Disc Brake conversion - can’t get pedal pressure

Brakes, Steering & Suspension

  1. hunt2elk

    hunt2elk FBBO Gold Member FBBO Gold Member

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    Not that it matters, but I would bet that one has a residual valve in the front chamber.
     
  2. dadsbee

    dadsbee FBBO Gold Member FBBO Gold Member

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    Quite possibly the problem. I did the on the car bleed, spent hours trying to bleed the master and ended up having to lift the rear end of the car as air was trapped in the nose of the master.
    beerestoration2018 2085.JPG
     
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    • diesel_lv

      diesel_lv FBBO Gold Member FBBO Gold Member

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      I had same problem with entirety purchased from Dr Diff. 15/16 master, rear brake cylinders etc... Cass said I needed to cut my rear brake line and install, I believe a 2lb, residual valve. This requires a flaring tool to do. I had brake shop do it. That was with a new Dr diff master cylinder and new rear brake cylinders.
       
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      • moparedtn

        moparedtn Ed on the Ridge FBBO Gold Member

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        Oh man, that looks scary!
         
      • Ironbuilt

        Ironbuilt Well-Known Member

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        Just my 2 cents, but a bench bleed is always more effective than a pedal bleed for master cylinders.
         
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        • dadsbee

          dadsbee FBBO Gold Member FBBO Gold Member

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          :drama::luvplace:
           
        • khryslerkid

          khryslerkid FBBO Gold Member FBBO Gold Member

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          Just throwing out my experience bleeding systems over the years, they suggest bench bleeding for a reason. The brake pedal won't bottom out the piston in the master cylinder like it will when doing it out of the car. If the piston wasn't bottomed out when bench bleeding there still could be air trapped. (You might have done this) Sometimes on rare occurrences air can find it's way out over a couple of days.

          The 15/16" bore master cylinder creates more pressure at the caliper and wheel cylinders than the 1" bore. The thing is you'll have a bit more pedal travel with the 15/16" bore. Maybe up to an inch more than the 1". Using a synthetic fluid like Dot 5 will create even more pedal travel. (That's why I asked what you were using).

          The way I check for a bad master cylinder (internal leakage/bypass) is to pump up the pedal till it's hard and hold the pedal firmly. As you're doing this, slightly release pressure and feel if the pedal starts creaping down. If you experience this then it could be leaking internally.

          Of course peaking under the boot at the rear of the master cylinder and inspecting it for fluid leaking is a sign of a bad one also but in this case the master cylinder could be operating properly.

          Another I have to ask...You do have the front brake line hooked to the large reservoir? (Not easy to do with most master cylinders having two different size fittings but you never know).

          The brake pedal rod needs a little play just enough that it's not applying pressure on the piston not allowing it to return to it's most rearward position. That's another thing to check.
           
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          • Ironbuilt

            Ironbuilt Well-Known Member

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            Sounds like you've done this a time or two. :poke:
             
          • moparedtn

            moparedtn Ed on the Ridge FBBO Gold Member

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            Here, let me help you with that response...
            "Although the front lifting arms aren't being used here, I only used the lift far enough to slightly raise
            the rear of the car without the rest of the car touching the lift anywhere else - or sliding off the rear
            lifting arms."
             
          • Ironbuilt

            Ironbuilt Well-Known Member

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            Mechanics do it all the time. As long as the other wheels are touching the ground, no harm, no foul.
             
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            • dadsbee

              dadsbee FBBO Gold Member FBBO Gold Member

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              ^^^, ya'd think I was stupid or something! Lifting pads are also stuck against the front leaf hangers...
               
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              • moparedtn

                moparedtn Ed on the Ridge FBBO Gold Member

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                All I said was that it LOOKED scary, hoss....
                 
              • Ironbuilt

                Ironbuilt Well-Known Member

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                "If you're scared, get a dog!!"
                 
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                • khryslerkid

                  khryslerkid FBBO Gold Member FBBO Gold Member

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                  tenor (6).gif
                   
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                  • moparedtn

                    moparedtn Ed on the Ridge FBBO Gold Member

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                    Something looking scary and actually being scared ones' self are two different things entirely...

                    One thing dying a handful of times cures a fella of is ever being scared again - of anything.
                     
                  • Ironbuilt

                    Ironbuilt Well-Known Member

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                    Sounds good...HOSS!!
                     
                  • Ironbuilt

                    Ironbuilt Well-Known Member

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                    But scared is scared. Just saying.
                     
                  • moparedtn

                    moparedtn Ed on the Ridge FBBO Gold Member

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                    Roger that, Buford. :lol:
                     
                  • 65_Satellite

                    65_Satellite Well-Known Member

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                    And would that be an issue? Here are the two ports
                    12B3F082-B186-4EFF-952A-AE9671E2E84F.jpeg 9103D393-004D-4E04-9621-F6E8E8F7C9A0.jpeg
                     
                  • 65_Satellite

                    65_Satellite Well-Known Member

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                    I agree and I usually do that but for some reason ended up mounting this and after squeezing under dash to tighten the nuts I realized I didn’t but I didn’t want to remove it at that time
                     
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