Front Brakes Locking On After Car Idles.

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I had a similar problem. My front brakes would lock up after driving around for about 20 minutes. I also thought it was heat soak. I even bought a laser temp gauge to check the brake line temperature. The line temps would go up to 180 under the hood but as it turned out it was the push rod in the Master Cylinder. As long as you have some space (above the fluid level) in your MC any line pressure should be able to bleed back up into that space. When you step on the brake pedal fluid is forced out and when you release the brake some fluid flows back up to the MC. If that didn't happen your brakes would be locked up all the time. That's why MCs have a flexible rubber boot under the cap (or a small vent hole), so that pressure isn't static.
Get the front wheels off the ground, remove the MC (but leave it attached and floating), start your engine and spin the tires/wheels (by hand) every 10/15 minutes to see if it makes a difference....it won't cost a dime (except for the gasoline!!). That's how I figured it out on my car!!!:steering::thumbsup:

Treblig
 
Sounds good, we will try that. Will have to wait until ground dries up or freezes to get to car to do that. Just don't get why it happened after engine swap and now before.
 
alldodge426 said:
Sounds good, we will try that. Will have to wait until ground dries up or freezes to get to car to do that. Just don't get why it happened after engine swap and now before.
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Yes, it's strange that it happened after the engine swap. But you have to eliminate one thing at a time or you'll never get anywhere. Just make sure to block the back tires so the car doesn't roll while you have the front wheels off the ground. If the brakes still lock up after removing the MC then you know that the problem is in the lines/heat. You didn't touch any of the brake lines, MC or anything AT ALL during the engine swap???

Treblig
 
Treblig said:
Yes, it's strange that it happened after the engine swap. But you have to eliminate one thing at a time or you'll never get anywhere. Just make sure to block the back tires so the car doesn't roll while you have the front wheels off the ground. If the brakes still lock up after removing the MC then you know that the problem is in the lines/heat. You didn't touch any of the brake lines, MC or anything AT ALL during the engine swap???

Treblig
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The reason I ask is because if you disconnected the brake lines to get the engine installed and you got any air in the line, just remember that air expands at a much higher rate than fluid. Air won't bleed back into the MC. I also had to bleed and bleed and bleed my front lines to make sure that it wasn't part of my problem.

Treblig

Treblig
 
Didn't touch brake system until problem arose and changed front hoses as it was suggested that they were collapsing. Bleed system until pedal was firm and had car on stands and rotated wheels by hand and applied the brakes to see when brakes would begin to engage.
 
alldodge426 said:
Didn't touch brake system until problem arose and changed front hoses as it was suggested that they were collapsing. Bleed system until pedal was firm and had car on stands and rotated wheels by hand and applied the brakes to see when brakes would begin to engage.
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Could be as simple as the master piston spring got weaker after use not returning the piston all the way.
This could explain the change, when nothing in the brake system was altered or changed.
 
We will try jacking it up and taking m/c nuts off booster, letting it hang and letting it idle and try to rotate wheels. Will at least eliminate m/c system components from the equation. Thanks for the suggestions

alldodge426
 
Problem resolved! Moved distribution block up beside master cylinder using bracket from s10 and no more lock up. Problem was heat soak from exhaust heating block and expanding fluid. Thanks to all who made suggestions and provided ideas if things to check.
alldodge426 said:
Checked hardline-no kinks
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I always get a ton of satisfaction when I solve an annoying problem on my car!:thumbsup:

treblig
 
We got car out this spring, removed m/c from booster, jacked both front wheels off ground on stands and started car. Within fifteen minutes the front wheels started to get hard to turn without ever touching the brake pedal with car idling. Eventually wheels would not turn by hand. This led me to believe fluid was getting heated by exhaust and expanding, which led me to relocate distribution block up next to m/c. I was curious before discovering this that the m/c seemed to be leaking out the lid and m/c was new. I guess I didn't put 2+2 together. Anyway, once again to everyone who posted suggestions and maybe this post might help others who come up against this.
 
alldodge426 said:
We got car out this spring, removed m/c from booster, jacked both front wheels off ground on stands and started car. Within fifteen minutes the front wheels started to get hard to turn without ever touching the brake pedal with car idling. Eventually wheels would not turn by hand. This led me to believe fluid was getting heated by exhaust and expanding, which led me to relocate distribution block up next to m/c. I was curious before discovering this that the m/c seemed to be leaking out the lid and m/c was new. I guess I didn't put 2+2 together. Anyway, once again to everyone who posted suggestions and maybe this post might help others who come up against this.
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it's great you posted the final resolution. Often times we never hear the real answer to the question.
 
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