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  • Master Cylinders

    My brakes feel soft.And i want a firmer pedal.I have larger than stock rear drum brakes.Should i go with a larger bore master or smaller bore master cylinder?

    I don't know what the one on my car is now,i've yet to take it apart to measure it.

  • #2

    Re: Master Cylinders

    Re: Master Cylinders

    You'll want a larger mastercylinder, which displaces more fluid.
    I suppose you are sure there's no more air inside your current system.
    www.BigBlockMopar.com

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    • #3

      Re: Master Cylinders

      Re: Master Cylinders

      I take it you have a Vega? I ran 3" x 12" station wagon brakes on the rear, with stock fronts (good pads) in mine, (427/TH400, 12 bolt, 3300lbs, high 9s), and used the stock master cylinder. Make sure they are thoroughly bled out and properly adjusted. Rear drum brake adjustment can make a huge difference in pedal feel. 8) If you've got bigger calipers in front, you may need to change the master after all though. 8)

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      • #4

        Re: Master Cylinders

        Re: Master Cylinders

        You'll want a larger mastercylinder, which displaces more fluid.
        I suppose you are sure there's no more air inside your current system.
        I bleed them like ten times through out the summer,always getting just fluid,no air.}

        The car is a 76 Vega with Monza front rotors and calibers and Chrysler 11 x 2.5 inch rear brakes.I installed the Monza master cylinder and the brakes have always worked just OK.The car is getting really hard to stop at 122+ MPH.

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        • #5

          Re: Master Cylinders

          Re: Master Cylinders

          People often forget that the master cylinder itself needs to be bled. If you don't get the air out of it; the pedal will never be hard.

          Also, making sure the rear brakes are adjusted. Many are not self adjusting. I have to adjust the rears on my Impala and Caprice about every time I change the oil. It makes a huge difference slowing the car down at 70+ mph.
          BS'er formally known as Rebeldryver

          Resident Instigator

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          • #6

            Re: Master Cylinders

            Re: Master Cylinders

            If there's any sign of brake-fading you might be able to drill some 3/8" holes in the backingplates, and even create something like a little airscoop to direct air into the brakes.
            But this shouldn't be necessary. I think there's a still problem somewhere.
            www.BigBlockMopar.com

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            • #7

              Re: Master Cylinders

              Re: Master Cylinders

              Master cylinder was bench bleed with the good bleeders with the tubes,not just the plugs they give you now.Rear brakes are adjusted alot.I abuse them pretty bad stageing the car and bringing it up on boost.

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              • #8

                Re: Master Cylinders

                Re: Master Cylinders

                If there's any sign of brake-fading you might be able to drill some 3/8" holes in the backingplates, and even create something like a little airscoop to direct air into the brakes.
                But this shouldn't be necessary. I think there's a still problem somewhere.
                No real brake fading,just a poor pedal.With all new pads and shoes i still can't get more than 1/2 a pedal to begin with.

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                • #9

                  Re: Master Cylinders

                  Re: Master Cylinders

                  there is math on the proper way to do it like in a old tech school text book (wish id kept mine) the only place that would answer my questions when we had a problem child car at work(we do alot of brake conversions) is wilwoods tech guy .always informative .peddle ratios , mc bore ,caliper bore, wheel cyl bore all determine how good/bad brakes work

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                  • #10

                    Re: Master Cylinders

                    Re: Master Cylinders

                    I'm not fimiliar with what came stock on the car, but are you sure you have a discbrake-mastercylinder in your car, as opposed to a drumbrake-MC ?

                    Also, changing from rubber flexible brakelines to braided teflon-lined brakelines will firm up a system aswell slightly. (This is not from personal experience yet, but I've heard a few people mention this)
                    www.BigBlockMopar.com

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                    • #11

                      Re: Master Cylinders

                      Re: Master Cylinders

                      If your brakes are properly bled then you probably do need a different sized master cylinder.

                      My old '69 Firebird 400 and my '77 Skylark use(d) identical Brake Pads and Shoes, but different Master cylinder, Caliper and Wheel Cylinder. I'm assuming the cars weighed about the same (F-body with heavy Pontiac V-8/700R4, vs X-body with lite Buick V-6/TH200) and the Firebird stopped a hell of a lot better than my Skylark does (especially now) using the same frictional area against the rotors and drums. I'm guessing the bore's were matched up better on the Firebird than the Skylark. Eventually I'll look them up and see what the diameters were and what will cross bolt over or the next closes thing to get the same braking out of the Skylark.

                      When working at AZ we had a customer come in and purchase a master cylinder, dismantle it to measure it out, then return it (much to our dismay) and purchase another and repeat the process so he could find the the bore size he was looking for (he didn't believe our books :-\) for an RV he had. He never found one he liked and reminded us everytime he came in.
                      Escaped on a technicality.

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                      • #12

                        Re: Master Cylinders

                        Re: Master Cylinders

                        The stock master cylinder is a 7/8th bore.
                        I'm looking at going with a Strange wich comes in a 1.125 and a 1.032,now i just need to figure out which one i need?

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                        • #13

                          Re: Master Cylinders

                          Re: Master Cylinders

                          7/8 is definitely to small!!! most of the ones that come in ssbc kits are 1.125 or1.0625 pedal ratio is important also with manual brakes i think willwod guy said 6 to one which is if distance from where where pedal swings to where MC hooks up is 2inch fromwhere MC hooks up down to center of pedal needs to be 12 inch

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                          • #14

                            Re: Master Cylinders

                            Re: Master Cylinders

                            7/8 is definitely to small!!! most of the ones that come in ssbc kits are 1.125 or1.0625 pedal ratio is important also with manual brakes i think willwod guy said 6 to one which is if distance from where where pedal swings to where MC hooks up is 2inch fromwhere MC hooks up down to center of pedal needs to be 12 inch
                            The car is an original manual brake car and i never messed with any of that,the Monza master cylinder is a direct swap.

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                            • #15

                              Re: Master Cylinders

                              Re: Master Cylinders

                              It took me several different master cylinders to get the 'Stang right after I put in the Turbo Coupe rear (rear discs). Finally someone on a forum suggested a Corvette master (I forget the year), and it did the job. It was some time ago and I don't recall the bore, and don't know if this is of any help to you, other than to let you know that others have fought this battle, too.

                              Good Luck
                              Dan

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