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Home >> GMC >> 1983 >> Forward Control 5.7 M, Automatic, 475/M40 >> Repair and Diagnosis (Single Page) >> Brakes >> Mechanical - Hydraulic >> Disc & Drum >> Overhaul >> Brake Booster - BENDIX Hydro-Boost >> Disassembly

Brake Booster - BENDIX Hydro-Boost: Disassembly

  1. Secure unit in vise (bracket end up) and use chisel to cut bracket nut that retains linkage bracket to power section. Cut nut at slot in threaded section to prevent damage to threads.
  2. Remove linkage bracket from unit. Remove pedal rod boot (if equipped), and place rod retainer shearing tool over rod. See TOOL NUMBER table proper tool number.
  3. Place a punch through pedal rod from lower side of tool and push punch on through to rest on higher side of tool. Lift up on punch to shear pedal rod retainer. Remove pedal rod.
  4. Remove remnants of rubber grommet from groove near end of pedal rod and from groove inside input rod end. With small screwdriver, pry plastic guide out of output push rod retainer.
  5. Disengage tabs of spring retainer from ledge inside opening near master cylinder mounting flange of booster. Remove retainer, piston return spring, and output rod from opening.
    Fig 1: Procedure for Removing Booster Pedal Rod
    G30364
    Fig 2: Exploded View of Bendix Hydro-Boost Assembly Components External accumulator unit shown.
    G30365
  6. Place booster cover in a soft-jawed vise and remove 5 screws retaining booster housing to cover. Remove booster assembly from vise. Hold booster over a pan and separate cover from housing.
  7. Remove large seal ring from groove in cover and discard. Remove input rod and piston assembly, spool assembly and spool spring from booster housing. If spool valve is defective, complete assembly must be replaced.
  8. Inspect power piston. If deep scratches are evident, input rod and piston must be replaced. Remove input rod seals and piston seal from piston bore. Place retaining cap tool over master cylinder stud and install nut. See Fig 3.
    Fig 3: Compressing Accumulator If deep scratches are evident replace input rod and piston.
    G30366
  9. Using a large "C" clamp, depress accumulator. Insert a punch into hole in housing and remove retaining ring with screwdriver.
  10. Slowly back off clamp until tension on accumulator is released. Remove accumulator and "O" ring. If accumulator valve is faulty, remove valve using a small diameter wire tool. See Fig 4.
    Fig 4: Removing Accumulator Valves Use a short length of wire to fabricate removal tool.
    G30367
  11. Remove the dump valve by catching the tool under the pin guide near the center of the valve. Remove the 2-function valve and seat.
  12. Remove return hose "O" ring fitting if it is leaking. Remove spool valve plug, retaining ring and "O" ring. Remove tube seats using a No. 4 screw extractor.
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