I have a good ol' 1986 toyota 4runner 4x4 automatic
i noticed one day of driving that my motor was real sluggish and i couldnt take it past 50, i came to a stop and smoke billowed out of the front wheel wells...my brakes were hard as a rock
my parking brake was not engaged
..so after letting it cool down in a walmart parking lot i managed to get her home
i ruled out the master cylinder as the culprit..at first..because we replaced it a year ago
so i rebuilt the calipers and put fresh fluid in the system thinking this might fix it.

so after this was done..the same thing started happening again id let the engine warm up and put it in drive and it would be extremly sluggish and the brakes would be hard. one time i loosened the bleeder nut while the brakes were locked up and fluid SQUIRTED out and the truck was fine after that, and brakes worked fine as well..but when i shut it off and everything has cooled (overnight) and id start it up again, the FRONT brakes start to lock

and it happend again today...i had to pull over and loosen the bleeder screw (luckily i always carry a 10mm wrench in my yota lol)

so i my current conclusion on this issue is possibly one of the pistons in the master cylinder are sticking....

please let me hear what you have to say on this!!!!!

 

I had this issue with my Dodge, turned out to be the rubber brake lines were corroded from the inside, giving me a one way check valve of sorts.

 

I just had this problem. It was the master cylinder.

 

My truck has been running a little sluggish and my brake pedal feels a little more firmer than normal. I think you have just helped me with my problem. Thanks

 

Id check into the brake lines first. Definetly cheaper than replacing the MC without knowing for sure. Also, did you take the master cylinder off for some reason then it started doing that after you put it back on? cuz the little shaft that comes outa the booster can go in crooked and stick out to far and produce similar brake stickage. IF it just started doing that wouldnt be the problem though.

 

well its wierd because i replaced the alternator a week ago and i didnt have the belt adjusted right and this is when these problems with my brakes were happening and i adjusted the belt yesterday and it seemed the brake lock dissapeared?! i drove it to school and no problems...strange
i do notice if i pump the brakes before i start it and the brakes dont lock...it has me puzzed...could it be a small vacume leak?
i havent touched the master cylinder since we put it on, and the rubber lines look ok for the most part (no cracks)

and thanks to everyone who posted their wisdom on this thread!!

 

X2 on checking the master cylinder shaft.

 

well come to find out it was my brake booster that was the culprit
there was a gnarly leak right were the rod comes out of it