To test, remove the vacuum hose from the booster and start the engine
- Fault 1...Ruptured Diaphragms in both Hydrovacs and Mastervacs.
Result...Engine will idle faster and may stop when applying the brakes.
- Fault 2...Seal failure in Hydrovacs only, causing an internal fluid leak. Result...Fluid will be sucked out of the booster and into the motor and will burn and cause eventual brake failure once the master cylinder is empty of brake fluid
- Fault 3...Reduction, or loss, of vacuum supply in both Hydrovacs and Mastervacs. Result...The reduction or loss of vacuum supply will result in a hard pedal and poor braking.
A vacuum gauge should read 20Hg on the overrun. Just putting a finger over the hose end is not conclusive. Depending on age and condition, the hose may be heat and fuel affected and could collapse when the air gets sucked out of it.
If you have any doubts, replace the vacuum hose and examine the external check valve. You should be able to suck air in through the valve, but not out. Power Brakes' facilities and collective experience are available to identify and correct all these problems.