Toyota Celica/Supra 1971-1985 Repair Guide

Power Brake Booster

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Vacuum boosters can be found only on models equipped with power brakes.

Virtually all modern vehicles use a vacuum assisted power brake system to multiply the braking force and reduce pedal effort. Since vacuum is always available when the engine is operating, the system is simple and efficient. A vacuum diaphragm is located on the front of the master cylinder and assists the driver in applying the brakes, reducing both the effort and travel he must put into moving the brake pedal.

The vacuum diaphragm housing is normally connected to the intake manifold by a vacuum hose. A check valve is placed at the point where the hose enters the diaphragm housing, so that during periods of low manifold vacuum brakes assist will not be lost.

Depressing the brake pedal closes off the vacuum source and allows atmospheric pressure to enter on one side of the diaphragm. This causes the master cylinder pistons to move and apply the brakes. When the brake pedal is released, vacuum is applied to both sides of the diaphragm and springs return the diaphragm and master cylinder pistons to the released position.

If the vacuum supply fails, the brake pedal rod will contact the end of the master cylinder actuator rod and the system will apply the brakes without any power assistance. The driver will notice that much higher pedal effort is needed to stop the car and that the pedal feels harder than usual.

TESTING



Vacuum Leak
  1. Operate the engine at idle without touching the brake pedal for at least one minute.
  2.  
  3. Turn off the engine and wait one minute.
  4.  
  5. Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system.
  6.  

System Operation
  1. With the engine OFF , pump the brake pedal until the supply vacuum is entirely gone.
  2.  
  3. Put light, steady pressure on the brake pedal.
  4.  
  5. Start the engine and let it idle. If the system is operating correctly, the brake pedal should fall toward the floor if the constant pressure is maintained.
  6.  

Power brake systems may be tested for hydraulic leaks just as ordinary systems are tested.

REMOVAL & INSTALLATION



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the brake booster and master cylinder

  1. Remove the master cylinder as previously detailed.
  2.  
  3. Locate the clevis rod where it attaches to the brake pedal. Pull out the clip and then remove the clevis pin.
  4.  
  5. Disconnect the vacuum hose from the booster.
  6.  
  7. Loosen the four nuts and then pull out the vacuum booster, the bracket and the gasket.
  8.  
  9. Installation is in the reverse order of removal.
  10.  

OVERHAUL



Aisin Type

See Figures 2 and 3



Click image to see an enlarged view

Fig. Fig. 2: Exploded view of Aisin type vacuum booster components



Click image to see an enlarged view

Fig. Fig. 3: Apply silicone grease to the identified parts when assembling the Aisin vacuum booster

  1. Unscrew the nut at the front of the booster and remove the pushrod.
  2.  
  3. Loosen the retaining nut and then unscrew the clevis.
  4.  
  5. Pull off the rubber boot.
  6.  
  7. Use a screwdriver to pry out the air filter retainer from around the back of the booster and then remove the three filter elements.
  8.  
  9. Put an alignment mark across the front body, the band and the rear body.
  10.  
  11. Using Special Tool 09738-00010 or a few pieces of wood and some C-clamps, compress the rear body into the front body and remove the booster band. Separate the front and rear bodies from each other.
  12.  
  13. Carefully remove the spring retainers, the reaction plate, the reaction levers and the rubber ring.
  14.  
  15. Use snapring pliers to remove the snapring in the diaphragm plate and then pull out the operating rod toward the rear.
  16.  
  17. Using a special retainer wrench, remove the retainer and then separate the diaphragm and the plate.
  18.  
  19. Assembly is in the reverse order of disassembly.
  20.  

JKK Type

See Figures 4 and 5



Click image to see an enlarged view

Fig. Fig. 4: Exploded view of the JKK type vacuum booster components



Click image to see an enlarged view

Fig. Fig. 5: Apply silicone grease to the identified parts when assembling the JKK vacuum booster

  1. Loosen the retaining nut and unscrew the clevis. Remove the rubber boot.
  2.  
  3. Use a screwdriver to remove the air filter retainer and then pull out the two filter elements.
  4.  
  5. Put an alignment mark on the front and rear shells.
  6.  
  7. Use the Special Tool 09738-00010 or a few pieces of wood and some C-clamps to compress the rear shell into the front shell.
  8.  

If the Special Tool is used, tighten its bolts to 35-52 ft. lbs. (47-70 Nm).

  1. Turn the front shell clockwise to separate the two shells and then remove the pushrod and the spring.
  2.  
  3. Remove the diaphragm from the diaphragm plate.
  4.  
  5. Push the valve operating rod in and remove the stopper key.
  6.  
  7. Pull out the valve operating rod.
  8.  
  9. Assembly is in the reverse order of disassembly.
  10.  

 
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