Vacuum Brake Booster: Service and Repair
Brake BoosterREMOVAL
1) Remove or disconnect the following parts at engine compartment.
(1) Disconnect the connector for brake fluid level indicator.
(2) Remove the brake pipes from master cylinder.
(3) Remove the master cylinder installing nuts.
(4) Disconnect the vacuum hose from brake booster.
2) Remove the following parts from pedal bracket.
(1) Snap pin and clevis pin
(2) Four brake booster installing nuts
3) Remove the brake booster while shunning brake pipes.
NOTE:
^ Be careful not to drop the brake booster. The brake booster should be discarded if it has been dropped.
^ Use special care when handling the operating rod. If excessive force is applied to the operating rod, sufficient to cause a change in the angle in excess of +3°, it may result in damage to the power piston cylinder.
^ Use care when placing the brake booster on floor.
^ Do not change the push rod length. If it has been changed, reset the projected length "L" to standard length.
Standard L: 10.05 mm (0.40 inch)
CAUTION: If external force is applied from above when the brake booster is placed in this position, the resin portion as indicated by "P", may be damaged.
INSTALLATION
1) Adjust the operating rod of brake booster.
Standard L: 144.6 mm (5.69 inch)
If it is not within specified value, adjust it by adjusting the brake booster operating rod.
2) Mount the brake booster in position.
3) Connect the operating rod to brake pedal with clevis pin and snap pin.
4) Connect the vacuum hose to brake booster.
5) Mount the master cylinder onto brake booster.
6) Connect the brake pipes to master cylinder.
7) Connect the electric connector for brake fluid level indicator.
8) Measure the clearance between threaded end of stop light switch and stopper. If it is not within specified value, adjust it by adjusting the position of stoplight switch.
If it is not within specified value, adjust it by adjusting the position of stop light switch.
CAUTION: Be careful not to rotate the stop light switch.
Stop light switch clearance A: 0.3 mm (0.012 inch)
9) Apply grease to operating rod connecting pin to prevent it from wearing.
10) Bleed air from the brake system.
Tightening torque (Air bleeder screw):
Except 17 inch type: 8 Nm (0.8 kgf-m, 5.8 ft. lbs.)
17 inch type: 20 Nm (2.0 kgf-m, 14.5 ft. lbs.)
11) Conduct road tests to ensure brakes do not drag.
INSPECTION
OPERATION CHECK (WITHOUT GAUGES)
CAUTION: When checking operation, be sure to securely apply the parking brake.
^ Checking without gauges
This method cannot determine the exact portion which has failed, but it can provide a rough understanding of the nature of failure if checking is conducted in accordance with the following procedures.
^ Air tightness check
Start the engine, and run it for 1 to 2 minutes, then turn it off. Depress the brake pedal several times applying same pedal force as that used in ordinary braking operations. The pedal stroke should be greatest on 1st depression, and it should become smaller with each successive depression. If no change occurs in the pedal height while in a depressed state, the brake booster is faulty.
NOTE:
^ In the event of defective operation, inspect the condition of check valve and vacuum hose.
^ Replace them if faulty and conduct the test again.
^ If no improvement is observed, check precisely with gauges.
^ Operation check
1) With the engine off, depress the brake pedal several times applying same pedal force and make sure that pedal height does not vary with each depression of pedal.
2) With the brake pedal depressed, start the engine.
3) As the engine starts, the brake pedal should move slightly toward the floor. If no change occurs in the pedal height, the brake booster is faulty.
NOTE: If faulty, check precisely with gauges.
^ Loaded air tightness check
Depress the brake pedal while engine is running, and turn off the engine while pedal is still depressed. Keep the pedal depressed for 30 seconds; if no change occurs in the pedal height, the brake booster is functioning normally; if the pedal height increases, it is faulty.
NOTE: If faulty, check precisely with gauges.
OPERATION CHECK (WITH GAUGES)
CAUTION: When checking operation, be sure to securely apply the parking brake.
^ Checking with gauges
Connect gauges as shown in the figure. After bleeding air from pressure gauges, proceed to each check.
^ Air tightness check
1) Start the engine and keep it running until a vacuum of 66.7 kPa (500 mmHg, 19.69 in-Hg) = point A is indicated on vacuum gauge. Do not depress the brake pedal.
2) Stop the engine and watch the gauge. If the vacuum drop range is less than 3.3 kPa (25 mmHg, 0.98 in-Hg) within 15 seconds after stopping engine, the brake booster is functioning properly.
If defective, the cause may be one of those listed below.
^ Check valve malfunction
^ Leak from vacuum hose
^Leak from the shell jointed portion or stud bolt welded portion
^ Damaged diaphragm
^ Leak from valve body seal and bearing portion
^ Leak from plate and seal assembly portion
^ Leak from poppet valve assembly portion
^ Loaded air tightness check
1) Start the engine and depress brake pedal with pedal force of 196 N (20 kgf, 44 lbs.). Keep the engine running until a vacuum of 66.7 kPa (500 mmHg, 19.69 in-Hg) = point B is indicated on vacuum gauge while the pedal is still depressed.
2) Stop the engine and watch vacuum gauge.
If the vacuum drop range is less than 3.3 kPa (25 mmHg, 0.98 in-Hg) within 15 seconds after stopping engine, the brake booster is functioning properly.
If defective, refer to "AIR TIGHTNESS CHECK".
3) If any fault is found on brake booster, replace the brake booster with a new one.
^ Lack of boosting action check
Turn off the engine, and set the vacuum gauge reading at "0". Then, check the fluid pressure when brake pedal is depressed. The pressure must be greater than the standard value listed.
^ Boosting action check
Set the vacuum gauge reading at 66.7 kPa (500 mmHg, 19.69 in-Hg) by running engine. Then, check the fluid pressure when brake pedal is depressed. The pressure must be greater than the standard value listed.