Subaru IMPREZA 2002 Service Manual page 411

BRAKE BOOSTER
BRAKE
Brake pedal
force
Fluid pressure
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 the figure. After
bleeding air from pressure gauges, proceed to
each check.
147 N 294 N
588 kPa 1,471 kPa
(1 5 kgf, 33 Ib)
(6 kcdcm', 85 psi)
(30 kgf, 66 Ib)
(15 kg/cm2, 213 psi)
(1 )- Pressure gauge
(2) Vacuum gauge
(3) Adapter hose
(4) Vacuum hose
(5) Pedal force gauge
Air tightness check
1) Start the engine and keep it running until a vac-
uum of 66.7 kPa (500 mmHg, 19.69 inHg)
=
point A
is indicated on vacuum gauge. Do not depress the
brake pedal.
(1)
Pressure gauge
(2) Vacuum gauge
2) Stop the engine and watch the gauge. If the vac-
uum drop range is less than 3.3 kPa (25 mmHg,
0.98 inHg) within 15 seconds after stopping the en-
gine, 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 the brake pedal
with pedal force of 196 N (20 kgf, 44 Ib). Keep the
engine running until a vacuum of 66.7 kPa (500
mmHg, 19.69 inHg)
=
point B is indicated on vacu-
um gauge while the pedal is still depressed.
, B
S4M0469A
I
(1) Pressure gauge
(2)
Vacuum gauge
(3) Pedal force gauge
(4) Depress
2) Stop the 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
the engine, brake booster is functioning properly.
If defective, refer to "AIR TIGHTNESS CHECK'.
<Ref. to BR-40, INSPECTION, Brake Booster.>
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.
BR-41