Power Brakes Failing

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  • Eugene G.
    Frequent User
    • August 1, 1982
    • 62
    #1

    Power Brakes Failing

    I have a 1970 300hp,automatic with power brakes. I took the car out ffor a morning drive. On the way home
    , everytime I stepped on the brake, the emergecy brake light would flash and the brake pedal was pretty close to the floor.
    When I got home I checked the master cylinder and both reservoirs were full.
    Is it possible my booster has a problem.
    Would appreciate any input.
    Thank you,
    Gene Gamache
    Tags: None
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    • Bill B.
      Very Frequent User
      • August 2, 2016
      • 300
      #2
      Re: Power Brakes Failing

      Gene,

      The Power Booster should not affect the BRAKE light illumination. The brake light is activated by the switch located in the brass brake "T" , located on the frame just behind the left front A-Arm. If I were to guess, it is the Master Cylinder that is the cause, with the front half and rear half creating unequal pressures when you press your pedal. Because of your reported pedal travel, I'd guestimate one of the chambers is being bypassed due to a broken O-ring internal to the Master. Because you reported both reservoirs were full, that rules out a leaking line/caliper as cause for the unequal pressure. I'd still look for a leak of brake fluid, as it does not take much fluid loss to cause the symptoms reported.
      Bill Bertelli
      Northeast and Carolinas Chapters Member
      '70 Resto Mod LT-1 w/ partial '70 ZR-1 drivetrain
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        • Eugene G.
          Frequent User
          • August 1, 1982
          • 62
          #3
          Re: Power Brakes Failing

          Bill,
          Thank you very much for your reply. The master cylinder has been on the car a long time and a rebuiid is probably long overdue.
          Thanks again.
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            • Patrick H.
              Beyond Control Poster
              • December 1, 1989
              • 11535
              #4
              Re: Power Brakes Failing

              Thankfully the rebuild kits are now once again available.
              Vice-Chairman (West), Michigan Chapter NCRS
              71 "deer modified" coupe
              72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
              2008 coupe
              Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.
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                • Eugene G.
                  Frequent User
                  • August 1, 1982
                  • 62
                  #5
                  Re: Power Brakes Failing

                  Patrick,
                  Can you tell me who supplies the rebuild kits?
                  thank you
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                    • Patrick H.
                      Beyond Control Poster
                      • December 1, 1989
                      • 11535
                      #6
                      Re: Power Brakes Failing

                      Raybestos makes them
                      MK501
                      Vice-Chairman (West), Michigan Chapter NCRS
                      71 "deer modified" coupe
                      72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                      2008 coupe
                      Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.
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                        • Eugene G.
                          Frequent User
                          • August 1, 1982
                          • 62
                          #7
                          Re: Power Brakes Failing

                          Patrick,
                          Thank you for the info.
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                            • Joe L.
                              Beyond Control Poster
                              • February 1, 1988
                              • 43129
                              #8
                              Re: Power Brakes Failing

                              Originally posted by Eugene Gamache (5884)
                              Patrick,
                              Thank you for the info.


                              Eugene------


                              However, if there is ANY corrosion or damage to the master cylinder bore, you will have to have it sleeved before installing the rebuild kit.
                              In Appreciation of John Hinckley
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                                • Patrick H.
                                  Beyond Control Poster
                                  • December 1, 1989
                                  • 11535
                                  #9
                                  Re: Power Brakes Failing

                                  I used some EvapoRust in mine to remove the rust staining (no pits) and it worked great.
                                  No leaks at this point 2 years later.
                                  Vice-Chairman (West), Michigan Chapter NCRS
                                  71 "deer modified" coupe
                                  72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
                                  2008 coupe
                                  Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.
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                                    Comment

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