89 YJ hyd clutch issue

[Kampy]

4 cyl, internal slave

My son called me last night on the way back to college, he was on the interstate and the clutch started slipping to the point the jeep quit moving. I did some over the phone t-shooting and it sounded like the clutch died.

Loaded my jeep on the trailer and headed out to swap them out, when I got there I unloaded mine and when I started his it moved and acted fine. I loaded it anyway and brought it home.

I drove it to work this morning and it was OK, tonight on the way home after about 20 miles the clutch started slipping. I babied it home and I noticed the pedal didn't have the usual soft spot up at the top of the travel, it seemed like there was alot of residual pressure in the system. When I got home it would slip on demand (throttle) I checked my hunch on the pressure and I was right, I cracked the bleeder, got a good shot of fluid out of it, closed it and checked the clutch, it's perfect again, soft at the top of the travel, hooks up about halfway through the travel. Works nice.

So my question, has anyone experienced this before, are there any known issues with these master cylinders, any other ideas? The master was not over full but the heat of operating the vehicle seems to be the contributing factor. Could a plugged vent on the cap cause this?

Thanks guys.

[NAILER341]

i have gone through a few of those masters on my wifes jeep.
check inside on the floor on the drivers side for fluid.
every time her master took a dump there was fluid on the floor and dripping down the inside firewall.

bleeding that internal slave is also a good time. i found it best to gravity bleed it.
just keep pouring it into the master until you have a steady stream of clear fluid coming out of the bleeder through a small piece of clear tubing.