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Power Brake Help

Discussion in 'Jeepster Commando and Commando Tech' started by Kalva, May 17, 2021.

  1. May 17, 2021

    Kalva 1966 V6, Koening PTO Winch

    Jul 5, 2015
    I’m at a loss, 1970 Jeepster, with some brake upgrades done by PO, front disks, brake booster. Jeepster has been sitting for some years.
    I bled the brakes and when testing locked up the wheels and blew out right rear wheel cylinder.

    Now for the brake overhaul:
    Stock Master Cylinder replaced, new Wilwood proporting valve turn to full pressure for rear, all break lines and soft brake lines replaced, stock Dana 44 with 10”drums (wheel cylinders and shoes replaced)
    Front is a 1983 Dana 30 cj7 with stock disk brakes, I haven’t changed the pads as they have meat left on them.
    I’ve bled and bled and bled the brakes, and still can not lock up the brakes front or rear, closest I get is when I ran out the booster pin to master cylinder 1/4” and then I get Decent stopping still not locking up. When engine running Brake Pedal will travel 1/2way down before feeling pressure, with engine of hard firm pedal feel.
    Any help would be appreciated,

    Attached Files:

  2. May 17, 2021

    Keys5a Sponsor

    Florida Keys
    Jan 23, 2014
    Are you trying to lock up brakes on pavement, or gravel/dirt?
    I wouldn't expect a full lockup on pavement. Years back, my brother had a bullnose Jeepster that he repowered with a 454 Chevy. It stopped very well on 10" drum brakes, and could make the tires howl on hard stops on paving, but it wouldn't lock the brakes.
  3. May 17, 2021

    Kalva 1966 V6, Koening PTO Winch

    Jul 5, 2015
    Donny, yes it’s on pavement, my buddy has a bull nose and can stop very well.
  4. May 18, 2021

    dnb5853 Member 2021 Sponsor

    Grand Mesa, CO
    Aug 13, 2006
    While you might not be able to lock the brakes, you should come close to it. I can with my 1982 CJ power brake modification.
    Your initial pedal travel seems excessive. Boosters are expensive, but it sounds like you've eliminated everything else. There's usually a reasonable core exchange on boosters. That's my 2 cents.
  5. May 19, 2021

    jzeber Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Morgan Hill, Ca
    Nov 15, 2003
    Sure sounds like air in the system. Try this for bleeding the discs. Take the caliper off and place a block of wood between the pads. Lift the caliper as high as you can and bleed as you normally would. I had this same issue and it worked for me.
  6. May 22, 2021

    Lockman OK.....Now I Get It . 2022 Sponsor 2021 Sponsor 2020 Sponsor

    White City, NY 14617
    Dec 4, 2018
    Also..... Where is your vacuum line originating at ?
  7. May 24, 2021

    commanlerwrangdo Member 2021 Sponsor 2020 Sponsor

    Cleveland, Ohio
    Feb 10, 2014
    The new master is stock for the Jeepster? If so, It wont be able to feed 2 calipers correctly. Most disc/drum masters have one larger reservoir because of the amount of fluid that moves into caliper versus a wheel cylinder. If it is a disc/drum master then I have to ask if you bench bled the master before installing it.
    Lockman likes this.
  8. May 25, 2021

    jeepdaddy2000 Member

    Eagle Point oregon
    Jun 24, 2004
    A couple of things....
    Insure the rear drums are adjusted. If they are not, then you will have excessive pedal travel.
    The brake booster push rod should be just shy of the piston. If you adjusted it 1/4" with a simple MC swap, I would be looking there to start.

    An easy way to isolate brake issues is to pop a pair of vise grips on each soft line (3, one rear and one front for single MC, two front for duals). Your pedal should be brick hard. If it isn't, then you issue is between the grips and the MC.
    If the pedal is hard, then release the rear grips to one axle and see what happens. If the pedal stays hard, then put them back on and test the other axle. Once you get the soft pedal, you have found the offending axle (or caliper) and can focus your energy there.

    Side note. disc MC's don't have residual valves for the caliper end. If you are running a stock drum MC with disc's, be sure yours are removed or the discs can drag.
    Also, the large reservoir for the disc side is there because, unlike drums, the disk brake "adjustment" entails the piston continuing to move toward the disc without retracting as the pads wear. The added fluid is to compensate for this. That being said, an easy way to monitor your disc pad wear is to keep an eye on your fluid level.
    Kalva and commanlerwrangdo like this.
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