and unused. That set is probably worth at least 1500 dollars all together - what can I get for that in the S4 clutch world?

Seriously - I'm done. With DD clutches that is.

dprantl

Why is that? I'm just about done pulling out the single-disc in my GT and retrofitting the DD in there. I can tell you the pedal effort of the DD is much less than the SD. Also, the car revs up and down much faster than before due to the lighter/smaller flywheel. The flywheel is lighter because it has a smaller diameter. Usually the problems with the DD is the adjustment on the intermediate plate. Once you stare at it for a couple of minutes while you release the clutch with a prybar it should be self-explanatory how to adjust it.

Some people here have gone with Spec's SD clutches, but they have not had very good things to say about them with regards to streetability. You can see the prices here:

http://www.specclutch.com/cars/Porsche/928/1991/Single

Dan
'91 928GT S/C 475hp/460lb.ft

svp928

What did a poor DD clutch do to you to deserve that kind of disrespect?

Seriously, a single disc that can hold 500 hp will be a leg-breaker. I had one a hot 427, and you needed to fasten the seatbelt to get enough leverage to push in the pedal. Otherwise, it would just jack you into the roof and shorten your neck about 2 inches.... and no, it didn't jist push the 2 inches out the bottom, into your pecker...

BC

I'm really not that new to the game here Dan. I know the DD clutch has a lighter flywheel and people seem to gravitate towards it.

The IP and the entire design are just ridiculous, when you compare it to the fact that I never ONCE had to go into the S4 clutch. NOT ONCE. But with DD, you will eventually have to go in there and move those stupid little T-s. And then if the center shaft wears, or the release bearing gets crunchy, you are back in. I have adjusted DD clutches over and over again on about 5 different cars. I adjust it the proper way - the question is whether it stays in that adjustment or works for 50 feet. Why the hassle?

I don't give a **** about pedal effort. That's what the helper spring is for, and your left leg. I am 6'3" and 255. I don't have any issues with clutch weight. When I go to a lighter clutch car it becomes irritating that I can't rest my foot there sometimes.

Can I have your old GT clutch so I can study it? At least the flywheel. I think I can get a lighter one made.

BC

I believe you that the SD clutch will be a bit tougher. I don't see why I can't put a tougher spring in the helper spring under the dash if I pansy out and can't do it myself.

I don't need one to hold 500. I will need one to hold 850 if everything works on the 78 properly.

You know GM has hydraulic throw out bearings in their normal daily driver LS1 cars. They don't even have a clutch arm do they?

Giovanni

I got an early DD clutch in my car and I miss the heavy pedal feel of the single clutch (although I am not complaining). The clutch pedal is extremely light, almost like driving a manual econo car. The single stock clutch could not handle 400 rwhp, the DD does it easily. Oh, and I noticed a HUGE improvement in the throttle response to.

dprantl

You may want to chat with Mike Simard. He has a generic dual-disc setup and converted to the hydraulic slave that fits around the clutch shaft, no release arm or bearing required.

Dan
'91 928GT S/C 475hp/460lb.ft

svp928

Brendan, obviously, 850 will be even worse as far pedal pressure goes, and really, the DD setup is far better suited to big horsepower- even may end up needing a 4 or 5 disc Tilton or some such. I believe the Z06 is a DD, for this reason. I understand the fiddly-ness of the stock unit- but mine has been in there for 10 years with ever adjusting it...?
OTOH, I think Carl Fausett has a flywheel made, and knows enough about clutches for our cars that you might have a conv. with him. A single disc for 850hp is going to be monstrous in size and weight to get enough surface area... And Mike Simard is good guy to talk to as well. I don't know how his car hasn't torn itself in half with the engine he built..
Just my.02...

Steve
I do wish you luck, there, buddy.

Landseer

Brendan, I just moved the T's to the back and left it.

My setup has everything new, including I-plate, like what is on your shelf.
I think it cost $1650 or so. Lots of money.
But it works pretty well.

BC

I just moved the Ts back as well. Now something else is catching the disk(s) when its not supposed to be. Maybe the center shaft, maybe the throwout bearing.

BC

I emailed Mike Simard. Maybe he will tell me what he did.

I'm sure the DD clutch on the ZR1 works just fine with no fiddling.

BC

Forgive my ignorance - why would a SD clutch be harder to operate than a DD clutch? The leverage?

Mike Simard

B', you really should give DDs another thought.
I know you had an adjustment issues and feel that it's a problem you'll always have with the DD. I had the same thing when I finished my 79 racer, I had to crawl under the car and fiddle with those T thingies and it was annoying and didn't seem normal.
After doing that once the car made it through a year of track, time trials and w2w with no problems. It wound up being the one thing on the car that didn't cause grief. It came out of the car still looking near new too.

Now I have this:
http://simardracing.com/Flywheel.html
It's nice way to use 7.25 racing clutches. I also like to use the 7.25 Tilton cerametallics in twin form for street driving too. The hydraulic throwout bearing is superior in that there's no wasted travel from linkage flex, it's very direct.

That may be the ultimate setup but it's not a huge improvement over the Porsche DD. The Porsche DD is one of those things that you may think needs to be upgraded because that's what you do when modifying a car but you find later was better than you could have imagined, the 928 is full of those treats!

To use an early clutch in an S4, a dowel hole needs to be drilled and timing ring mounted. I made a fixture to mount a ring relative to the new dowel hole and have done a couple of those although it's not a good way of me spending my time.
I think it's one of the best mods to do to an S4 and it's with Porsche parts! It makes a lighter, more nimble feeling car. The S4 clutch is so damn heavy that acceleration times and power must be measurably better.

svp928

With multi-disc clutch, you have much more surface area for friction, so it doesn't require as much pressure to keep them from slipping. This is why motorcycles have always been multidisc- because your fingers are all the force available to release the pressure plate. The more discs, the less pressure required to clamp them. Consider that 5 inch 6disc is enough to hold onto a Nascar engine...

I asked the local Z06 expert what they are doing, and he says most cars have 2 or 3 disc setups from Tilton, Exedy, etc., and this is good for over 1000hp. Too bad we can't just swap drivelines...

svp928

Mike, I see you replied while I was trying to type...lol..
I like the hyd throw-out brg. Think it has enough travel for a stock DD setup?