A power booster helps assist pushing the master cylinder piston when you apply the brakes.
A bad power booster will give a very hard pedal, it will feel like you need two feet to stop the car.
For lighter weight vehicles like street rods a 7" booster will work fine for disc/drum set ups. For a 4 wheel disc system a 7" booster will not give enough assist. An 8" dual diaphragm booster is the ticket for 4 wheel disc.
No. The booster will never cause a low or soft pedal, check for air or other hydraulic problems. A failed booster will only cause the pedal to become hard or not return.
Check the vacuum source to the booster. Not only does the booster need at least 15 in. Hg, it also needs vacuum volume. The fitting normally on the intake manifold or carburetor will get clogged with carbon build up and restrict the vacuum volume.
Replace all brake fluid. Brake fluid is hygroscopic which means it absorbs moisture. Too much water in brake fluid will cause vapor lock and apply pressure to the wheels. Also, carefully check for proper push rod adjustments and stop light/cruise control switch adjustments.
Check for a seized caliper/wheel cylinder, pinched or restricted brake line. Next check vacuum source. Check for at least 15 in Hg. Next check vacuum volume. TIP: An easy test is to park a vehicle with a good brake pedal next to your car and run the vacuum to booster in question. If pedal is OK now, vacuum source is insufficient.
This is usually a normal noise made during brake application due to atmospheric air entering the booster filter located around the push rod. Tip: Moving the silencer (foam seal) may reduce noise level.
Check for gas vapors in the booster. If the vehicle's PCV is clogged, gas vapors will enter the booster and dry up the diaphragm. Repairing PCV system and installing a charcoal vacuum filter will eliminate problem.
Replace both master cylinder and brake booster.
Typically you should expect about 1.0MPA. to the wheels for a disc brake system. A disc brake system requires this amount of pressure so be careful when using a smaller 7" booster that puts out only 0.9MPA pressure.
For a brake booster to function properly you will need at least 16" of vacuum. Anything lower will give you a hard pedal.
Sure. Just be sure to they have same brake master cylinder.