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2G How low of a flywheel step height is too low?

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Kryndon

Proven Member
944
591
Jan 10, 2014
Bulgaria, Europe
Hey there,

Long story short, my clutch plate snapped and I got a lightly used Competition 2100 clutch+disk to put in. Upon disassembling everything, we saw that my flywheel was very rusty and had a bad surface. I wanted to have everything done right as I'm tired of clutch issues so I had the shop send the flywheel to get resurfaced and I specifically told them to aim for the 0.612" or 15.5448mm step height.

After 3 hours they called back and said they got it to about 15mm, which would mean about 0.590 inches. I asked why they had it cut so low but they said I was being too precise and they didn't see the point... Anyway I put a different clutch fork just in case, we shimmed the pivot ball with a 1G head stud washer (I believe 3mm thick) and put everything back together. Bled the system twice, adjusted clutch pedal for maximum travel, but now after break in (did a 1800 mile non-stop journey) the clutch engages almost right off the floor and when I'm feathering it the whole car shudders and feels as if my drivetrain is about to explode. I have not tried launching it yet, but I'm pretty sure something is wrong.

I should also add that we discovered many missing bolts and dowels for the engine-tranny and the mounting bolts for the T-case, so we made sure to put them in. Could this have affected how the power is transmitted and how it feels now? The engine mounts are currently stock rubber, but will be putting polys soon.

Thanks for reading, I'm sorry that it turned out this long but I wanted to get as many details in as possible!
 
I just want to put an update to this. The car has been fine so far, the shuddering/vibration went away after about 200 miles worth of daily driving. Clutch pedal feels fine and it engages normally.

However, like you and the FSM states, the acceptable range is .608-.612 for optimal performance and longevity. Doesn't mean you wont get away with a bit less like in my case. Of course this is temporary and will probably fit an aftermarket flywheel at some point in the near future.
 
.608-.612 is for a stock clutch on a stock flywheel. Remember aftermarket shit aftermarket fit. Seeing the variability in the thickness of clutch discs as new from various suppliers, I cannot believe that they have put any work into determining the ideal step height.

For example, ACT street disc is about .020" thicker than a puck disc. How in the hell can they use the same step height?

None of the clutch guys produce a product that is engineeredfor optimal clutch actuation and holding power. They engineer shit that is a giant compromise that works ok in a bunch of situations.

A proper step height should be selected after looking at the clamp load vs. deflection curve( most PP develops the greatest clamp load with the fingers above flat by .100 or so), while taking into consideration the position of the fingers, They should be slightly above flat to provide the best release action, (it should be half of the total needed release travel), however this is limited due to the centrifugal assist that the rpm provides which pulls the fingers out. (this is was causes release issues at high rpm) You also need to have clearance between the fingers and the disc, which can get really tight on some shallow step heights.

Really, for peak performance we should be adjusting the step weight as the disc wears, although that really isn't feasible.

Final note, shimming the pivot ball doesn't do shit.
 
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