Mushy brakes 4 life...

Brakes for your Classic Mopar

  1. Mopar92

    Mopar92 Well-Known Member

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    I’m at the end of what I know to do. Swapped my Duster over to a V8, 8.75, 4 speed and drove it for the first time yesterday afternoon. It runs! It drives! But it’s Flintsone braking system isn’t working.
    I think I’ve got something weird going on in the drums. Here’s what I have

    1973 Duster
    1973 A body disc
    1968 B body 8.75 / 11x2.5 drums
    New rubber lines everywhere
    New disc /drum master for this car
    New wheel cylinders
    New pads/ shoes everywhere
    Manual master cyl. Stock 4 wheel drum distribution block that came on it. This is an age old argument about this. But try to overlook that for now. I’ve done a few of these A body disc conversion and actually have good bias and pedal with the stock dist block. Anyway... that’s not causing my mush.

    We have bled and bled and bled. There is no air in the system. I’m confident of that by now. Brakes almost if not go to the floor if you brake hard. And still the stopping is weak. It’s not safe. I went maybe 1/2 mile down the road to do a shift/clutch/brake check yesterday. I turned around and came back. Once at the shop the LR drum was smoking a little. Here’s where it gets confusion. The drums are adjusted out too far to eliminate that as part of the mush. The drums drag a touch by hand. If I set the emergency brake, I have a way better pedal. Obviously cant drive it like that. So the drums are adjusted out too far.... but when I set that brake I get a better pedal.

    I hate drum brakes with a passion.
     
  2. d55dave

    d55dave Well-Known Member

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    Clearly you have come to the conclusion that the problem is related to the rear brakes, it sure sounds like they are not adjusted right. Are they assembled correctly? Small pad on the front and large on the rear? Can you post some pics of the rears with drums off?
     
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    • Mopar92

      Mopar92 Well-Known Member

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      Small shoe front/Big rear. Assembled as per the service manuals. I’ll tell you another thing. Since converting to green bearings from drdiff.... the drums locked up against the backing plates. Where the backing plate goes into the drum recess. Once I tighten the wheels I was like what happened. How did tightening the wheels lock the rear. I put 1 AN grade thick washer between the axle and drum... spaced it where it doesn’t rub. Obviously I wouldn’t drive around like that. But it’s what I had to do to get the wheels tight, adjust the drum, and bleed. Guess the green bearings set my axles in a touch. Never had that problem on any of my other 8.75 green bearing swaps. It’s an absolute wonder that drum brakes even function at all as crude as the whole design is.
       
    • Bad Sport

      Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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      Did you, before assembly put the shoe in the drum to see if it was hitting on the entire surface.

      It 'sounds' like the drum may be out of round a bit and the edges of the shoes are hitting and the center is not. Hence the better feel when you have the E brake set.
       
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      • Mopar92

        Mopar92 Well-Known Member

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        Shoe fit very well and no witness marks where it shouldn’t be. I just don’t know how much more time and hatred I want to put into these drum brakes. I’d like to try to get them to work.... but I wouldn’t mind seeing them quickly get smaller in the lake either.
         
      • Mopar92

        Mopar92 Well-Known Member

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        I’m not convinced these drums are correct for this setup. Meaning I bought a “ used but in nice shape backing plate/drum setup. These are 11x2.5 finned drums. They have a recess ring in the drum that fits around the backing plate. Which is the reason I had to temporarily put washers in there to keep the drum off the backing plate by 1/16”.
         
      • Malex

        Malex Well-Known Member

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        It seems that it's an issue of the rear brake cylinders not getting the volume of fluid that it needs. Are you sure that the rear section of the master cylinder is working right? I'm sure you bench bled it. I recall a time or 2 like that with a reman MC. Swap it out and fix. Make sure though that your shoes / drums are matched.

        Now if you were to say that you had a right stuff disc brake kit I would tell you to make sure the bleeders on the rear calipers are right at the very top. I've seen and experienced that, had to bleed those with the calipers partially installed so that the bleeders were at the top in order to get all the air out, then bolt them into place.
         
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        • 72bluNblu

          72bluNblu FABO Gold Member FABO Gold Member

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          The 11x2.5” finned rear drums shouldn’t overlap the backing plates. If yours do, you’ve got a problem. Same with the axle stand off and the green bearings, you already know that you shouldn’t have to run a washer as a spacer.

          Almost sounds like you’re running SBP axles re-drilled for BBP instead of actual BBP axles, the flange offset is different. Or Moser axles with the SBP offset and 5x4.5” pattern.
           
          Last edited: Feb 4, 2018
        • 67Dart273

          67Dart273 FABO Gold Member FABO Gold Member

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          1...I bet the shoes are not properly arc'd to the drums
          2...I bet the shoes are not adjusted tight enough
          3...I bet they need to wear in a bit
          4.. The distro block/ warning switch has nothing to do with this, except "make sure it's centered." Used to be a little tool you could buy, you unscrewed the switch, replaced it with this tool, and it kept the piston centered for bleeding
          5....Just for grins, have a helper look at the firewall area as you apply the brakes, look for movement, warping of the firewall, etc

          A drum brake system with manual master should be a "rock hard" pedal, and that is the end of that story
           
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          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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          • Mopar92

            Mopar92 Well-Known Member

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            I have never bench bled a MC in my life. Race car or street car. It never made sense to “ ok it’s perfectly bled, now empty it and put in the car and hook it up”. I’m beginning to question either wheel cylinders or that master. New Junk is common now.
             
