300M V6-3.5L VIN G (2000)
Vacuum Brake Booster: Testing and Inspection
BASIC TEST
1. With engine off, depress and release the brake pedal several times to purge all vacuum from the power brake booster.
2. Depress and hold the pedal with light effort (15 to 25 lbs. pressure), then start the engine.
The pedal should fall slightly, then hold. Less effort should be needed to apply the pedal at this time. If the pedal fell as indicated, perform the
VACUUM LEAK TEST listed after the BASIC TEST. If the pedal did not fall, continue on with this BASIC TEST.
3. Disconnect the vacuum hose on the side of the vacuum check valve that leads to the speed control, then connect a vacuum gauge to the open
vacuum port on the valve.
4. Start the engine.
5. When the engine is at warm operating temperature, allow it to idle and check the vacuum at the gauge.
If the vacuum supply is 12 inches Hg (40.5 kPa) or more, the power brake booster is defective and must be replaced. If the vacuum supply is
below 12 inches, continue on with this BASIC TEST.
6. Shut off the engine.
7. Connect the vacuum gauge to the vacuum reference port on the engine intake manifold.
8. Start the engine and observe the vacuum gauge.
If the vacuum is still low, check the engine tune and repair as necessary. If the vacuum is above 12 inches, the hose or check to the booster has a
restriction or leak.
Once an adequate vacuum supply is obtained, repeat the BASIC TEST.
VACUUM LEAK TEST
1. Disconnect the vacuum hose on the side of the power brake booster vacuum check valve that leads to the speed control, then connect a vacuum
gauge to the open vacuum port on the valve.
2. Remove the remaining hose on the vacuum check valve that is not the vacuum supply hose coming from the intake manifold. Cap off the open port
on the check valve.
3. Start the engine.
4. Allow the engine to warm up to normal operating temperature and engine idle.
5. Using vacuum line pliers, close off the vacuum supply hose near the booster and observe the vacuum gauge.
If the vacuum drop exceeds 1.0 inch Hg (3.3 kPa) in one minute, repeat the above steps to confirm the reading. The vacuum loss should be less
than 1.0 inch Hg in one minute time span. If the loss is more than 1.0 inch Hg, replace the power brake booster. If it is not, continue on with this
test.
6. Remove the pliers from the hose temporarily.
7. Apply light effort (approximately 15 lbs. of force) to the brake pedal and hold the pedal steady. Do not move the pedal once the pressure is applied
or the test results may vary.
8. Have an assistant reattach the pliers to the vacuum supply hose.
9. Allow 5 seconds for stabilization, then observe the vacuum gauge.
If the vacuum drop exceeds 3.0 inches Hg (10 kPa) in 15 seconds, repeat the above steps to confirm the reading. The vacuum loss should be less
than 3.0 inches Hg in 15 seconds time span. If the loss is more than 3.0 inches Hg, replace the power brake booster. If it is not, the booster is not
defective.
