Subaru 2004 LEGACY, Service Manual

Page: 493 / 609

BR-34
BRAKE
Brake Booster
• AIR TIGHTNESS CHECK
Start the engine, and idle it for 1 to 2 minutes, then
turn it OFF. Depress the brake pedal several times
applying the same pedal force as that used in ordi-
nary braking operations. The pedal stroke should
be greatest on the 1st depression, and it should be-
come smaller with each successive depression. If
no change occurs in the pedal height while in a de-
pressed state, the brake booster is faulty.
NOTE:
• In the event of defective operation, also 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.
• OPERATION CHECK
1) With the engine OFF, depress the 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 the brake pedal depressed, start the en-
gine.
3) As engine starts, the brake pedal should move
slowly 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 the pedal is still de-
pressed. Keep the pedal depressed for 30 sec-
onds; 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.
2. 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.
(1) Normal Operation
(2) Not OK
(3) 1st
(4) 2nd
(5) 3rd
(1) When engine is stopped
(2) When engine is started
(1)
(3)
(4)
(5)
(2)
BR-00080
(1) (2)
BR-00081
(1) Pressure gauge
(2) Vacuum gauge
(3) Adapter hose
(4) Vacuum hose
(5) Pedal force gauge
(1) (2)
(3) (4) (5)
BR-00082