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Brakes that don't really "lock up"

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  • Brakes: Brakes that don't really "lock up"

    I bought the Turner disc kit and dual master for my 59 Hawk back in September of 2013.

    Installation went well, and it stops straight.

    But I saw this comment about someone with the kit "The pedal was high and had the typical 1" of travel before the brakes locked up"

    My car "oozes" to a stop pretty quickly, but my system doesn't really ever lock up any of the wheels.

    Is my proportioning valve misadjusted? Or do I have another issue?

    Or am I just used to modern power assisted brakes, and am expecting too much out of my non-power system?

    Thanks

  • #2
    Sounds like the cylinder piston is too large.
    Large piston = more volume.
    Small piston = more pressure.

    A good compromise for disc-drum (works well with disc-disc also) is a 1" master cylinder piston. No power booster is required with this setup.

    Mike

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    • #3
      Originally posted by Mike Van Veghten View Post
      Sounds like the cylinder piston is too large...A good compromise for disc-drum (works well with disc-disc also) is a 1" master cylinder piston. No power booster is required with this setup.Mike
      I bought my dual master from Jim Turner, and I think that it was indeed a 1" cylinder.

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      • #4
        The instructions that come with the kit suggest removing or perforating the screen in the M/C and possibly adding another proportioning valve "if necessary". My installation went well without any extra valve (55K). "Locking up" would be bad. Stopping smoothly is good. I'm happy with mine. Good luck.
        Dave Warren (Perry Mason by day, Perry Como by night)

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        • #5
          JMHO. but if it is Jim's complete kit I'd go back and do some more bleeding. It could just be a pocket of air somewhere.

          He's sold a ton and we know they work so I'd start there.

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          • #6
            Originally posted by warrlaw1 View Post
            The instructions that come with the kit suggest removing or perforating the screen in the M/C and possibly adding another proportioning valve "if necessary". My installation went well without any extra valve (55K). "Locking up" would be bad. Stopping smoothly is good. I'm happy with mine. Good luck.
            While "locking up" may be bad for safe and controllable stopping, braking systems should have the ability to lock up all four wheels. Anything less than the ability to lock all four wheels means that the braking system is not functioning properly - ABS aside. Lock up means that the tires are sliding on a patch of liquid rubber, so stopping distance in increased relative to optimal. However, being unable to lock up the wheels does not guarantee the shortest, i.e. optimal, stopping distance. Optimal stopping distance is achieved by the driver (or ABS) modulating brake system pressure just short of "lock up".

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            • #7
              I think SweetolBob has it right. If the pedal is spongey, there's air in the system. If it's rock hard there's a pressure release problem. If you have everything about right and jump on the pedal, in a perfect world all four wheels should lock up. I've never had a car that perfect. I've had a series of "company" cars from a huge employer that always pulled left or right, but that's an adjustment problem.
              Dave Warren (Perry Mason by day, Perry Como by night)

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              • #8
                Originally posted by pbrown View Post
                I bought my dual master from Jim Turner, and I think that it was indeed a 1" cylinder.
                Are "I think" key words ?

                Rebleading is (as stated) another good option.
                As is checking the rear brake shoe adjustment (too far away from drum).

                Mike

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                • #9
                  Originally posted by Mike Van Veghten View Post
                  Large piston = more volume.
                  Small piston = more pressure.
                  Mike
                  And
                  Large piston = short brake pedal travel.
                  Small piston = long brake pedal travel.
                  Jerry Forrester
                  Forrester's Chrome
                  Douglasville, Georgia

                  See all of Buttercup's pictures at https://imgur.com/a/tBjGzTk

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                  • #10
                    I had a set of jims brakes ive had four sets the last set never did work rite I called jim did everything changed master cyl new proportioning valve had friends look at them never did figure it out it was a very scary stop I no jims brakes work great these never did

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                    • #11
                      I see much talk of proportioning valve, as if it were a fix for several problems. Only thing it will "fix" is stop the rear end from locking up first, and does so by restricting the flow of fluid to the rear wheel cylinders, delaying braking action for the rear.

                      I have installed a couple of them during DB conversions on Studes, but wound up opening them half a turn or so at a time, till wide open (therefore non-functional). Only thing they did for me was make the pedal a little firmer and the car stop a little slower. Instead of delaying rear braking, why not speed up front braking, i.e. with larger rotors/calipers, or more aggressive pads?

                      I agree, if the brakes will not lock up there's a problem some where, but the problem probably varies. First thing I'd do would be to open the proportioning valve all the way up.
                      Last edited by JoeHall; 07-11-2014, 04:42 AM.

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                      • #12
                        No one has mentioned what port on the Master Cylinder was assigned to which circuit.
                        64 GT Hawk (K7)
                        1970 Avanti (R3)

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