Clutch

[Demps]

I'm not so sure I want to open the back-and-forth expert discussion but this may help some of us non-experts. I would like to offer my observations on installing two different clutches in the same car.

The car: '91 SGC 350 with 400rwhp thru B&B with pup cats and x-pipe. Car is my HPDE car. It has a Fidanza, Hurst short shifter, RC injectors and a lot of other mods not pertinent to this discussion.

Initial problem: clutch went out at VIR.

Diagnosis: throw out bearing failure or disk material separation. The car had mostly sat for ~2 years prior.

1st solution: Carolina clutch stage 2 with LT1/4 pressure plate and "green" throw out bearing.
Result: a very grabby clutch that shuddered moderately on progressive take up/let-out AND action at the very top (top inch) of the clutch pedal. The sprung hub disk dampened most gear rattle at idle and under a bogged load (gear-high acceleration). The clutch held up fine on road course. Clamping force was always suspect. It finally slipped on the drag strip at BG to the point it was done.

2nd solution: back to stock Valeo disk and LT5 pressure plate with US throw out bearing.
Result: a stock clutch and accompanying feel--smooth progressive engagement/release at bottom of pedal travel. The solid disk allows light gear rattle at idle and moderate whine under bogged load. Still breaking clutch in so assumption of stock clutch performance will hopefully be validated with time.

Observations: stage 2 disk nominal thickness at take out was 0.285. Valeo was 0.305 at installation. The diaphragm spring and material in LT5 PP had more to it--while I didn't measure it, Jim Jandik (PowerTorque) referenced +10% and in my setup I'd say he is conservative. I was moving quickly so I eye-balled the stage 2 disk on LT1/4 PP--about 1/3-1/4 of disk material outside of PP mounts. Valeo & LT5 PP--over 1/2 of disk thickness outside PP mounts.

Conclusions: stage 2 disk may be a good option for some but it let me down in my application. It was difficult to control engine revs on road course with release at top of pedal. There is a critically small margin of travel between flywheel and PP. If quality control is good, I think the stage 2 disk & LT5 PP would be a good option for performance applications. I think RAM is next. I am very pleased in going back to stock setup.

Ted

[Paul Workman]

Interesting comparison.

You mention RAM, and I believe they have both the dual and single disc variety to fit our application. I've experienced neither the Carolina stage 2 (except perhaps for a short drive in Pete's car when he had a "puck" type performance disc) nor either of the RAM offerings, but I know Pete has a dual disc RAM, as does Bob G and Al. It would be interesting to get their perspective - long as we're comparing notes.

As for me, I've got the Fidanza, the stock Veleo (Duralast/AutoZone) LT5 PP, USA made TB, needle bearing pilot bushing, and a Center Force sprung hub disc (#381039). It has a stock feel with regard to take-up i.e., top 1/3 of travel.

I've got Accel injectors and idle at approx 750-800 (reading the tach which as been calibrated). There is very slight gear rattle at idle if any at all (according to others and a video clip I can show for comparison if anyone is interested). As for lugging in high gear - I can't say I do that much, so cannot comment now until I try it. My dyno sheet indicates 432 hp at the wheels, and I've made less than a dozen passes in the 1/4 mile contest on this current disc.

The clutch is "perfect" for my driving - I'd call very limited drag racing, but mostly some spirited twisties as always being my favorite venue (never done a road course (yet)). And, because the Veleo is no longer made, I'll admit to babying the clutch some while keeping an eye out for a good alternative.

Good to know. As we're all constantly on the lookout for better "stuff" to keep these beasts on a leash, thanks for posting your experiences, Demps.

[mike100]

So would you say the pedal engagement being high was due to different geometry in the pressure plate fulcrum movement, or from friction material thickness?
Sometimes when changing flywheels and clutch types to all aftermarket I have experienced so much tolerance stack up that the clutch engagement was in the wrong spot, so to speak. I have never tried anything different in a Corvette though.

[Demps]

I think a combination of things caused the pedal engagement and issues. I also learned a few things in the process.

The lower clamping force of the LT1/4 PP caused an earlier release. The thinner disk subtracted significantly more. I didn't measure the Fidanza against a dual mass flywheel but I'd bet it is slightly different. Like you said, changing multiple pieces with different tolerances is sure to offer issues. Real issue is, minus tolerance measurements and quality parts, the average home garage mechanic has to put it all together to ops check it.

I think there are better alternatives for higher hp applications than unsprung hub, but I hope it's perfect for me. The musts in my mind are quality throw out bearing and LT5 PP if not going RAM.
Ted

[efnfast]

I can't caution enough about staying away from the Ram setup.

[Paul Workman]

Originally Posted by efnfast

I can't caution enough about staying away from the Ram setup.

Oh, really!! Well, do tell. This is first I heard of any issues with it. Several of them are in service here in FBI land; all dual-disc setups, if I recall.

It would be good to get to the bottom of any issues you've encountered!

[efnfast]

Paul, I don't even know where to start.
I was told the Ram stuff would work with my new to me Fidanza. Wrong.
The shims for the release bearing wouldn't fit the input shaft.
Not enough shims were provided.
The shims would not get us to the required tolerances. Three was too little, four was too much.
The provided lines rubbed a hole in themselves on the PP. Tear it apart again and BUY 45 degree elbows from Ram.
The clutch slips.
All told, my mechanic had about 40 hours invested into the install.
That's why I'm looking for recommendations in another post.