Brakes Locked When M/C Heats Up

[cargeek733]

Been dealing with locked brakes for awhile now that occurs after a few miles of driving regardless if I hit the brakes or not. Once heat soaks in to the m/c and fluid, the brakes will slowly get to the point where they will not let the car move at all. To get it moving again, I have to loosen the front union on on the m/c and you can hear the brakes release.

So far, I've replaced the master cylinder, which I thought would fix the issue, I've rebuilt the front calipers, the rear calipers are new, the guide pins have been wire brushed clean, and the rubber hoses are new. Metal lines do not have any kinks and the brake fluid bleeds freely.

Is it possible that one or both of the proportional/distribution valves have gone bad?

I did find a solid thread over on the bigcoupe forum about the clevis at the back of the booster being incorrectly adjusted which would leave pressure on the booster and ultimately the m/c; I checked that and there was not an issue...I warmed up the system to have them lock and then pulled the pin from the clevis to release the brake pedal but that didn't help. Also mentioned in the thread was the possibility that the phenolic spacer within the m/c can swell slightly and bind up the rear piston shaft. Link for reference: https://bigcoupe.com/phpBB3/viewtopic.php?f=17&t=16351

Am I going in the right direction? Right now, I am likely going to return the m/c that I got from rockauto and see what happens.

[cargeek733]

Fixed the issue for anyone with a similar looking for a solution in the future: my issue was the 4 inch shaft rod that goes in the booster. It was one of either two problems with the shaft rod. There's two different styles of shafts and the one that was in there seemed to not fully seat in the booster. The other issue was that the rod wasn't actually all the way in to the booster. Put the other style shaft rod that I had in there and fully seated it in to the booster and the brakes have been good since. Fingers crossed that it stays fixed.

[Hit Man X]

Great info, thanks. My old 750iL did this, but all it required was a new booster.