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help, brakes lock up

Discussion in 'The Hokey Ass Message Board' started by chubbie, May 31, 2012.

  1. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member

    wife wants to drive her '67 cutlass convertable (only 3 years OT?) when you step on the brakes you have nothing....nothing..BANG they lock up!!!

    I've replaced the power brake booster, 2 master cylinders, wheel cyl. and I'm thinking I replaced the hoses. most of this about 1,000 miles ago. its all drum/drum the way the general made it. no there isn't air in the lines

    question, does the brass brake line porportioning valve thing under the master ever go bad? its the only thing i havn't changed other than the lines
     
  2. rampant150
    Joined: Dec 30, 2010
    Posts: 31

    rampant150
    Member

    Does it lock up all four wheels or just one or two?
     
  3. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member

    fronts lock up
     
  4. mike hohnstein
    Joined: Dec 4, 2011
    Posts: 262

    mike hohnstein
    BANNED
    from wisconsin

    shoe's installed correctly, shorter one's in front? Lines well flushed, no pieces floating? Lock up you speak of usually comes from greasy or wet brake frictions, that doesn't seem to be the problem, but.....doubt the proportioning valve is causing the problem as far as I know it's a orifice device, no moving parts.
     

  5. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,650

    V8 Bob
    ALLIANCE MEMBER


    There's no proportioning valve in that brass thing, only a pressure differential switch and/or frt./rear distribution block. And yes, they can go bad. Sounds like you may have front brakes only. If you are sure the wheel/master cylinders and hoses are OK, I would bypass/plumb around the combo valve to eliminate that possibility. Does the brake light come on in the dash?
     
  6. 56premiere
    Joined: Mar 8, 2011
    Posts: 1,445

    56premiere
    Member
    from oregon

    well i had a simialer thing,also ot,this truck only stopped on the front,not much fun on ice.checked shoes,caliprs.back shoes were still the original ones,factory paint on all the parts.the truck was 10 years old and had never touched the shoes.i took out the valve and it was full of machining residue.put a new one on perfect brakes again.
     
  7. tommy
    Joined: Mar 3, 2001
    Posts: 14,758

    tommy
    Member Emeritus

    I added a used factory booster for my 66 SS396 build. I had the same problem. It would scare the shit out of me. I eventually ordered a high dollar rebuilt booster. When I got the rebuilt booster the only thing different that I could see was that the used booster did not have a push rod on the piston. I put the new one on and the problem went a way. I had no idea what it was supposed to look like so I just bolted the faulty booster on. I had good brakes.actually too good brakes. The problem was solved with the new rebuilt booster. I guess what I'm trying to get at is that it is possible to have a faulty booster cause the problem that you describe.
     
  8. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member


    it did the "dive" before the new booster too
     
  9. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member

    Yes i think its possible that the fronts get most of the preasure. I think the lite came on when the MC was bad.. I have a 50,000 mile parts car, it drove good before i parted it out. I should try to change out the distribution block,would make sense that its plugged and i get the big surprise when use the brakes!
     
  10. I don't even know where you can buy a new brake distribution block. You may be able to clean it, no moving parts inside it. Did you change your rear flex line? That would account for the fronts working like they are.

    Bob
     
  11. Dapostman
    Joined: Apr 24, 2011
    Posts: 294

    Dapostman
    Member

    How are the backing plates? If the wear surfaces are badly worn they can cause the shoes to hang up.
     
    Elcohaulic likes this.
  12. stainlesssteelrat
    Joined: Nov 23, 2010
    Posts: 583

    stainlesssteelrat
    Member
    from ms

    who need brakes? cut the lines.
     
  13. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member

     
  14. wizzard23
    Joined: Dec 12, 2009
    Posts: 733

    wizzard23
    Member

    Having the same problem on our drum/drum 50 Chevy with the dreaded Nova clip. Subscribed, and thank you.
     
  15. Make sure the shoes are in correctly.short shoes on the front side of each brake assy.wheel cylinder bleed screws at the top.
     
