Low Brake Pressure, 67 Chevy Impala w/power brakes
Low brake pressure – I think. Have 700 psi at the new front upgraded calibers, and 600 psi at the stock rear drum brakes. Everything I have read states a minimum requirement of 1200 to 1400 psi at the front calibers and 600 to 1000 psi at the rear drum brakes.
Quick background – everything is new except the power booster. Upgraded the front drum brakes with a Performance OnLine conversion kit, replaced all brake lines, rear wheel cylinders, and master cylinder and proportioning value (both designed for front disc and rear drum brakes). The reason I did not replace the power booster is based on the fact that it passed all checks as noted below, including tests for the power booster check valve. As an additional note, have 17.5 #s vacuum from manifold to the power booster. Hose not blocked and could find no leaks.
Booster checks performed:
1. Pump the brake pedal a few times with the engine shut off. Depress the brake pedal and hold it down. Start the engine. The brake pedal should almost immediately drop slightly, and the pedal should change from a high and hard feel to a normal feel. If it does not then this indicates a problem with the brake power booster, or possibly a low engine vacuum or plugged vacuum hose. 2. Run the engine for a few minutes. Turn the engine off and then immediately depress the brake pedal four or five times. The brake pedal should feel harder with each push, and it should come to a stop at a higher position each time. If the pedal returns to the same position each time then it indicates a problem with the brake power booster. 3. Run the engine for a few minutes. Depress brake pedal and hold it down. Turn the engine off and keep the brake pedal depressed for 30 seconds of so. The brake pedal height should not change during this time. If the pedal rises it indicates a problem with the brake power booster. As noted, all tests passed.
Any suggestions as to where I should look next or any additional tests will be appreciated. Thanks Bob