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Thread: Brake diagnosis help.

  1. #11
    Registered Member Devryn's Avatar
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    Thank you! To do the adjustment, do I need to pull the pin out of the master cylinder for the rod measurement with the tool? I apologize, I'm just clueless with brakes.

  2. #12
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    do I need to pull the pin out of the master cylinder for the rod measurement with the tool?
    Depends on what your tool looks like, but probably not.

  3. #13
    Registered Member Old Buzzard's Avatar
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    Before you start adjusting anything, post a pic of the end of the master cyl, and the booster. Measure the diameter of the m/c bore.
    You have to check the free play on the pedal push rod and the booster, before you assume the booster pin needs adjusted.
    Last edited by Old Buzzard; 07-06-2021 at 04:10 AM.
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  4. #14
    Registered Member Devryn's Avatar
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    Quote Originally Posted by Old Buzzard View Post
    Before you start adjusting anything, post a pic of the end of the master cyl, and the booster. Measure the diameter of the m/c bore.
    You have to check the free play on the pedal push rod and the booster, before you assume the booster pin needs adjusted.
    Thanks sir. I've posted some pics below. Again, I apologize for my ignorance, but how do you check the free play on the pedal push rod and booster? Up under the dash?

    Specs I found online show a 1" bore size, but the measurements I took inside and outside with the caliper are somewhat different. Those pics are also below.
    20210706_122540.jpg
    20210706_111804.jpg
    20210706_111925.jpg
    20210706_111716.jpg
    20210706_111707.jpg

  5. #15
    Registered Member Devryn's Avatar
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  6. #16
    Registered Member Custer55's Avatar
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    You would adjust the pedal to booster free play under the dash. No need to measure like you do where the master cylinder mounts to the booster. Just pull the clevis pin where the booster rod attaches to the brake pedal. With brake pedal lightly resting against the return bumper the booster rod clevis hole should line up where you can easily insert the clevis pin without having to pull back or push forward on the brake pedal. This will give you just a bit of free play.
    Not sure how that tool you printed works. I just use a straight edge and a caliper to measure the depth of the booster pin and master cylinder piston from the mounting surfaces and just do the math to make sure there is a bit of clearance vs an interference fit. I shoot for about a 1/32" or so. Most of the time it doesn't need to be adjusted at all but I did need to make a slight adjustment on my son's 59 Mercury or it would have been an interference fit. This was with a Speedway 8" booster and a Wilwood 1" dual master cylinder.

  7. #17
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    The master cylinder bore diameter is the bore size of the end of the master cylinder just behind the snap ring in the next to last photo.

    Because you are measuring the interaction between the booster pin which has a spherical or ball end, and the seat in the master cylinder which is a cone, that "tool" may or may not work. The end of the tool that goes into the cone needs to have a spherical profile like the booster pin. And the end of the tool that goes on the pin needs to have the conical shape of the master cylinder's interface. Any other way of measuring needs to account for these shapes too.

  8. #18
    Registered Member Devryn's Avatar
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    Quote Originally Posted by Rick_L View Post
    The master cylinder bore diameter is the bore size of the end of the master cylinder just behind the snap ring in the next to last photo.

    Because you are measuring the interaction between the booster pin which has a spherical or ball end, and the seat in the master cylinder which is a cone, that "tool" may or may not work. The end of the tool that goes into the cone needs to have a spherical profile like the booster pin. And the end of the tool that goes on the pin needs to have the conical shape of the master cylinder's interface. Any other way of measuring needs to account for these shapes too.
    The end that goes into the MC is rounded. Now the issue is that I don't think the booster rod has any more inward adjustment left. The tool is showing that the booster rod is just a bit too long. Here's a close up of the rod...looks all the way in to me? I tried grabbing the collar nut deal with pliers and turning the end nut, but they just move together and there is no gap between the end and that collar. https://drive.google.com/file/d/1JSd...ew?usp=sharing

    Another question: Since I don't seem to have anymore inward adjustment, is there an issue with putting washers on the bolts between the MC and Booster to pull the booster out a little?
    Last edited by Devryn; 07-07-2021 at 01:14 PM.

  9. #19
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    That would be a good diagnostic check. But it won't fix your problem of weak brakes when cold. Personally I would ditch all that chrome stuff and get an 8" double diaphragm booster and a 1-1/8" bore master cylinder.

  10. #20
    Registered Member Devryn's Avatar
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    Quote Originally Posted by Rick_L View Post
    That would be a good diagnostic check. But it won't fix your problem of weak brakes when cold. Personally I would ditch all that chrome stuff and get an 8" double diaphragm booster and a 1-1/8" bore master cylinder.
    Do you have any specific brands or part numbers you'd recommend? I really don't care if it's chrome or not. Just want it to work.

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