Brake Pedal STILL Sinks..

Brakes, Steering & Suspension

  1. miller

    miller Well-Known Member

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    Thanks for the pics, Ron. I could be flat wrong, but that master does not look right, for a disc/drum set-up. Take a look at the master, in this post...
    https://www.forbbodiesonly.com/moparforum/threads/best-dual-master-for-m-w-manifolds.177474/

    Pretty much every master I've seen for disc/drum, has one pot larger, for the disc, the smaller for drums. Disc brakes use more amount of fluid, to move the pistons.

    The master you have, don't know anything about. (Doesn't mean much, lol!)

    On my 64, I did the old school conversion, though the car originally had power brakes, I changed mine to manual disc/drum. The same type master, shown in that post, is what was recommended, and what I used.
    Went to Napa, and bought a new Bendix master. Checked on the first Mopar year disc/drum was used, 67 Coronet RT, if I remember right. There's two different ones, one for manual brakes, one for power brakes. Both are four stud mount. (Was told the studs were hard to find, so I used collars, to make my 64 studs work.)
     
  2. RJRENTON

    RJRENTON FBBO Gold Member FBBO Gold Member

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    I believe the correct master cylinder for a disc / drum application has a significantly larger reservoir that supplies fluid to the front calipers. Usually, this reservoir section has 2x to 3x the volume as section thst feeds the rear wheel cylinders. The piston bore of the master cylinder when used with a vacuum booster assembly on a disc/drum system is USUALLY 15/16" diameter along with a proportional valve to insure even brake pressure bias front to rear to prevent rear wheel lock up during hard braking effort. Just my opinion of course.
    Bob Renton
     
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    • Ron H

      Ron H FBBO Gold Member FBBO Gold Member

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      Thank you gents - I had a fleeting thought about this MC fit seeing some setups as you describe and didn't know enough to follow this up thinking it wasn't an issue. What you're saying makes perfect sense so will follow this trail - greatly appreciate your insight as you know more than I do!
       
    • 3sloppydogs

      3sloppydogs Member

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      I seem to remember something about check valves in master cylinders. They were there to maintain a residual pressure. Can't remember if disc systems had them or just drums. Might be worth looking into
       
    • miller

      miller Well-Known Member

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      Same here.
      Besides the bore size difference, the valves in the bore can be different. Not like I knew all about it, but the various masters I've rebuilt, took the correct valves to work right.

      Good luck on it, Ron H! Gotta have good stoppers!!
       
    • Ron H

      Ron H FBBO Gold Member FBBO Gold Member

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      Will let ya know how this goes...thanks!
       
    • MarPar

      MarPar If it weighs, it pays FBBO Gold Member

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      I believe that disc brakes are the ones with a residual/check valve (either in the MC or a separate remote one like in early 70's C-bodies).
       
    • Ron H

      Ron H FBBO Gold Member FBBO Gold Member

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      I re-contacted SSBC a bit ago about their kit asking about the MC setup - I hope they might be a little more helpful than what they had been before now with my new found information here on the MC. Thanks.
       
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      • miller

        miller Well-Known Member

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        I cannot say, one way or the other, if any of the 'new and improved' master designs will work on what. It works, or it don't, is the way I look at it.
        As mentioned by most, disc/drum masters, big pot goes to the disc. Simply because the discs use a bigger piston, that takes more volume of fluid to move it. Drums take less.
        And, it's the deal of application of how the brakes get applied, with the needed valves, to make them come into play. Can be a complicated mess. Doesn't need to be, if the right parts are used.

        Mine is simple, effective, and works.
         
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        • Ron H

          Ron H FBBO Gold Member FBBO Gold Member

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          Been away from it for decades; but I used to have a better understanding of 'hydraulics' having been through training on sprinkler system design and then having to survey those systems for property insurance rating...flow rates, pipe sizing, heads, etc etc...so reckon there's a method behind the design of the reservoir bowl size/capacities, valves for the system it serves...so will be on the hunt to investigate this deal next..
           
        • Ron H

          Ron H FBBO Gold Member FBBO Gold Member

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          Got to ask yaz a question about the master cylinder reservoir size as I got some pushback on this not being an issue. Could be those tossing it back to me are not as informed as you are. Ok, it's being said that the MC reservoir size shouldn't matter it will simply use less fluid from the bowl and not effect anything if the prop valve is set correctly which seems fine with the braking action I have. Anyway, do you know why/how a larger MC reservoir would impact the drum brakes?
           
        • 69L48Z27

          69L48Z27 FBBO Gold Member FBBO Gold Member

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          That MC in your kit is just a GM MC. Looks like one from late 60’s into 70’s disk/drum. The reservoir size for this part of your project does not matter. Larger capacity is needed as the pads wear and the piston is further out in the caliper.

