Power Brake Unit; Quick Inspection, On-Vehicle Power Brake Unit Function Check; Unloaded Condition - Mazda MX-5 1990 Workshop Manual

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BRAKE SYSTEM
POWER BRAKE UNIT
Quick Inspection, On-vehicle
Power brake unit function check
(Simple method)
Step 1
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1. With the engine stopped, depress the pedal a few times.
2. With the pedal depressed, start the engine.
3. If immediately after the engine starts the pedal moves down
slightly, the unit is operating.
Step 2
1. Start the engine and let it run 1 or 2 minutes.
2. Stop the engine.
3. Depress the pedal with the usual force.
4. If the first pedal stroke is long and becomes shorter with
subsequent strokes, the unit is operating.
5. If a problem is found, inspect for damage or improper con-
nection of the check valve or vacuum hose. Repair if neces-
sary, and inspect it once again.
Step 3
1. Start the engine.
2. Depress the pedal with the usual force.
3. Stop the engine with the pedal depressed.
4. Hold the pedal down for about 30 seconds.
5. If the pedal height does not change, the unit is operating.
6. If there is a problem, check for damage or improper con-
nection of the check valve or vacuum hose. Repair if neces-
sary, and check once again.
If the nature of the problem is still not clear after following the
3 steps above, follow the more detailed check described in
"Method using tester," below.
(Method using tester)
Connect a pressure gauge, vacuum gauge, and pedal depres-
sion force gauge as shown in the figure. After bleeding the
air from the pressure gauge, conduct the test as described
in the 3 steps below.
Note
• Use commercially available gauges and pedal
depression force gauge.
a) Checking for vacuum loss
Unloaded condition
1 . Start the engine.
2. Stop the engine when the vacuum gauge indicates 500
mmHg (19.7 inHg).
3. Observe the vacuum gauge for 15 seconds. If the gauge
indicates
475-500 mmHg (18.7-19.7 inHg).
the unit is
operating.
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