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Master Cylinder Question

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  • Master Cylinder Question

    After reinstalling various components of my brake system, I'm in the home stretch. However, I have an issue. Everything is installed, and I went to adjust the brake pedal free travel. I installed the master cyl. piston push rod full forward on the clevis in order to have room to install the mc. After installing the mc, I went to adjust the brake pedal free play. The shop manual says freeplay should be 1/4"-3/8". You adjust this by turning the push rod on the clevis. My problem is that even with the pushrod adjusted all the way forward, (which should give me maximum free play), I have absolutely NO freeplay. In fact, the push rod is already applying a preload to the piston. It's as if the push rod is too long. It's a new rod, but it's the same length as the old one, but the old one was all the way forward too before I removed it. (brake pedal freeplay was rediculously huge before removal due to other issues with the mc.)

    I'm tempted to cut off about 1/2" of the push rod, but would that affect the full travel if the piston? Also, I should state that the system has not yet been bled. (Master cyl was bench bled.)

    I appreciate all input on what to do. Thanks, Keith

  • #2
    First, do not cut the push rod! Check the threads inside the push rod for "stuff" in other words, run a 7/16x20 bottoming tap in it and clean them up. IF then you still have the problem, cut about a 1/4" off the threaded clevis, not off the push rod. that way, you'jj NOT disturb the rounded end of the push rod.

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    • #3
      The push rod is bottomed out on the clevis, I made sure of that. I thought about cutting the push rod because I still have the old one as a spare, (or as the experimental one.) I didn't think about cutting some of the threads off the clevis. I'm guessing that the rods are easier to come by than the clevis?? The rod is definately easier to remove than the clevis. Either way, if you cut the rod, you'ld have to reprofile the cut end to match the original. Still considering my options.[B)]


      • #4
        a) do you know that the M/C is correct for that car (i.e. are you the original owner or are you sure of the match) ?

        b) if (a) above is true you shouldn't need to cut anything. You only need to modify replacement non-stock parts...


        • #5
          My guess is, BOTH the new rod AND the old rod are wrong for this application, which we know not what that is! Does this car, or did this car EVER have Power Brakes? Different Pedal and rods are used.

          All under the floor CAR M/C's '47-'60 and '53-'64 C&K are all the same, with the exception of the '63-'64 Power Disc Brake Hawks that do NOT use the residual valve.

          Nice drawing, by the way! []

          Second Generation Stude Driver,
          Proud '54 Starliner Owner


          • #6
            Check your new mc pushrod hole for a foreign body jamed in it allso a lot of autos used this mc,but with a differant depth pushrod hole.So compair the depth of the hole new to old.It is a lot easer to cut the threaded end than to reshape the round end.


            • #7
              In your shop manual, brake section, page 3, figure 4, item 10, do you remember removing this flat rubber seal? They don't just fall out, even after honing and cleaning the cylinder, and can be overlooked. Then a new one gets installed behind the original one causing this same problem.


              • #8
                Wow, a lot of good ideas. First off, It's a new master cylinder from SI-correct part number per the parts manual. The car has never had power brakes as far as I know. (Everything there says "manual brakes"). It can't be too far off, the relation of the aft end of the piston, and the large hole above it is just about the same as what the drawing here shows. i. e. there's a small gap between the reservoir and the chamber around the narrow part of the piston. I'm now tempted to just bleed the brakes and see what I have. I assume the brake lights are activated by fluid pressure? If I bleed the brakes, and they function normally, and the brake lights aren't always on, I might just live with it. I also considered tapering down the end of the push rod a little to see if it will seat farther in the end of the piston. (using prussian blue to check how far it now goes in.) Thanks for all the ideas! If y'all can think of anything else, please chime in.

                Oh by the way, the drawing was scanned from the shop manual. There IS one mistake however. It doesn't affect my problem, and I'll correct it when I get home. Can anybody spot it? Hint: My mistake, not Studebaker's.


                • #9

                  The boot is only supposed to cover the actuator rod...

                  Bob Johnstone

                  64 GT Hawk
                  55 President State Sedan
                  70 Avanti (R3)
                  64 GT Hawk (K7)
                  1970 Avanti (R3)


                  • #10
                    Drawing fixed.[B)]

                    After mulling this over for the past few days, I've come to the conclusion that StudeRich is probably right. This mc is not for use on just Studes, and the push rod is kind of a "universal" length. There just isn't any other way to adjust the length, the clevis and push rod are between two immovable points. The ONLY variable is the push rod. (Not counting cutting the clevis). I've decide to trim off about 3/8" or so off the push rod. I arrived at 3/8" because that's about how much of the clevis thread is still showing past the lock nut with the push rod bottomed out. Plus, I really don't think it would actually take that much, judging by what of the piston I can see thru the large hole in the mc. Thanks for all youse guys' input.