Hi Ruben,

I believe what you are experiencing is that the brake fluid is expanding. Under normal situations the expanding fluid would just travel up past thought the master cylinder back up to the reservoir. Something is keeping the fluid from doing this.

Is there any pulling left or right when you apply the brakes? If yes, you could have a partially internally collapsed rubber brake line. When pressure is applied, it will push past the restriction, but when you release the brake pedal, there is not enough return pressure to get past the restriction. If the car is pulling left, I would first check the right brake hose. When you experience the dragging brakes, pull over and crack open the bleeder valve momentarily on the opposite side than it is pulling. If my thinking is correct, you should get a small spurt of brake fluid and the dragging should stop for small amount of time.

If the car is not pulling when you apply the brakes, check to make sure that you have at least a 1/4″ of free play on the brake pedal. If the master cylinder piston is not coming back to the rest position, then the fluid transfer hole in the top of the master cylinder bore is being blocked by the piston, not allowing the fluid to transfer through the master back up to the reservoir.

I hope one of these will help! I always appreciate feed back on my answers! Please let me know what you find out.

Thanks,

Andy