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power brakes problem

Discussion in 'Early CJ5 and CJ6 Tech' started by bkd, Mar 5, 2008.

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  1. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    so the brakes I installed on the 6 came from the donor M38A1.....discs up front/ drums in back. Power booster w/ duel master. I installed a wilwood porportioning valve for the rears, and a line lock in front.
    When I hit the brakes I blow through 60-70% of travel before the brakes engage, brakes work well enough from that point. I've bled and don't think I have air (they don't pump up any differantly) and I've got good vacuum to the booster.
    What else should I check? and how to go about it?
    Thanks all, Jim S.
     
    bkd, Mar 5, 2008
    #1
  2. kaiser_willys

    kaiser_willys Well-Known Member

    brakes adjusted properly? linkage to master cylinder adjusted properly? other than that dont know,m38a1 didnt have disk brakes, got the correct mastercylinder for disk?
     
    kaiser_willys, Mar 5, 2008
    #2
  3. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    discs up front on a Dana30....back drums have self adjusters....no real linkage to adjust from pedal arm to master, solid rod that came w/ it....booster and master came w/ the donor, is a master specific to disc?, that's why I got the P valve.......info on the setup but I'm not sure if what I have should work or needs to be modded/ changed
    Jim S.
     
    bkd, Mar 5, 2008
    #3
  4. kaiser_willys

    kaiser_willys Well-Known Member

    disc brakes have a larger piston and resivoir in the mastercylinder, shoot us some pictures of the master
     
    kaiser_willys, Mar 5, 2008
    #4
  5. kaiser_willys

    kaiser_willys Well-Known Member

    oh yes there is adjustment to the master, it is on the booster between the two:beer:
     
    kaiser_willys, Mar 5, 2008
    #5
  6. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    [​IMG][​IMG]
    heres a couple shots
     
    bkd, Mar 5, 2008
    #6
  7. kaiser_willys

    kaiser_willys Well-Known Member

    well looks like you got the correct master, may let it sit over night and try bleeding again, thats about all i got:beer:
     
    kaiser_willys, Mar 5, 2008
    #7
  8. Homebrew2

    Homebrew2 Member

    For the sake of analysis of your prob, you said the rears have self adjusters but didn't answer if the rears were 'initially' adjusted properly (unless I missed your reply) ...
     
    Homebrew2, Mar 5, 2008
    #8
  9. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    No I didn't adjust them in the rear. When I re-did my rear axle I simply reinstalled the drums and off I went. Also in searching the archives here I didn't bench bleed the master cylinder at that time either. Just seems weird to me that I can't pump them up, that's what I'd expect if there was air ANYWHERE:?
    Jim S.
     
    bkd, Mar 5, 2008
    #9
  10. Homebrew2

    Homebrew2 Member

    In leiu of anyone making a better suggestion, try adjusting the rears, with a spoon/screw driver, until you get a slight scrape of shoes against drums. You can pump the pedal within the process to make sure the shoes are centered. I believe the "self adjusters" are only responsible for taking up minor adjustments due to wear and only when the brakes are applied when driving in reverse. I hope this is of some help :beer:
     
    Homebrew2, Mar 5, 2008
    #10
  11. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    Ok I went out and adjusted the rears, they weren't scraping, but are now. I'll give a report after driving to work tomorrow....Thanks:beer:
    Jim S.
     
    bkd, Mar 6, 2008
    #11
  12. Mcruff

    Mcruff Earlycj5 Machinist

    Which one of those lines feeds the front disk brakes?
     
    Mcruff, Mar 6, 2008
    #12
  13. lynn

    lynn Time machine / Early CJ5 HR Rep Staff Member

    Air still trapped in the calipers? Bleeder needs to be at 12:00 to get all the air out... might have to dismount the caliper and rotate the bleeder to 12:00 to bleed.
     
    lynn, Mar 6, 2008
    #13
  14. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    Good eye Mike....that first pic was initial setup, had to go back and swap lines as I had the P valve in the wrong place the first time:beer:
     
    bkd, Mar 6, 2008
    #14
  15. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    My bleeders are at 12:00 all the way around
    Driving in today there was no real change in brake feel....hit the brakes, hear a squishing as it go's through 60-70% of pedal travel, then good brakes....doesn't bottom out, or pump up
    Jim S.
     
    bkd, Mar 6, 2008
    #15
  16. nickmil

    nickmil In mothballs.

    What Homebrew2 said.
    If the rear brakes aren't adjusted correctly the shoes have to travel a long way before contacting the drum. That means the wheel cylinder pistons must travel too far. This creates a larger cavity that needs more fluid, so the master cylinder piston must travel farther than it should.
    The pic shows a disc brake master cylinder, but not necessarily the correct one for the calipers you have. Without knowing what application the m/c was for and what calipers you are using it would be hard to figure if it really is the correct m/c or not. For example, 1/2 ton trucks will use one m/c with a specific bore size for the size of wheel cylinders and calipers used on that vehicle. 3/4 ton trucks of the same make will use a m/c with a larger bore size to accomodate the larger wheel cylinders and calipers used on the larger brakes.

    I'd check rear adjustment first.
    Also, do you know if the set up worked ok before?
     
    nickmil, Mar 6, 2008
    #16
  17. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    I adjusted the rears last night....didn't make a difference this morning
    No the brakes never worked correctly on the donor...same issue, I added the P valve and Mico line lock when I swapped everything over to the 6
    Jim S.
     
    bkd, Mar 6, 2008
    #17
  18. kaiser_willys

    kaiser_willys Well-Known Member

    Good point and i agree, but not necessarily true :) My 1980 Chevy was a 3/4 ton it is now a 1/2 ton. I thought the same thing:beer: went and ordered a new master cylinder for 1/2 ton, same yr. turns out part numbers were the same for both. :rofl: Go figure, should be the way you described.:beer:
     
    kaiser_willys, Mar 6, 2008
    #18
  19. bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    I appreciate the help guys......
    I bled the brakes again, still similar results. Two things I'm considering at this point...1) I may have a bad MC...2) I used 3/16" brake lines all around, I know calipers work on pressure, drums on volume....thinking I may need to install a 3lb residual valve in the line for the drums......what do you think?
    Jim S.
     
    bkd, Mar 6, 2008
    #19
  20. Homebrew2

    Homebrew2 Member

    Just one Q: do the brakes stop your sled when you need them to, or is this a "I don't like the feel of the pedal" thing?
     
    Homebrew2, Mar 6, 2008
    #20
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