When I replaced my original clutch, two of the tangs (?), fingers (?) where broken off. You had mantioned earlier that maybe it's the pressure plate, could be. I imagine that there is some clutch dumping going on when you are racing it...Mark

 

Not a Getrag, NV4500.

 

Never clutch dump it, on the rare occasion I race from the lune I three pedal it to bring the boost up.
I do speed shift it on occasion, which are fast shifts but not slammers.
The more I think about it, pressure plate issues don't seem to fit the symptomology. It doesn't slip at all (except a little under full boost speed shifts after the clutch gets hot)

My clutch is a LUK Gold unit, diaphragm pressure plate. Maybe the diaphragm spring is just worn out. It has several hundred thousand miles on it, over 2k anyway.

Probably time for a new clutch?

 

By the way, did you notice I moved the slave mount to the other side of the mount to get the most stroke possible? I though it was a good trick, but it only helped slightly. It is a sealed hydraulic unit to I disassembled the slave without breaking the seal, put it through the mount hole, the reassembled the mount plate on the other side. I think I will always do this from now on just to make sure I get the longest service life and best effort from my clutch hydraulics!

 

 

At least time for disassembly and inspection....Mark Edit: as posted above, the fork is gouging out ruts in the steel, if you didn't file them out yourself.There may be a possibility of bent release fork. Maybe you have too much throw from the modification on the slave cylinder...

 

On a side note, about 6 or 7 years ago, I was on my way to Mexico and when I got off the freeway, I had no clutch. I used the starter to get me off the road, pulling a boat. The slave had blown out the front cap, but all the pieces were there. Long story short, I JB welded the cap back on, after stuffing the guts back in, used my foot to bleed it, and drove on down to Mexico. When I got home, I bought a new slave cylinder from Rock Auto and intended to fix it. Weeeeeeell, I am still driving on that repair, with everything that I need to fix it in my tool box. Nothing like the quality of original parts...Mark

 

pedal fully depressed is a hair over an inch of throw at release arm at slave contact.

 

Update:
While I had the dash out for the heater core job, I was able to properly weld up the top part of my clutch support webbing.
Now I have full extension when the truck is cold, and when warm enough disengage not to grind.
Still don't know why it changes after 4 minutes of run time, but at least I can drive it properly.