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Thread: Brake diagnosis help.

  1. #1
    Registered Member Devryn's Avatar
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    Brake diagnosis help.

    My car has some sort if 4 wheel disk brake kit. What would cause the brakes to barely work when cold, and drag when hot?
    Last edited by Devryn; 07-03-2021 at 01:09 PM.

  2. #2
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    you always have "drag" on disc`s, but i don`t know, sounds strange.

  3. #3
    Registered Member Devryn's Avatar
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    They're heating up and you can smell it.

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    Need more info. Do you have a power brake booster? What master cylinder? Do you have a proportioning valve?

    My initial off the wall suspicion is that you have the master cylinder preloaded. This can provide both your symptoms. Preload prevents full bleeding of the system, which could be your weak brakes. When the system warms up, then the preload causes brake drag.

    Come back with the answers to the questions and maybe it can be narrowed down.

  5. #5
    Registered Member Devryn's Avatar
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    Quote Originally Posted by Rick_L View Post
    Need more info. Do you have a power brake booster? What master cylinder? Do you have a proportioning valve?

    My initial off the wall suspicion is that you have the master cylinder preloaded. This can provide both your symptoms. Preload prevents full bleeding of the system, which could be your weak brakes. When the system warms up, then the preload causes brake drag.

    Come back with the answers to the questions and maybe it can be narrowed down.
    Thanks, Rick. I wish I knew more about brakes, but I can identify parts. Looks like this master cylinder with a booster behind it https://www.summitracing.com/parts/clp-m-c118sac and it does have a proportioning valve.

  6. #6
    Registered Member Old Buzzard's Avatar
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    Quote Originally Posted by Devryn View Post
    Thanks, Rick. I wish I knew more about brakes, but I can identify parts. Looks like this master cylinder with a booster behind it https://www.summitracing.com/parts/clp-m-c118sac and it does have a proportioning valve.
    That's a start.
    We had 2 of those.
    1 leaked @ the ft port.
    1 would not bleed.
    Both went back to summit.
    We use the Wilwood units w/ adj prop valves.
    Injector inspector
    Walmart hottie stalker.
    USAF 60-64.
    The guys that brought you the Cuban missile crisis in living color!

  7. #7
    Registered Member Devryn's Avatar
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    Well...3d printed the tool for adjusting the push rod from the master cylinder to the brake booster. Took the master cylinder off and there's a rubber boot between the two and it's totally crunched, pinched, creased and split...

  8. #8
    Registered Member Devryn's Avatar
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  9. #9
    Registered Member Devryn's Avatar
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    Would the boot cause the issue I'm having?

  10. #10
    Registered Member Custer55's Avatar
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    There should not be a boot between the master and brake booster as there is no room for it as your crumpled up one shows. Get the adjustment between the master cylinder and booster correct and see what it does. There should be just a bit of clearance between the booster push rod and the master cylinder when everything is at rest.

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