Disc Brake conversion - can’t get pedal pressure

Brakes, Steering & Suspension

  1. 65_Satellite

    65_Satellite Well-Known Member

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    These are all great points. I didn’t realize that about the brake rod not fully depressing the MC when in the car. I guess I’ll just pull it out and start over. As for the brake rod, I’m using my original from the single reservoir that came with the car simply because it has the protrusion that hits the brake switch. When the pedal is fully released, it is pretty tight and I can’t really move it. Maybe that is causing the master not to fully release? I guess I can try using the adjustable one and if that makes a difference then I’ll install an inline pressure brake switch under the hood
     
  2. hunt2elk

    hunt2elk FBBO Gold Member FBBO Gold Member

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    I really don't think it matters. You can pull it out by turning in a sheetrock screw and then pry it out. I went through this several years ago with a mc I bought from Pirate Jack's who sourced them from Wayne the Ram Man. I got to deal with him because PJ had no idea what was going on. Of course Wayne was adamant there was no problem because of how arrogant he is. After a couple days he called me back saying I was right. The whole current batch of mc's he had, it was like 200 units, had bad residual valves. He had to replace them in everything he had as well as get ahold of the people he already sold them to. After that fiasco 7 years ago, I buy all my brake stuff from Cass. I'll pay a bit more for his customer service and technical help.
    I have a sneaky suspicion that your issue is inside you master. Either it is leaking internally, or like stated above by KK, I think you didn't get all the air out by bleeding it in the car. It's that last little bit at the very end of the stroke that will get the last of the air out. Don't know if that is always possible when hooked up to your pedal assembly.
     
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    • khryslerkid

      khryslerkid FBBO Gold Member FBBO Gold Member

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      This more than likely is your problem. Good luck!
       
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      • 4mulas

        4mulas Well-Known Member

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        @diesel_lv , Did it cure your problem?
         
        Last edited: Jun 13, 2021
      • 4mulas

        4mulas Well-Known Member

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        Newer Wheel cylinders don’t have residual pressure valves built into them, they are supposed to have cup expanders though (a springs which forces the cup out against the bore of the cylinder) which are supposed to eliminate the need for the residual pressure valve on the rear circuit of a disc/drum set up using an newer style master that has no residual pressure valve built into it.
         
      • diesel_lv

        diesel_lv FBBO Gold Member FBBO Gold Member

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        No it did not. I am still battling it. More lazy than anything else in this heat. Thinking it's somehow getting air in the master cylinder. Has brake shop bleed whole system. I still have to pump brakes to get them firm, then all of a sudden I'll go to apply and they are firm at the very top. They'll stay that way awhile and then all of a sudden I have to pump them again. Totally stumped.
         
      • 4mulas

        4mulas Well-Known Member

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        Hmmm..... did your shop install a 10psi residual or 2 psi residual like you said?
         
      • diesel_lv

        diesel_lv FBBO Gold Member FBBO Gold Member

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        2 psi which was the recommended one from Cass.
         
      • bc3j

        bc3j Well-Known Member

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        FWIW Another possible cause is the master cylinder bore size is too small for system requirements. I ended up going from 15/16” to 1 1/32”.
         
      • 4mulas

        4mulas Well-Known Member

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        I just spoke with him 2 days ago and he said 2 psi is for front and 10 psi is rear. (The 2 psi valve is mostly for hot rods where the master is below the floor and the inlets of the caliper lines.) You may want to email and ask or phone and ask him again.. see the link for some facts and clarification...

        https://www.ecihotrodbrakes.com/brake_facts.html
         
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        • 4mulas

          4mulas Well-Known Member

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          15/16 isn’t too small for the system at all. Yes 15/16” has a slightly softer pedal but actually has MORE clamping force than the 1 1/32” or 1 1/16”. The larger bore masters have Less clamping force but a harder pedal.
           
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          • bc3j

            bc3j Well-Known Member

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            I think we’re talking about the same thing. I look for the master and my brake system to develop 1200psi at the front calipers. Both can do it as I’ve used both in my car. The 15/16” pedal travel to achieve it is too long for my comfort level and the pedal effort does increase when I really push on the pedal to get to 1200psi. The 1 1/32” has half the travel and slightly more effort. It’s fine for me, but pedal feel is entirely personal for each driver. Just thought this might be helpful for someone.
             
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            • diesel_lv

              diesel_lv FBBO Gold Member FBBO Gold Member

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              You are correct in the 10lb. I just went through my emails w him. So that is what is in my car. I purchased online the next day and had my brake shop install. For some reason I thought it was 2lb.
               
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              • Red63440

                Red63440 FBBO Gold Member FBBO Gold Member

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                Anyone notice anything wrong in this photo?

                 
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                • Fran Blacker

                  Fran Blacker FBBO Gold Member FBBO Gold Member

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                  Hard to bleed the brakes with wheel cylinder-s cockeyed. Wonder if he solved his problem?
                   
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                  • Red63440

                    Red63440 FBBO Gold Member FBBO Gold Member

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                    Look at the pawl for his self adjuster…was that just a temporary thing?
                     
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                    • Fran Blacker

                      Fran Blacker FBBO Gold Member FBBO Gold Member

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                      There are problems with self adjusters. but why is the BP cocked. This thread died with no resolution I guess?
                       
                    • Mike67

                      Mike67 Well-Known Member

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                      Yes residual valves are only needed when the mc is lower or at the same level as the caliper. With the mc on the fire wall there is always some "head " pressure on the lines.
                       
                    • 1STMP

                      1STMP FBBO Gold Member FBBO Gold Member

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                      Not in every case.
                      When the front pistons retract the fluid in the
                      front lines is directed back to the MC. A 2lb
                      residual check valve IS required in the front
                      circuit to keep this from occurring. A test
                      for their requirement is if you have to step
                      on the pedal twice to build pedal pressure.
                      On a 4 disc system a 2lb is required for each
                      circuit.
                      I have installed such on the brake system of
                      my truck with an incorporated proportioning
                      valve. The system works as it should.
                      20211227_151541_HDR.jpg
                       
                    • Mike67

                      Mike67 Well-Known Member

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                      Im not saying it will hurt anything and i stalled them on my wifes car hoping it would correct some issues, it didnt. Everyone's directions that I've read state that they are for a MC that is at/below the calipers. I think Stranges site mention the 2lb with drums.
                       
                      Last edited: Jan 17, 2022
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