Replaced front calipers rotors and pads. Still need to do rears... wile im driving car i hear a constant hissing. When i break it goes away. Let go of breaks and hissing again. Do i need a new booster?
Power brake booster test:
1.) Check engine vacuum you should have 14"-18" of vacuum at 625-750 RPM, 18"-21" vacuum at 1000 RPM.
2.) Vacuum checks good, start car and run engine up to 1000 RPM for 30 seconds.
3.) Cut off the engine and then press the brake pedal 3 times. It should get harder to press and travel less each time you press it. If it doesn't, then the brake booster is suspect.
One thing to keep in mind...the above may not address a failing booster. Mine is hissing at idle and get worse when I push on the brakes. I've done everything I can think of but I'm at my wits end so I'm just replacing my booster this coming week.