Subaru Legacy III (2000-2003 year). Manual - part 819

BR-34

BRAKE

BRAKE BOOSTER

9. Brake Booster

A: REMOVAL

CAUTION:
If external force is applied from above when 
brake booster is placed in this position, the res-
in portion as indicated by “P”, may be dam-
aged.

1) Pull up parking brake lever, and block tires.
2) Disconnect battery ground cable.
3) Remove or disconnect the following parts at en-
gine compartment.

(1) Disconnect connector for brake fluid level in-
dicator.
(2) Remove brake pipes from master cylinder.
(3) Remove master cylinder installing nuts.
(4) Disconnect vacuum hose from brake boost-
er.

4) Remove the following parts from the pedal
bracket.

(1) Snap pin and clevis pin
(2) Four brake booster installing nuts

5) Remove brake booster while shunning brake
pipes.

NOTE:
• Be careful not to drop brake booster. Brake
booster should be discarded if it has been dropped.
• Use special care when handling operating rod.
If excessive force is applied to operating rod, suffi-
cient to cause a change in the angle in excess of

±

3

°

, it may result in damage to the power piston cyl-

inder.
• Use care when placing brake booster on the
floor.
• Do not change the push rod length. If it has been
changed, reset the projected length “L” to the stan-
dard length.

Standard:

Without VDC

L = 10 mm (0.39 in)

With VDC

L = 1.8 mm (0.071 in)

B: INSTALLATION

1) Mount brake booster in position.
2) Connect operating rod to brake pedal with clevis
pin and snap pin.

(1) Force

BR-00075

( 1 )

P

(1) Nuts

(2) Clevis pin

(3) Snap pin

(4) Operating rod

BR-00074

L

BR-00073

( 1 )

( 2 )

( 3 )

( 4 )

BR-35

BRAKE

BRAKE BOOSTER

3) Connect vacuum hose to brake booster.

4) Mount master cylinder onto brake booster.
5) Connect brake pipes to master cylinder.
6) Connect electric connector for brake fluid level
indicator.
7) Adjust operating rod of brake booster.

Standard: L

LHD: 144.6 mm (5.69 in)
RHD: 173.2 mm (6.82 in)

If it is not in specified value, adjust it by adjusting
brake booster operating rod.

8) Measure the clearance between threaded end of
stop light switch and stopper.
If it is not in specified value, adjust it by adjusting
position of stop light switch.

CAUTION:
Be careful not to rotate stop light switch.

Stop light switch clearance: A

0.3 mm (0.012 in)

9) Apply grease to operating rod connecting pin to
prevent it from wearing.
10) Bleed air from brake system.

Tightening torque (Air bleeder screw):

8 N·m (0.8 kgf-m, 5.8 ft-lb)

11) Conduct road tests to ensure brakes do not
drag.

C: INSPECTION

1. OPERATION CHECK (WITHOUT GAUG-
ES)

CAUTION:
When checking operation, be sure to securely 
apply the hand brake.
• Checking without gauges

This method cannot determine the exact portion
which has failed, but it can provide a rough under-
standing of the nature of the failure if checking is
conducted in accordance with the following proce-
dures.
• Air tightness check

Start engine, and run it for 1 to 2 minutes, then turn
it off. Depress brake pedal several times applying
the same pedal force as that used in ordinary brak-
ing operations. The pedal stroke should be greatest
on the 1st depression, and it should become small-
er with each successive depression. If no change
occurs in the pedal height while in a depressed
state, brake booster is faulty.

NOTE:
• In the event of defective operation, inspect the
condition of the check valve and vacuum hose.
• Replace them if faulty and conduct the test
again.
• If no improvement is observed, check precisely
with gauges.

BR-00078

BR-00076

L

BR-00079

A

(1) OK

(2) NOT OK

(3) 1st

(4) 2nd

(5) 3rd

BR-00080

( 3 )

( 4 )

( 5 )

( 1 )

( 2 )

BR-36

BRAKE

BRAKE BOOSTER

• Operation check

1) With engine off, depress brake pedal several
times applying the same pedal force and make
sure that the pedal height does not vary with each
depression of the pedal.

2) With brake pedal depressed, start engine.
3) As engine starts, brake pedal should move
slightly toward the floor. If no change occurs in the
pedal height, brake booster is faulty.

NOTE:
If faulty, check precisely with gauges.
• Loaded air tightness check

Depress brake pedal while engine is running, and
turn off engine while the pedal is still depressed.
Keep the pedal depressed for 30 seconds; if no
change occurs in the pedal height, brake booster is
functioning normally; if the pedal height increases,
it is faulty.

NOTE:
If faulty, check precisely with gauges.

2. OPERATION CHECK (WITH GAUGES)

CAUTION:
When checking operation, be sure to securely 
apply the hand brake.
• Checking with gauges

Connect gauges as shown in Figure. After bleeding
air from pressure gauges, proceed to each check.

• Air tightness check

1) Start engine and keep it running until a vacuum
of 66.7 kPa (500 mmHg, 19.69 inHg) = point A is in-
dicated on vacuum gauge. Do not depress brake
pedal.

2) Stop 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, 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

(1) When engine is stopped

(2) When engine is started

BR-00081

( 1 )

( 2 )

(1) Pressure gauge

(2) Vacuum gauge

(3) Adapter hose

(4) Vacuum hose

(5) Pedal force gauge

(1) Pressure gauge

(2) Vacuum gauge

BR-00082

( 3 ) ( 4 )

( 5 )

( 1 )

( 2 )

BR-00083

( 1 )

( 2 )

A

BR-37

BRAKE

BRAKE BOOSTER

• 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 engine and depress brake pedal with pedal
force of 196 N (20 kgf, 44 lb). Keep 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 engine and watch vacuum gauge.
If the vacuum drop range is less than 3.3 kPa (25
mmHg, 0.98 inHg) within 15 seconds after stopping
engine, brake booster is functioning properly.
If defective, refer to “AIR TIGHTNESS CHECK”.
<Ref. to BR-35, INSPECTION, Brake Booster.>

(1) Pressure gauge

(2) Vacuum gauge

(3) Pedal force gauge

(4) Depress

BR-00084

( 3 )

( 4 )

( 1 )

( 2 )

B