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front disc problem

Discussion in 'Builds and Fabricators Forum' started by 66cj6tuxpark, Feb 9, 2008.

  1. Feb 9, 2008
    66cj6tuxpark

    66cj6tuxpark New Member

    Tucson, AZ
    Joined:
    May 9, 2005
    Messages:
    33
    OK, its been a while since I've worked on my cj-6, and a heck of a lot longer since I've logged on here, but I've decided that this weekend I'm going to set to it and get road worthy again. On with the problem. Some time ago I swapped disc brakes on the stock front using cj rotors and Chevy calipers. At the same time I rebuilt the stock 9 inch drums in the rear. It stops great, but as soon as I back-up, hit the brakes, and then continue forward, the pedal goes to the floor. I can pump it back up, but it has put me in some scary situations. I do have a 2lb residual valve in-line in the front with the one in the master cylinder removed. I am also using the later frame mount dual master. I don't have a proportioning valve installed. Does anyone have any ideas?
     
  2. Feb 9, 2008
    bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    K-Town Tenn.
    Joined:
    Apr 29, 2007
    Messages:
    3,294
    sounds like you have air in the lines somewhere,needs to be bled again?
    Jim S.
     
  3. Feb 9, 2008
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
    Joined:
    Sep 22, 2002
    Messages:
    5,349
    You should have 2 residual pressure valves, 1 for the disk and 1 for the drums. And yes it does sound like you have air in the lines still. Speed bleeders would help greatly in this case.
     
  4. Feb 9, 2008
    66cj6tuxpark

    66cj6tuxpark New Member

    Tucson, AZ
    Joined:
    May 9, 2005
    Messages:
    33
    I must have bled the brakes 20 times while I was fiddling with it - but I am definately going to do it again. I left the original valve in the master for the rear. Somehow, I think it is a mechanical problem - maybe I did something wrong in the rear? I just got the jeep going this morning and drove it around again, the pedal is very firm and it stops from speed (60) pretty good, but not great. I haven't gotten the brakes to go out, but I haven't tried. I think I am going now to go see when exactly it happens.
     
  5. Feb 9, 2008
    66cj6tuxpark

    66cj6tuxpark New Member

    Tucson, AZ
    Joined:
    May 9, 2005
    Messages:
    33
    OK - new symptom. After prolonged tight maneuvering or corners the brakes go out. Specifically when turning RIGHT only, after say 2 or 3 "doughnuts" at 10-15 mph. I could NOT get the brakes to go out only by going backwards and then forward or by turning only left for any period of time. It could be that previously I only noticed it after going back because I was making tighter turns at those times. I'm going out now to bleed the brakes again to see if that helps at all.

    Also - the front brakes lock up well before the rear, but if I put more pressure the rears also lock up.
     
    Last edited: Feb 9, 2008
  6. Feb 10, 2008
    runnamuck

    runnamuck look out!

    hickory, nc
    Joined:
    Nov 7, 2005
    Messages:
    223
    is the caliper contacting anything when you turn, causing the piston in the caliper to be compressed, pushing back fluid into the master cylinder? this would allow an out of spec air gap between rotor/pads that has to be refilled by pumping the brakes when steering is strait.

    make sense?
     
  7. Feb 11, 2008
    mortten

    mortten I can’t put my finger on it 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Peninsula, Ohio
    Joined:
    Apr 17, 2006
    Messages:
    1,738
    If the rears are drum then you would need the original 10 lb valve to overcome the return spring tension.
     
  8. Feb 11, 2008
    mruta

    mruta I drank with Billy!

    Downers Grove, IL
    Joined:
    Sep 22, 2002
    Messages:
    422
    What do you mean by "go out"?
     
  9. Feb 11, 2008
    n6ifp

    n6ifp Member

    San Bruno/...
    Joined:
    Sep 15, 2004
    Messages:
    206
    Is the bump stop still on the right side of the front axle. I didnt notice mine contacting the stop. The brakes would go away on right turns only. In right hand turns the right caliper hits the bup stop and compresses the caliper. The brakes would pump back up with 2 or 3 pumps. Larry
     
  10. Feb 14, 2008
    66cj6tuxpark

    66cj6tuxpark New Member

    Tucson, AZ
    Joined:
    May 9, 2005
    Messages:
    33
    When I say go out I mean that when I press on the pedal it goes to the floor and the jeep does not stop. Though, it does pump right back up.
    n6ifp- I do still have the bumpstop on the axle. I don't know if that is hitting (never looked at it), so I am going to check it out.
    I also did bleed the brakes again, and that didn't seem to help.
     
  11. Feb 15, 2008
    jzeber

    jzeber Well-Known Member 2022 Sponsor

    Morgan Hill, Ca
    Joined:
    Nov 15, 2003
    Messages:
    3,323
    When I first did my disc swap I had a similar problem. Not sure how your brake lines are set up but along the way I moved front brake line to rear brakes and rear brake line to front brakes. Corrected the problem completely. I now have full pedal and can lock front. Might be worth a try.
     
  12. Feb 16, 2008
    66cj6tuxpark

    66cj6tuxpark New Member

    Tucson, AZ
    Joined:
    May 9, 2005
    Messages:
    33
    N6ifp was right - the caliper hits the bumpstop bracket on the axle, causing the brakes to stop working. Thanks.
     
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