weird brake symptoms

[Sparky]

My truck likes to mysteriously pull to both the left and the right when I hit the brakes. It can switch which direction it pulls between stoplights. So far the master cylinder, flexible brake lines, roters and pads are all new, and I rebuilt the callipers. I dont think it has anything to do with the back brakes because when I hit the e-brake it stops strait. For some reason it always gets better for a month or so after I work on the brakes,(i.e. when i rebuilt the callipers or replaced the brake lines or put on new roters and pads) and then comes back again.

Here are the thoughts I had...

1. contaminated brake fluid keeps makeing the callipers hang up

2. faulty proportioning valve

3. some combination of the two

Has anyone ever heard of a proportioning valve doing this? How can I get all contaminated fluid out? I have bled the brakes so many times since this started I am sure I have cycled multiple quarts of brake fluid through the system, and it has always been DOT3, but from different brands. What else would cause this on my 78 blazer? Keep in mind I have checked all the simple things like tire pressure.

Thanks

Sparky

When all else fails... Check the blinker fluid.
78 K-5

 

[K10ANDYKHAMNIC]

my k10 did the same thing , my prob was the steel line was crimped on one side in the back, but ucouldnt see it cuz it was covered by the stone shield springy thing . it could also be that there is still air in the lines ...

WHATS WRONG WITH A 305 ?
81 K10 GOODYEAR 35" MTRS
TH350 NP 208
STEPHENS OLD AXLES
NO BREAKAGE

 

[eastk5]

I had pretty much the same symtoms as you. Last week i changed both rear wheel cylinders, brake shoes and adjusters. Now when i slam on the brakes it actually goes in a straight line. lol

 

[Sparky]

Thanks guys. The part that baffels me is why it changes directions on me. Usually when I first start driving it, it brakes strait as an arrow. Then once it starts warming up it pulls to the left the right and sometimes both. It pulls way to hard for it to be the back brakes, and when i hit the brakes really hard I can feel one of the front tires lock up and the other one doesnt. Can anyone else offer any insight?


Sparky

When all else fails... Check the blinker fluid.
78 K-5