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1957 rough idle when applying the brakes

Discussion in '1955 - 1966 Classic Ford Thunderbird' started by Mike Geary, May 26, 2018.

  1. Hi gang, here's another one for you, my 57 runs smoothly and idles well but when I apply the power brakes, the idle raises several hundred rpms and the engine runs a little rough. I would guess it has to do with vacuum but there doesn't appear to be any vacuum leak. Any suggestions out there? Mike
    Last edited by a moderator: May 26, 2018
  2. Dick Rupp

    Dick Rupp Active Member Lifetime Donor

    Mike, if you have power brakes check the power brake booster and hose. Listen for an air leak when you push the brake pedal
  3. Air is leaking thru the booster canister and into your intake manifold, leaning out the mixture, thus the RPM increase and rough idle. It's probably the seal that closes off the vacuum to the atmospheric side but it could also be a leak in the main diaphragm. Should be an easy fix once you find the source.
  4. I'm a little lost, are there rebuild kits for the boosters? Could you elaborate a little more on that please? Mike
  5. Yes, you can buy rebuild kits and in some cases individual parts to fix a problem. Take the booster apart and see what parts you'll need. If the main diaphragm is bad you can tell right away. If it's not then replace the seals (they'll be part of a rebuild kit) and any other parts that look tired and you should be good to go. No need to replace to whole unit unless it's worn out, or if you don't want to rebuild it yourself you can get a rebuilt unit on an exchange basis.
  6. One last question, who sells the rebuild kits? I've only had this Thunderbird for several months and it's entirely a learning experience for me. Thanks, Mike
  7. Casco or Hills Thunderbird Center have kits, parts and complete units.
  8. Okay, thank you both forgetting me going in the right direction. Mike

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