clutch engagement changes, then slips!!

[thecayub]

I have a problem that occurs fairly frequently, depending how long my truck is running and how much I slip the clutch. My ride is sort of unique- a 2000 tundra 4.7L that i rigged a toyota supra transmission (5spd manual) to fit. I recently installed an ACT heavy duty pressure plate and 6 puck sprung disc to handle the torque of my straight piped 4.7l. (the oem exedy clutch for the supra that I installed would slip around my torque peak). I have a wilwood 3/4" master cylinder, braided lines, and a hydraulic throwout bearing as my clutch setup. Everything has only 10,000 miles on it. Also, I have bled and bled and bled and bled the entire system in various ways.. that's definetely not the problem. Here's the problem:

when the truck is cold, the engagement point of the clutch is very near the floor, making it difficult to shift sometimes. Once the truck gets to operating temps, the clutch seems to engage in a normal position (1/2-3/4 of the way from the floor). However, as I continue to drive, or do a few hard launches, the engagement of the clutch is at the VERY END of the pedal. As you then continue to drive more, or do anymore hard launches, the clutch begins to slip. (almost like i am partly depressing the pedal) Then, if I let the truck sit for several hours, it engages in a normal position again.. I have no Idea what's wrong. Clutch experts please help! Thanks

[5 Speed]

One of the issues with installing a new clutch is letting the system drain out from the master cylinder and the slave cylinder. Did you bench bleed your master cylinder? I know you said you have bleed the system to death but maybe you damaged the master cylinder? Have you tried vacuum bleeding the system vs. the old up and down with the peddle? It sure sounds like you have air in your system and as it heats up the air is expanding. CAn you pump the system when cold and get a different engagement point? Just my thoughts.

[thecayub]

I did vacuum bleed it with an actual vacuum bleeder. I purchased if just because I had the same thoughts you stated, the air is expanding. However, I just don't think it's air in the system. How could I have damaged the master cylinder? And whenever its cold, I've tried pumping the pedal and it doesnt change the engagement point whatsoever. Thanks for your help!

[5 Speed]

I believe you can damage a master cylinder if you actually depress the plunger farther than normal pedal movement will move it. This is why when bleeding brakes it is not a good idea to actually depress the peddle all the way to the floor because it normally won't move that far. This is why I asked about bench bleeding where you can force the plunger much farther than it should move when in normal use. I don't know anything about the hydro throw out bearing but is there a preload setting on it? If you pump the clutch when cold will it release closer to the middle vs. the end of the movement? What happens if you just depress it and hold it down? Will it creep?

[silet]

Did you bleed the slave cylinder? It could also be a bad slave cylinder.

[thecayub]

Well, I didn't know that about damaging the master cyl.. maybe that's the problem. If i pump it when it's cold it doesnt change where it engages at all. Also, if i hold the pedal down it does not creep, so I know there are no leaks. I also don't lose any fluid.

@silet- I'm not using a slave cyl/clutch fork combo. It's an internal hydraulic throwout bearing with a pressurized line (from master cyl) into it and a bleed line coming out. So when you pull (vacuum) the fluid from the bleed it pulls it through the bleed line, through the throwout bearing, and then through the pressure line to the master cyl.

Here's a pic of my setup- xuzfe t56 adaptor

[silet]

That is cool!!! One less piece to worry about!!! Are you using a separate master cylinder from the brakes? I've actually seen a brake/clutch master cylinder used in a KIA. The manual Tundra uses a separate master from the brakes.

[thecayub]

Yeah, they are seperate.