Gentlemen........
I have followed the guideline (shown below) on how to test a brake booster, but have some specific questions. I've tried to insert my questions and test results in the body of the text..... I hope it comes out in readable form.
Oh......... my pro
blem is that I have to push really hard on the brake pedal. Within the last year I have replaced brake pads, rebuilt calipers, and replaced all hydraulic hoses. This problem just recently came up, and I'm wondering if my new pads are glazed or whether the booster has gone South. I am suspecting booster is bad, but would like your confirmation.
Test Procedure Previously Posted by a forum member:
Hook up the vacuum gauge. Start the engine. Note the reading. This is your "base" reading.
• I hooked up a vacuum gauge with a “T” between the brake booster and the one-way check valve, and read about 14 in Hg vacuum at idle.
Stop the engine, disconnect the booster vacuum line and cap the port on the manifold. Start the engine, look at the gauge. If this reading is substantially higher than the base, you have a leak in the system, probably in the lines leading to the booster.
• I shut the engine off and waited about 30 seconds. The vacuum gauge held at 14 in Hg. This tells me the one-way check valve is holding and the brake booster is not leaking under this test condition.
• After shutting the engine down, with my vacuum gauge still holding 14 in Hg., I pressed the brake pedal toward the floor. I heard a “hiss” from the brake booster, and the vacuum dropped to zero.
• Starting the engine will restore vacuum, but one press of the brake pedal will cause the reading to go to 0 in. Hg., and it stays there as long as the brake pedal is depressed.
Stop the engine, remove and test the one-way valve (should be able to blow into it one way but not the other). Air should only pass in the direction indicated by the arrow printed on the top of the valve (make sure to reinstall it in the correct direction).
• I removed the one-way check valve and air flows one direction only (toward intake manifold).
Reconnect the one way valve and vacuum line to the manifold and start the engine. Watch the vac gauge as a friend depresses the brake pedal. It should dip as the pedal is depressed and return to the base reading. If it drops slowly, but returns, you have a blockage/collapse in the vac line. If it falls and does not return, you have a torn diaphragm in the booster. Especially indicative of a torn diaphragm is a hissing when the pedal is depressed.
As stated above, my vacuum gauge drops to “0” when the pedal is depressed, and the vacuum will not be restored until the brake pedal is released. My questions are……
(1) Is it normal for the vacuum to drop to “0” on one push of the pedal? Or should it just “dip”?
(2) Is it normal for the vacuum to remain at “0” while the brake pedal is pushed and held toward the floor?
(3) I know I heard the “hiss” as the vacuum dropped from 14 to 0 (engine was off). As stated above, this is an indication that a booster diaphragm is torn. Do you believe I have a torn diaphragm even though I am able to hold 14 in Hg without the brake pedal being depressed?
Thanks to all for your contributions…..
