Master Cylinder Internal Arrangement Question

Brakes for your Classic Mopar

  1. I8NEMO

    I8NEMO FABO Gold Member FABO Gold Member

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    This is a RSD-DBMC10 I got from Summit. I bench bled it months ago with DOT 3, All other brake components are new and have never seen brake fluid. Now I have made the decision to go with DOT 5 and am cleaning it out. I coaxed the rear piston out with some air, careful not to eject it across the shop so I'd have orientation, laying in the bottom was the spring and a retainer apart from each other sort of stuck in what I assume is assembly "grease" which is clear/opaque (is it possible this is congealed DOT 3?, never seen anything like it) at the bottom of the bore. I have both pistons oriented correctly in the pic,at least that is how they came out, however the last (first in) spring and retainer are a guess. This retainer does not fit into the end of the spring, it's a little big for the spring opening. Need a little help here with the spring and retainer orientation fellas, could not find Right Stuff Detailing anywhere on-line.

    Thanks in advance!

    Tim

    master cylinder spring pic.jpg
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    What is the closest OEM application for that master? Should be a breakdown "in the book"
     
  3. pishta

    pishta I know I'm right....

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    I think that retainer goes behind the spring like a seat. Does it fit like that? The front one looks like that from here
     
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    • pishta

      pishta I know I'm right....

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      DOT 3 will absorb water but not to the extent of jelling. It could be packing grease.
       
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      • Murray

        Murray FABO Gold Member FABO Gold Member

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        In general you are correct, but I have never seen that white retainer before. Could it fit first on the front piston followed by the spring? In this position it would serve to expand the rubber seal and locate the spring on its small end.
         
      • CFD244

        CFD244 These pretzels are making me thirsty. FABO Gold Member

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        IMG_0116.JPG

        IMG_0117.JPG
         
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        • Oldmanmopar

          Oldmanmopar Going left turning right FABO Gold Member

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          It is a seat for the spring on the piston to prevent the spring from wearing the aluminum piston.
           
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          • I8NEMO

            I8NEMO FABO Gold Member FABO Gold Member

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            That's what I thought too, but it doesn't fit in, or around the spring, on either end. It does appear to be the same retainer as on the front piston and Im wondering if it even belongs in there at all.
             
          • pishta

            pishta I know I'm right....

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            yeah, it looks as if it goes on the spring to center it in bore and prevent contact with wall. See if it fits like that, teeth facing the front spring, first part back into the bore.
             
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            • I8NEMO

              I8NEMO FABO Gold Member FABO Gold Member

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              Not positive yet, Right Stuff was no help. Summit shows this applicable for my 68 Barracuda, but I've seen other data showing it originates post 73.
               
            • I8NEMO

              I8NEMO FABO Gold Member FABO Gold Member

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              Last edited: May 16, 2022
            • I8NEMO

              I8NEMO FABO Gold Member FABO Gold Member

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              The o.d. of the piston stem is much smaller than the i.d. of the retainer, the small end of the spring however is a great fit over the piston stem
               
            • I8NEMO

              I8NEMO FABO Gold Member FABO Gold Member

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              Executive decision after looking in service manuals etc. Even though the center hole in the retainer is larger than the piston stem this is how the books show it, like Old Man Mopar has it. I believe the cups gotta have spring tension against it or it would slide forward on each pedal return. After a closer look the teeth on the retainer never actually touch the rubber cup.
              So, it's big end of spring in first then retainer then secondary piston, then primary piston. Got it bench bled and back in the car with some make shift nipples

              20220517_153044.jpg

              20220517_085835.jpg
               
            • AJ/FormS

              AJ/FormS 68 Formua-S fastback clone 367/A833/GVod/3.55s FABO Gold Member

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              Not a Mopar, but it's the only image I could find on Google, with that lil part; you get the idea
              10994_50a9ce4699c6c.jpg
               
            • I8NEMO

              I8NEMO FABO Gold Member FABO Gold Member

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              Awesome find! Thanks for this, looks like I got it right. Funny that housing looks just like my old factory unit. Much appreciated.
               
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