          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            ??? You don't bleed a master and then empty it. The reason you bleed a master separately is basically like priming a pump. They will (sometimes) not "prime" on their own, partly because of the floating dual piston, against any head pressure created by the brake tubing / system
             
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            • Mopar92

              Mopar92 Well-Known Member

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              Agreed it shouldn’t have this mush. Should be granite.
              -1 shoes fit the drum radius very nice
              -2 they are adjusted so tight they smoked after 1/4 mile
              -3 Then would catch fire this tight. I can see wearing them in like this.
              -5 Ha. Can’t even build enough pressure to make it flex if I wanted.
               
            • Mopar92

              Mopar92 Well-Known Member

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              I’ve seen a few masters I’ve bought came with plastic fittings and hose to route it back up into the reservoir for bench bleeding. Then you dump it out and put it on the car? That’s a time waster. I’ve just never had trouble with masters and air. This has me running around.
               
            • Malex

              Malex Well-Known Member

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              Perhaps unbolt it from the car, throw it in the vise and bleed it. You might find your problem. You tube and internet is loaded with the procedure. Good luck.
               
            • Murray

              Murray FABO Gold Member FABO Gold Member

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              We might be overlooking something. "A" bodies with disc brakes have a proportioning valve in line, holding a bit of line pressure to the rear wheels. The absence of this valve could give the illusion of miss-adjusted rear brakes.
               
            • Malex

              Malex Well-Known Member

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              Murray could be right. Make sure you have your residual check valve in the rear section of the master cylinder.
               
            • Bad Sport

              Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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              Huh?
               
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              • Mopar92

                Mopar92 Well-Known Member

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                Sure. I hope you know the washers are simply to diagnose what’s bound up or not in line. Very much a shop fix. This is a B body rear and B body axles. Not anything A body. Your backspace advice and conversations were spot on by the way thanks for that. The drums have a recess in them that for sure goes over the backing plate where it sticks in 3/16 or whatever. Hell they may not be the correct drum for these. B body plates. Just going by what I was told. Ha. I really appreciate it guys. I think I’ve got to figure out what I’ve got going on for drums, wheel and master cylinders. They are rock auto specials with tiny little 7mm bleeder screws... which I wasn’t wild about. I don’t know if I should trust them. It’s getting harder and harder to find US made brake stuff. Unless I’m looking in the wrong place.
                 
              • Mopar92

                Mopar92 Well-Known Member

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                Well... you do all this bench bleed and then put the MC on the car with fluid and pull the plastic plugs out and let brake fluid pour everywhere while you put the hard lines on. At least this is what the directions always said. I’ve just never ever had to bench bleed a master. I’ve done pressure bleeds with a helper, mighty vac, crack bleeders and let gravity work... maybe I’ve just been that lucky but I’ve just never done it.
                 
              • adriver

                adriver Blazing Apostle

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                Disk bleed nipples on top to get air out?
                Ok.
                I'm thinking the rear symptoms may be masking a simple problem.
                I would start a square one.
                Bench bleed the master cylinder.
                Put a finger over the outlet and push the piston.
                See if it squirts air/fluid past your finger under pressure.
                Keep the finger on the outlet as the piston returns and it will suck the fluid from the reservoir to where it need to go in the master cylinder.
                Put a plug in the hole you just did loosely pump/tighten it to preserve the "prime"
                Do the same on front and rear.
                Don't pour anything out.
                Put the thing back on the car.
                You won't loose much it you do it right away.
                And then have someone help you bleed it again at the threaded connection like you would nipples.
                Loosen, pump, hold ,tighten.
                 
              • Tooljunkie

                Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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                Not out of the question, bench bleeding can be a diagnosis as well
                Pull it, drain it and then refill and bench bleed. Watch for bubbles in the fill ports. The push rod/pedal may need to be adjusted too, it may not be returning and allowing master to properly fill.
                Not questioning your workmanship,but sometimes the simple things get overlooked.
                The 59 i did brakes in were not right,ended up installing residual valves in the lines to hold pressure.
                Also, e-brake can affect proper adjustment if levers arent fully returned.
                 
              • jimjimjimmy

                jimjimjimmy lobsterman FABO Gold Member

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                think about this bench bleed and how it works for a minute you have an empty bore in the mc so it is full of air so you hook it up pour in the fluid start pumping the pedal so when and if it the bore fills full of fluid means the air needs to go someplace and that is usually pushed back thru the system until it blows out one of the bleeders that can take a lot of bleeding . when you bench bleed the air is gone out of the bore and does not get pushed back into the system .
                 
              • Mopar92

                Mopar92 Well-Known Member

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                Yeah nipples are at the top for sure. Since it was a drum car and we basically emptied the entire system I wasn’t concerned about pushing air into the system.
                 
              • Bad Sport

                Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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                @Mopar92 That ^^ is something to check if you haven't already.

                Have someone work the pedal while you watch to see if bubbles are in the MC.
                 
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