          Did you fix or figure out why your pedal is not returning?

          Did you pull the MC and bench bleed it?
           
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          • miller

            miller Well-Known Member

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            First...your automobile, is NOT a GM. Don't know that much about 'em, don't wanna know! I'll guess the differences between the chosen brake systems they used.

            The Mopar engineers picked 'their' poison, what brake systems they figured would work best. And, like you said Ron H, overall looking at it, it makes sense.

            When I set mine up, I looked over the later Mopar disc/drum set-ups. All the various added valves, and the like, past simply the master itself. Some of it, to me, was garbage, not needed...at least on my hot rod.
            Figured out what was needed, keep it simple, and go. The master that would work, distribution block that goes with it, adjustable prop valve to the rear drums.

            Most of the factory added valves, and like, were safety features in case the brakes failed.

            But, don't listen to me! No, not any sort of an expert. Again, it either works, or it don't. I ain't gonna jack around with my life, or anyone else's.
             
          • Ron H

            Ron H FBBO Gold Member FBBO Gold Member

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            Have a long list of fixes I tried, some of which worked with the setup as there were other problems too. As I got further along I started asking myself somethin just ain't right systemically with the whole thing then came the tips on the MC. No doubt this MC isn't correct for my front disks and rear drum system. The 'kit' from SSBC says "Mopar" A156-1-3. So they used GM masters. My later question then after getting this info was well...so I have a larger reservoir for the drums; but if it's propped right I just got a rear supply tank in the MC that's bigger than it needs to be. I held off bench bleeding this one thinking of getting an MC that's officially proper. In any case I'll bleed the one I have or get another MC. All along the brakes have worked good just the friggin pedal sink down that won't return but still can push it further down getting brakes. My next thing sifting through brake articles is possibility of the pedal setup, how I hung it and such and will look at this too. Appreciate all the advice you guys have taken time to give me.
             
          • 69L48Z27

            69L48Z27 FBBO Gold Member FBBO Gold Member

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            Also, just as a note. Whether it’s a Mopar or a GM car, the pedal on a booster car sits lower than a manual brake car. Pedal sits lower for sure. My 67 R/T looks like the pedal is on the floor compared to a manual brake B Body I had. Not sure what the SSBC setup looks like from the booster to the pedal but a stock setup uses two lever points to get the right ratio.

            I think if SSBC sells these kits for Mopars you can get it to work.
             
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            • miller

              miller Well-Known Member

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              Is that the way the brake lines are plumbed?? Believe that's wrong. Even in the master you have, if there's two sizes of pots, larger one goes to the disc brakes.
              Can't go by where the larger pot is, in the master. Mine is on the backside, but feeds the front disc.

              Drum brakes use less fluid, from disc brakes. That's the whole idea behind a master having two different sizes of pots. Drum all around have same size pots. Main reason they started using separate pots for drums all around, if rear brakes failed, you'd still have the fronts.
               
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              • RJRENTON

                RJRENTON FBBO Gold Member FBBO Gold Member

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                Ron H,
                Out of curiosity, when you were contemplating revising, up grading your original braking system, what was the determining factor that solidified your decision? Cost, availability, "ease" of installation or word of mouth recommendation by someone lacking fundamental knowledge of a hydraulic brake system?
                If you are installing on a Mopar vehicle, why would consider using GM components? Mopar used a vatiety of suppliers: Midland-Ross, Bendix being the most prominent. There is a fundamental requirement that must be taken into account. Master cylinder bore size, in relation to both caliper piston size and drum brake wheel cylinder, master cylinder stroke volume (relating to caliper and wheel cylinder required volume) to be able to supply the correct brake (hydraulic) pressure to be able to effect a safe reliable stop. Nothing against SSBC, but their main concern is $$$ for their company. They will likely recommend something that they have in stock. Perhaps you should consider beginning from zero and use a Mopar based supplier, of YOUR choosing not your buddy's. Do your own due diligence. Just my opinion of course.
                Bob Renton
                 
              • Ron H

                Ron H FBBO Gold Member FBBO Gold Member

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                A long story Bob - to sum it up some I didn't investigate this much as I should have; another example of "if I'd known then what I know now..". The time I've spent trying to rework this could have installed a dozen brake conversions!
                 
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                • RJRENTON

                  RJRENTON FBBO Gold Member FBBO Gold Member

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                  Ron,
                  There must be at least a half dozen questions I would have asked a potential supplier b4 purchasing. Cost was usually #5 on the list. When i worked in industry, I interviewed many suppliers that could supply my requirements. After listening to a plethora of claims, my answer was: "I do not give a damn what you are selling....this is what I'm buying and the price I'm willing to pay for it"..... The old expression CAVIET EMPTOR definitely applies.
                  Bob Renton
                   
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