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‘72 Brake Bleed Help

Discussion in 'Intermediate CJ-5/6/7/8' started by rusty72cj5, Sep 25, 2021.

  1. Sep 25, 2021
    rusty72cj5

    rusty72cj5 Member

    Florida
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    I’ve bench bled the replacement MC until there were no more bubbles. I’ve replaced all the shoes, springs, and adjusted them to decent resistance when I try to spin the wheels. I’ve bled all 4 WC’s in the proper order getting fluid at all 4 without bubbles. I can’t get any pedal whatsoever. I know from the TSM that I’ll have to drive back and forth a few times for everything to adjust before a road test, but shouldn’t I get something on the pedal before that point? Is there something I’m forgetting? Should I continue to force more fluid out at the WC’s? This is a ‘72 so I don’t have a proportioning valve. New to setting this all up from scratch.
     
  2. Sep 25, 2021
    Lockman

    Lockman OK.....Now I Get It . 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Did you have a helper pump & hold the pedal while you bled the wheel cylinders ? If you did that, I'm guessing it's in your master cylinder ? Once all the air is out, you should have pedal ?
     
  3. Sep 25, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    I'm thinking that at least one shoe is not adjusted well. Maybe one of a pair that is not centered?

    Have you re-checked the adjustments after pumping hard?
     
    SoFla8300 likes this.
  4. Sep 25, 2021
    melvinm

    melvinm Member

    Arvada Co. 80003
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    Do You have residual valves in Your Master cylinder or in the brake lines.
    Drum brake require 10 psi residual valves .
     
  5. Sep 25, 2021
    Iandavidh

    Iandavidh Member

    California
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    Make sure all of your rubber lines are in good shape they could be clogging things up
     
  6. Sep 25, 2021
    rusty72cj5

    rusty72cj5 Member

    Florida
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    Regarding the residual check valves, I would assume they are present in the MC behind the tube seats as the diagram in my TSM shows since what I ordered was listed as a direct replacement. Never considered they might not be. I didn’t see any additional valves in the lines when I re-did everything copying what was originally there. I guess I could add some but I don’t have experience with that as far as where to put them. I’ll have to get her up on jack stands and look everything over again as far as the shoes and a possible misalignment. I thought everything was back in place correctly though and things seemed to tighten up against the drums correctly via the adjusting screws. Doesn’t seem to do anything when Pump fast or hard. Just nothing there at all but I do get fluid coming out at all the WCs. I’m so close to the end of this 5 year project. Thanks for all the help guys. Couldn’t have rebuilt this thing from the ground up without all the tips.
     
  7. Sep 26, 2021
    rusty72cj5

    rusty72cj5 Member

    Florida
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    This is the procedure from the TSM that I used to bench bleed the MC. Fashioned the curved rerun tubes as described. The bubbles eventually stopped but the push rod never got really super difficult to push in, just some increased resistance. Should it have gotten really difficult to push in at some point causing me to have to get on it really hard as it competed it’s bleeding? If so, I either didn’t bleed it long enough or I have a bad MC I possibly.
     

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  8. Sep 26, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Re Pete's comment that it may not be adjusted as well as you think, one loose pair of shoes could suck up a lot of master cylinder volume.

    I use the drum brake calipers to set up the shoe clearance. However, if you adjust with a spoon through the slot in the backing plate, you should tighten the shoes as much as possible, then back them off until you can turn the drum/wheel. It helps to use a screwdriver along with the spoon to lift the self adjuster pawl off of the toothed wheel.

    If you have the original brakes with no additions, you should be able to follow the bleeding instructions in the TSM. These books are meant for the line mechanics (called technicians today) and will not educate you on basic processes like brake bleeding. Also, a dealership would not mess around with pumping the brakes and instead use a power bleeder. I have one, and it's the best way to do this. That along with the drum brake caliper, and you'll be servicing drum brakes like the pros would (in the day).

    https://www.amazon.com/GearWrench-3377-Brake-Resetting-Gauge/dp/B0002SQUJ0/ref=sr_1_4
    https://www.amazon.com/dp/B0002KM5L0/?tag=bnr2-20
    https://www.amazon.com/Motive-Products-1105-Cylinder-Adapter/dp/B000TYHZM8?ref_=ast_sto_dp
     
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  9. Sep 26, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    x2
     
  10. Sep 26, 2021
    sterlclan

    sterlclan Member 2022 Sponsor

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    I dont pump the pedal before opening the bleeder. two people, one to push the pedal down,then the other opens the bleeder, and before the first lets up close the bleeder. pumping can make a large bubble into a ton o small ones.
     
  11. Sep 26, 2021
    Lockman

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    If you have done all this , above, then the problem is in your MC. You can rebleed it on the Jeep, & I suggest that is what you do. I had to do mine that way ; chasing a similar problem. I'm sorry ........New systems can be a Pita :censored::confused::rolleyes:
     
  12. Sep 30, 2021
    rusty72cj5

    rusty72cj5 Member

    Florida
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    Well, back for Paul Harvey’s rest of the story. I adjusted all the wheels to full stop again, then backed them off following TSM instructions. Then I bled every wheel again using the cheap hose and bottle method. Went through a lot of fluid, but….Houston, we now have a brake pedal! I think it was probably some misaligned shoes as well as me not bleeding it enough in the beginning. Front seem to be stronger than the back. But wanted to thank everyone.
     
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  13. Sep 30, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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  14. Oct 1, 2021
    Lockman

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    :beer:.....X2
     
  15. Oct 10, 2021
    jeepdaddy2000

    jeepdaddy2000 Active Member

    Eagle Point oregon
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    This is correct. 70% of braking is done by the front axle.
    Barring an obvious mis-balance, the fronts should always lock up before the rears.
     
  16. Oct 10, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    If I had a '72 or '73, I'd consider upgrading to add a proportioning valve. It's actually called a combination valve by Jeep, since it performs more functions than just proportioning.

    CJComboValve (458 x 634).jpg

    CJComboValve2 (472 x 248).jpg

    This is from the '75 TSM, but the '74 TSM is the same and available at the Tom Collins site.

    If the front wheels lock before the rears, in a curve you lose steering control and plow in whatever direction you are going. If you lock the rears, in a curve you can go into a spin. Ideal is to come just to the brink of locking up, since that gives you maximum braking speed while retaining steering control.

    You can buy a proportioning valve like Jeep used from Inline Tube, and other places. The only thing that might be different is the wheel cylinder sizes - I think they are all the same '72-75, but I have not checked.
     
    Last edited: Oct 10, 2021
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  17. Oct 10, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Jeep calls the residual valves "check valves" and they are clearly shown in the master cylinder picture in the TSM. If you pick the MC for the proper application, the new replacement MC comes with these already installed.
     
  18. Oct 10, 2021
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    x2. Understeer versus Oversteer.

    But IRL I'd much rather have the rears lock first, because then even the skid is potentially controllable. Experience on motorcycles will prove the sense of that preference.
     
    Lockman likes this.
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