Bob's Component Resto Part 10: The Brake Master Cylinder

Members Restorations

  1. cruiser

    cruiser Well-Known Member

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    Good evening my fellow Moparites. I trust you've enjoyed our bedtime reading stories parts 1 through 9. Here is our latest installation to help you fall asleep this evening. Tonight we'll cover the restoration of the brake master cylinder assembly on my 1974 Gold Duster. My car came with the factory code B41 power front disc and rear drum brakes. When I purchased my 229,717 mile car in Portland OR in April of 2019, it was clear that the poor condition of the brakes would preclude me from driving the car home to Minneapolis. The pedal was very spongy and the power assist would cut out as the car came to a stop - unacceptable from a safety standpoint. So repairing the braking system became my top priority once the car came off the transporter back at my home. I started by removing the master cylinder, vacuum booster and the brackets that mounted these components to the firewall. The brackets were quite corroded, and the vacuum booster looked as bad as it worked. I also did a thorough inspection of all four wheel brakes, and was happy to learn that the individual wheel brakes were in good shape with plenty of pad and shoe life left. All calipers, hoses and wheel cylinders were in fine condition and leak free, so I concluded that the brake problems were with the master cylinder assembly. Once all was apart, I sent the master cylinder to a repair facility in Minneapolis where they tore the unit down to its bare shell, then line honed it and installed a stainless steel sleeve and new piston assembly. It was then bench tested and painted factory correct semi-gloss black. I could have saved myself a lot of trouble by simply installing a parts store replacement master cylinder, but I wanted to retain the originality of this component with all its associated markings and date codes. Note the photo of the black anodized aluminum identification tag attached to the master cylinder cover. I'm not sure what these markings mean, but I know that this tag is original to the car. While the master cylinder was out, I sent the vacuum booster to the Power Brake Booster Exchange in Portland OR. There, they tore down and rebuilt my booster, replacing all the rubber components and zinc dichromating the booster shell as the factory did in 1973. It was a bit pricey at $227.00, but they were nice enough to offer me a veteran's discount. Thanks guys! Once everything was back, I bead blasted and refinished the bracket assembly with three primer coats and three finish coats of Krylon Satin Black. I noted that the factory original finish on these brackets was a single unprimered coat of black paint. I soaked all the rusty original fasteners in Evapo-Rust, then treated them with Rust Prevention Magic to prevent any future corrosion. Next, I bench bled the master cylinder, mounted the master cylinder and booster to the brackets, then installed the refurbished unit onto the firewall with a new rubber vacuum supply line and spring clamps. I connected the front and rear brake lines, then bled and refilled the entire system with synthetic DOT-3 brake fluid. Finally, I replaced the badly faded decal on the vacuum booster with a correct reproduction decal. The number 25 on this decal refers to the last two digits of the booster part number. These decals were used by the assembly line workers to quickly identify the correct master cylinder/booster to put on a car as it came down the line, as indicated on the car's broadcast sheet. I've included a photo of the original perfectly preserved broadcast sheet that came with the car. Note that the number 25 in the "mas cyl" box matches the number on the vacuum booster decal. The test drive that followed confirmed that my brakes were now working perfectly. In fact, the car brakes remarkably well given its lightweight six engine and power boosted discs up front. And so this concludes tonight's bedtime reading for my Mopar faithful. I hope that you're nice and drowsy now, and wish you a long and comfortable nap this evening. Be kind to one another and look forward to our next installment. Night night!

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    Last edited: Oct 26, 2020
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    • 78kitcar

      78kitcar Well-Known Member

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      nice job! Booster cleaned up nice too
       
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      • FJRdoc

        FJRdoc FABO Gold Member FABO Gold Member

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        Does your Duster have a Gator grain top?
         
      • cruiser

        cruiser Well-Known Member

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        No. "Gator Grain" vinyl tops were not available on A-bodies in 1974. Mine is the "snakeskin" vinyl roof.
         
      • FJRdoc

        FJRdoc FABO Gold Member FABO Gold Member

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        Nice color combo
         
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