I have a 1986 Toyota 4runner and my brakes are locking up. At first we thought it was just something in the lines so I bled them. That fixed it for about a week. Then they locked up again. Mainly the driver side, so I replaced the caliper on that side. Worked for another week then locked up again. So I replaced the soft lines connected to the caliper. Which did nothing. Now they lock up around every 10-15 miles I drive. So I pull over and bleed them and they're good for another 10-15 miles. Any help would be greatly appreciated

 

When you say "they lock up every 10-15 miles", do you mean on their own, with a lighter than normal apply, etc.?

How exactly are they locking up and describe what you mean - instant lock with skid, slight drag with eventual lock up...

Can you smell the brakes?

Before it locks up, do the brakes feel and work normally?

Has anyone messed with the booster / master recently?

 

It slowly drags with eventual lock up. Every time the brakes are applied the peddle slowly gets stiffer and stiffer until it eventually will not go down at all


I can smell brakes if I don't pull over immediately and bleed them.

I have had the truck for a little over a year now and nobody has touched the booster or the master since I have owned it. Before that I am not sure.

 

Normally this is from a booster/master swap where the booster pushrod length is too long. It does not allow the m/c piston to return to its zero position and blocks the fluid return port.

When you bleed the dragging caliper, I'm guessing that some fluid comes out (brakes have pressure even though no one is pushing the pedal).

Its a quick and easy check, but next time the brakes drag and you pull over, loosen the m/c nuts a little. This will function the same as lengthening the pushrod. If the wheel spins, somehow the pushrod length has changed.

 

That sounded really good, tried it two times once when caliper was just dragging once when 100% locked up. Didn't work either time

 

i am having the same problem with my 87 4runner, it drives fine for about 10 or 15 min then the truck slowly starts applying the brakes, then it takes all the truck has to get it to move at all . i replaced the master and booster but thats hasnt helped, any help would really be appriciated