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Master Cylinder: Reassembly

  1. Put check valve spring in drum brake outlet.
    CAUTION: Check valve in disc brake outlet will cause disc brakes to lock up.

    Put check valve on top of spring and insert tube seat in outlet against valve. Use a spare tube nut, and screw nut into outlet to bottom tube seat. Remove nut and inspect for burrs or shavings caused by installing seat.

    NOTE: Before assembly, dip all component parts in clean brake fluid. Assembling seals dry can damage them.
    CAUTION: Polishing the piston bore on aluminum master cylinders with anything abrasive is prohibited.
  2. Install new secondary cups on rear of front (secondary) piston. Place cup lips facing away from each other. Some front pistons use a cup in rear grooves and an "O" ring in second groove from rear. Place cup so lip faces forward and back of cup is against protector washer.
    NOTE: Protector washer may be permanently attached to cup.
  3. If it is necessary to disassemble rear (primary) piston for replacement of parts see "Primary Piston Assembly" illustration.
    Fig 1: General Motors Aluminum Body Master Cylinder (Exc. Citation, Omega, Phoenix & Skylark)
    G09316802Courtesy of GENERAL MOTORS COMPANY
    Fig 2: General Motors Aluminum Body Master Cylinder (Citation, Omega, Phoenix & Skylark)
    G09316803Courtesy of GENERAL MOTORS COMPANY
  4. Coat bore of cylinder and all cups with brake fluid. Place spring retainer on end of front spring. Place spring on end of front piston so that retainer is seated inside cup. Hold open end of master cylinder down. Push front spring and piston up into bore until spring seats against end of cylinder.
    Fig 3: Chrysler Corp. Aluminum Body Master Cylinder
    G09316804Courtesy of GENERAL MOTORS COMPANY
  5. Hold master cylinder with open end up. Insert rear piston assembly with spring end going in first. Install lock ring in groove, or screw and retainer if used. Push rear piston into bore. Install stop screw and "O" ring if used.
    NOTE: Stop screw is a special screw. DO NOT use any other type as a substitute.
    CAUTION: Cadillac models (exc. Seville) DO NOT use a stop screw even though a drilled and tapped hole is provided. If stop screw is installed, damage to master cylinder piston or seal will result.
  6. Install master cylinder cover and gasket. Place beaded side of gasket against master cylinder. On manual brake systems, assemble pushrod through retainer if used. Push retainer over end of master cylinder. Install a new boot over pushrod and press boot down over pushrod retainer.
    NOTE: Two types of proportioning valve assemblies are used on 1980 "X" body master cylinders. First design is a steel valve, used at start of 1980 production and is silver in color. Second design is an aluminum valve, used since late August 1979 to present, and is gold in color. DO NOT mix or interchange valves on any 1 vehicle.
    Fig 4: Proportioning Valve Identification
    G09316805Courtesy of GENERAL MOTORS COMPANY
    TIGHTENING SPECIFICATIONS

    Application Ft. Lbs.
    American Motors
      Master Cylinder-to-Firewall 30
      Master Cylinder-to-Power Unit 30
      Brake Line-to-Master Cylinder 15
    Chrysler Corp.
      Master Cylinder-to-Firewall 17
      Master Cylinder-to-Power Unit 17
      Brake Line-to-Master Cylinder 15
    Ford Motor Co.
      Master Cylinder-to-Firewall 13-25
      Master Cylinder-to-Power Unit 13-25
      Brake Line-to-Master Cylinder 10-18
    General Motors
      Master Cylinder-to-Firewall(1)(2) 25
      Master Cylinder-to-Power Unit(1)(2) 25
      Brake Line-to-Master Cylinder 13
      Pro. Valve-to-Master Cylinder 25
    (1) Torque to 13 ft. lbs. on Chevette.
    (2) Torque to 20 ft. lbs. on Cadillac.
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