  16. Is it super sensitive? If the new booster has a short rod and the master has a deep hole like most drum drum masters had then, that combo is wrong. What happens is boosters rod can't monitor the force put to the master. It makes for a real eye opener :eek:. Don't ask me how I know ;).
     
  17. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member

    super sensitive! so you are saying this the way GM built these cars? and most cars from the '60s had the big surprise? or have i missmatched the booster/MC
     
  18. Boryca
    Joined: Jul 18, 2011
    Posts: 664

    Boryca
    ALLIANCE MEMBER
    from Detroit

  19. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,650

    V8 Bob
    ALLIANCE MEMBER


    The two-way combo valve does have a moving part, the differential pressure shuttle switch, that can leak internally and allow the primary and secondary master cylinder outputs to blend into one another. It's rare, but does happen. :)
     
  20. sic-nic
    Joined: Sep 27, 2009
    Posts: 212

    sic-nic
    Member

    my car did that until i rotated the bleeder to the top of the hub and bled the brakes again.it was full of air.
     
  21. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member

    I'm getting some good info about this, and if i don't get another chance to say...;) THANK-YOU
     
  22. You may have missmatched parts now, after installing new parts. I F'd up once and put the wrong booster on a set up much like yours. That F'n thing would send you thru the windshield. All I'm saying is, pull the master from the booster and see if the rod from the booster fits the master correctly.
     
  23. Ya learn something new every day... I'm more familiar with the older ones that were a glorified tee fitting.

    Bob
     
  24. I'm having a problem like yours, but maybe a little different. I have a '35 plymouth with 4 wheel disc. I have the m/c, booster under the floor. It has the combo valve (that's what I was told it was), the brass block, under the master. When I drive it for 30 mins. the front brakes lock up, I think from the exhaust heat. I am going to try and eliminate the brass block and see what happens with just a proportioning valve.
     
  25. FlynBrian
    Joined: Oct 5, 2007
    Posts: 759

    FlynBrian
    Member

    I've had the front rubber brake hoses go bad from being old and you couldn't tell from just looking at them by yourself. Had to get someone to push on the brakes while I visually checked the rubber hoses with pressure on them, they had deteriorated from the inside out and you could see the rubber brake hose swell up. Same symptom your having, push the brake, no brakes, then all of a sudden the fronts would lock up once the rubber hose quit swelling and the brake pressure equalized. Worth a look.
     
  26. chubbie
    Joined: Jan 14, 2009
    Posts: 2,300

    chubbie
    Member




    we have a pair of winners! 396 and Brian!!!! IT WAS THE HOSES!!!!! i changed out all 3 so i don't know witch one, but it drives great..to bad summer is over
     
  27. wizzard23
    Joined: Dec 12, 2009
    Posts: 733

    wizzard23
    Member

    Bringing this old thread up again, and yes I been on here before. Still having problems on this 50 Chevy with the front brakes wanting to do too much. If you go easy on the pedal you can pretty much get by, but there's a point where front will lock up. The car has a 72 Nova front clip with 4 wheel drum power brakes. All components were new around 30K ago except the distribution block under the master and the block pictured on the frame. I don't know what this block is for, but it was on the donor car so I installed it during the build. I thought some pictures might help, so here they are. I am using DOT5 brake fluid, but have used it in other projects with no problems. Does the plumbing off of the master look correct? Any thoughts might be a help. Thanks.
     

    Attached Files:

  28. Sheep Dip
    Joined: Dec 29, 2010
    Posts: 1,572

    Sheep Dip
    Member
    from Central Ca

    I'll second this.....my buddy's OT 69 Camaro did the same thing in the rear brakes, we changed the flex hose that drops to the rear differential out bled it and problem gone.
     
  29. What's the pedal ratio ?
     
  30. wizzard23
    Joined: Dec 12, 2009
    Posts: 733

    wizzard23
    Member

    I've wonderd if pedal ratio could be the problem, but if I remember right it's out of the Nova. Should be ok, right?
     

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