19874skinner

hey everybody, trying to track down the cause of my brake problems...i have gone through 2 different brand new master cylinders, every time i install a new one and go to pump my brakes to bleed them, it blows whatever seal is around the plunger and starts leaking fluid out between the master and brake booster. I thought for sure i purchased a bad master the first time it happened, however with this second occurence i am pretty confused and frustrated. my thoughts are the plunger is moving too far in and overextending it, but the rod coming out of the booster is not pushing into the plunger when i installed both parts.

i have a disc brake swap in the rear, the first master i used was for a 1987 4runner and the second master was from a fj80. the vehicle in question is a 1987 4runner.

any ideas anybody? i want to drive my truck

2ToyGuy

I am far from being an expert on brakes.
BUT: Did you adjust the pedal according to the FSM before you tried bleeding? It can make a huge difference.

Have you tried applying vacuum to the booster, through the big hose that goes to it from the TB, and seeing if it holds?

Did you bleed out the master cylinder before you tried to start bleeding the rest of the system? It can make a big difference. All it takes is some air in the plunger of the master to cause problems like this. There's a procedure in the FSM on how to bleed the master first.

Hope this is some small help...
Pat☺