Isuzu Cars and Trucks 1981-1991

Master Cylinder

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REMOVAL AND INSTALLATION
  1. Disconnect reservoir fluid level indicator connector at the master cylinder.
  2.  
  3. Remove all brake lines from master cylinder using a flare nut wrench.
  4.  


NOTE
Brake fluid is highly corrosive to paint. Take care not to spill brake fluid on any painted surface of vehicle.

  1. Remove the master cylinder by pulling straight out.
  2.  
  3. Installation is the reverse of removal. Tighten master cylinder to power booster bolts to 7 and 1912 ft. lbs. torque. Tighten brake line fittings to 6 and 1911 ft. lbs. torque.
  4.  
  5. Bleed master cylinder and brakes.
  6.  

OVERHAUL
RWD I-Mark
  1. Pour brake fluid out of the reservoir.
  2.  
  3. Disconnect the front and rear rubber hoses from the master cylinder and separate the fluid reservoir.
  4.  
  5. Place the master cylinder in a soft jawed vice and remove the pipe connector, check valve, spring and retainer.
  6.  
  7. Push IN on the primary piston with an appropriate tool and remove the secondary piston stop bolt and gasket. Maintain pressure and remove snapring.
  8.  


NOTE
DO NOT remove the spring from the piston.

  1. Remove the primary and secondary piston assembly from the master cylinder.
  2.  
  3. Clean all parts with DOT-3 brake fluid and dry with compressed air.
  4.  
  5. Measure master cylinder bore diameter. Specification for bore diameter is 22.22mm (0.875in.). Replace master cylinder if not within specification.
  6.  
  7. Measure primary and secondary piston outside diameter. Subtract the piston outside diameter from the master cylinder bore diameter to obtain the clearance. Specifications call for 0.0250.127mm (0.0010.005in.) with a maximum service limit of 0.15mm (0.006in.). If the clearance is larger, replace the master cylinder.
  8.  
  9. Check the master cylinder inner wall for wear, rust or damage. Check the pistons for wear or damage. Replace pistons if any wear is evident.
  10.  
  11. Inspect check valve for poor contact. Replace as necessary.
  12.  
  13. Check return port for obstructions and clean with wire. Blow away foreign matter with compressed air.
  14.  
  15. Inspect brake fluid reservoir and rubber hoses for cracking or damage. Inspect gaskets and snaprings for fatigue or damage. Replace as necessary.
  16.  



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Fig. Installing secondary piston stop bolt



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Fig. RWD I-Mark master cylinder

To assemble:

  1. Inspect parts carefully for foreign matter and lubricate with clean brake fluid. Lubricate the cylinder bore with clean rubber grease.
  2.  
  3. Clamp the cylinder into a soft jawed vice. Install the spring, check valve and gasket. Install the pipe connector hand tight. Torque pipe connector to 47 ft. lbs.
  4.  
  5. Install the primary and secondary piston assemblies. Push the piston in with an appropriate tool and install the snapring.
  6.  


NOTE
Be careful not to scratch the piston cups when installing the piston assemblies.

  1. Maintain pressure on the piston an install the stopper bolt and gasket hand tight. Torque stopper bolt to 14 ft. lbs.
  2.  
  3. Install the front and rear rubber hoses on the master cylinder. Install the fluid reservoir.
  4.  
  5. Apply rubber grease to the entrance of the cylinder housing.
  6.  
  7. Press the piston all the way into the cylinder and release several times. Check for smooth piston return and brake fluid being forced from the front and rear outlets.
  8.  
  9. Fill the reservoir with fluid and bleed the master cylinder.
  10.  
  11. After installation, bleed brake system.
  12.  

All Except RWD I-Mark
  1. Pour brake fluid out of the reservoir.
  2.  
  3. Remove the dust seal, if equipped.
  4.  
  5. Remove the reservoir attaching screw, reservoir and grommets.
  6.  
  7. Place the master cylinder in a soft jawed vise and remove the proportioning valve assemblies, if equipped.
  8.  
  9. Push IN on the primary piston with an appropriate tool and remove the secondary piston stop bolt and gasket. Maintain pressure and remove snapring.
  10.  


NOTE
DO NOT remove the spring from the piston.

  1. Remove the primary and secondary piston assembly from the master cylinder.
  2.  
  3. Clean all parts with DOT-3 brake fluid and dry with compressed air.
  4.  
  5. Measure master cylinder bore diameter. Specification for bore diameter for all vehicles except P'up/Amigo is 22.22mm (0.875in.). Specification for P'up/Amigo with 2.3L engine is 23.85mm (0.938in.); 2.6L engine is 25.5mm (1.000in.). Replace master cylinder if not within specification.
  6.  
  7. Measure primary and secondary piston outside diameter. Subtract the piston outside diameter from the master cylinder bore diameter to obtain the clearance. Specifications call for 0.0250.127mm (0.0010.005in.) with a maximum service limit of 0.15mm (0.006in.). If the clearance is larger, replace the master cylinder.
  8.  
  9. Check the master cylinder inner wall for wear, rust or damage. Check the pistons for wear or damage. Replace pistons if any wear is evident.
  10.  
  11. Check return port for obstructions and clean with wire. Blow away foreign matter with compressed air.
  12.  
  13. Inspect brake fluid reservoir and grommets (rubber hoses) for cracking or damage. Inspect gaskets and snaprings for fatigue or damage. Replace as necessary.
  14.  



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Fig. Impulse/Stylus brake master cylinder



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Fig. Removing the stopper bolt



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Fig. Removing the snapring



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Fig. Removing the proportioning valve



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Fig. FWD I-Mark master cylinder



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Fig. Truck master cylinder



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Fig. Measuring the master cylinder core with a dial bore gauge. Measure the bore at 3 positions: (A) top, (B) middle, and (C) bottom

To assemble:

  1. Inspect parts carefully for foreign matter and lubricate with clean brake fluid. Lubricate the cylinder bore with clean rubber grease.
  2.  
  3. Install the primary and secondary piston assemblies. Push the piston in with an appropriate tool and install the snapring.
  4.  


NOTE
Be careful not to scratch the piston cups when installing the piston assemblies.

  1. Maintain pressure on the piston an install the stopper bolt and gasket hand tight. Torque stopper bolt to 57 ft. lbs. (RWD I-Mark 14 ft. lbs.).
  2.  
  3. Install the proportioning valve, if equipped. Torque to 29 ft. lbs.
  4.  
  5. Install the grommets, fluid reservoir and attaching screw.
  6.  
  7. Install the dust seal (if equipped) with the notch at the bottom.
  8.  
  9. Press the piston all the way into the cylinder and release several times. Check for smooth piston return and brake fluid being forced from the front and rear outlets.
  10.  
  11. Fill the reservoir with fluid and bleed the master cylinder.
  12.  
  13. Torque master cylinder nuts and brake line fittings to 12 ft. lbs. After installation, bleed the brake system.
  14.  

 
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