Top Power Brake Booster Questions

  • The brake pedal is low and spongy. I guess I need to replace the booster, right?

    No. The booster will never cause a low or soft brake pedal, check for air or other hydraulic problems. A defective booster will only cause the pedal to become hard or not return.
  • After a couple of brake applications, the pedal starts to get hard. How do I fix this?

    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.
  • I replaced the booster and now the brakes are locked up and won't release. What should I do?

    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.
  • The original problem was a hard brake pedal. I replaced the booster and I still have the same thing. What do I do now?

    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.
  • I installed a new booster. Why am I hearing an air noise under the dash?

    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.
  • I replaced 3 boosters in less than 1 year. What can be causing the problem?

    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.
  • I took off my old booster and there was brake fluid between the master cylinder and booster. Which one do I replace?

    Replace both master cylinder and brake booster.
  • How do I find the correct booster for my car?

    Check the push rod stamp I.D. code and cross in the CARDONE Catalog.
  • The catalog asks if its a dual or single diaphragm booster. How can I tell?

    Most single diaphragm boosters are 10" in diameter and 4-1/2" thick. Most dual diaphragms are 9" in diameter and 6" thick.

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