Mazda MX-3 silhouetteMX-3

Power Brake Unit - Quick inspection (on-vehicle)

P-26prose procedure

Quick inspection (on-vehicle)

Power brake unit function Check (Simple method)

Step 1

  1. 1
    With the engine stopped, depress the pedal a few times.
    Step 1 illustration showing two vacuum gauges (1 and 2) above a brake pedal being depressed by a foot, with an arrow indicating the pedal moving down slightly after the engine starts.
  2. 2
    With the pedal depressed, start the engine.
  3. 3
    If immediately after the engine starts the pedal moves down slightly, the unit is operating.

Step 2

  1. 1
    Start the engine.
    Step 2 illustration showing gauges 1, 2, 3 and a foot depressing the brake pedal in successive strokes labeled FIRST, SECOND, THIRD with downward arrows indicating decreasing stroke length.
  2. 2
    Stop the engine after it has run for 1 or 2 minutes.
  3. 3
    Depress the pedal with the usual force.
  4. 4
    If the first pedal stroke is long and becomes shorter with subsequent strokes, the unit is operating.
  5. 5
    If a problem is found, inspect for damage of the check valve or vacuum hose and examine the installation. Repair if necessary, and inspect it once again.

Step 3

  1. 1
    Start the engine.
    Step 3 illustration showing gauges 1, 3 and 2, 4, with a foot holding the brake pedal down labeled FOR 30 SECONDS.
  2. 2
    Depress the pedal with the usual force.
  3. 3
    Stop the engine with the pedal held depressed.
  4. 4
    Hold the pedal down for about 30 seconds.
  5. 5
    If the pedal height does not change, the unit is operating.
  6. 6
    If there is a problem, check for damage to the check valve or vacuum hose, and check the connection. Repair if necessary and check once again.
If the nature of the problem is still not clear after the 3 steps above, follow the more detailed check described in "Method-using tester," below.

(Inspection using gauges)

Connect the SST gauges, vacuum gauge A, and pedal depression force gauge B as shown. Bleed the air from the SST gauges before performing the following tests.

a) Checking for vacuum loss - Unloaded condition

Checking for vacuum loss (unloaded condition)

  1. 1
    Start the engine.
    Checking for vacuum loss (unloaded condition) illustration showing vacuum gauges 1, 2 and a force gauge 3.
  2. 2
    Stop the engine when the vacuum gauge reading reaches 66.7 kPa {500 mmHg, 19.7 inHg}.
  3. 3
    Observe the vacuum gauge for 15 seconds. If the gauge shows 63.3—66.7 kPa {475—500 mmHg, 18.7—19.7 inHg}, the unit is operating.
Vacuum gauge reading (stop engine)unloaded
66.7kPa {500 mmHg, 19.7 inHg}
Vacuum gauge after 15 secondsunit operating
63.3—66.7kPa {475—500 mmHg, 18.7—19.7 inHg}
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