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Brake help....WTF is the issue here?

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  • Brake help....WTF is the issue here?

    Dudes (and dudettes), after a couple YEARS of wrangling paperwork on my wrecker, it is finally "legit" and able to be cruised. I am going through the truck now to get it all squared away but have hit a roadblock on the brakes. Mainly in the fact that the truck currently has none and I cannot figure it for the life of me.

    The brakes kind of degenerated over time where they went from OK to a little squishy to needing to pump the pedal to build some pressure and now to having zero pedal despite the fact that there is fluid in the lines and the master is full. I replaced the master cylinder last year while screwing around with it as I had discovered that the old one was filling the brake booster with fluid. I figured that the seals were junk and that would be that. New master is on and still no pedal. I can bleed the suckers until the cows some home and get nowhere. It is not leaking fluid onto the ground, etc.

    I always thought that the sign of a bad booster was a hard pedal, but maybe I am wrong. Any ideas are appreciated for sure!

    BTW, this truck has a very "normal" braking system with a single pot master, typical diaphragm booster, and wheel cylinders at the corners.

    Obviously something was gradually going away (when I had to start pumping the brakes a while back) and I should have fixed it then, but the hassle of trying to get the paperwork square pretty much took the fun out of cruising it.

    Whaddya think?
    That which you manifest is before you.

  • #2
    Expanding rubber lines. Change them all out.

    And are you getting good fluid movement/volume when bleeding them?
    Last edited by TheSilverBuick; June 16, 2014, 02:38 PM.
    Escaped on a technicality.

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    • #3
      First thing that comes to mind is poopy brake hoses &/or weepy wheel cylinders...

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      • #4
        leaky wheel cylinders is good, they need constant self prime the other direction. A proper leak is undetectable, or quick puff of smoke. That design was last seen in a mini version... 1980s ricers rear brakes (true story).

        every action has a reaction, maybe you got all four stuck, and its bleeding back into itself at the master, or one set feeding over to the other, self cancel.

        I remember a 50s a tow truck when I was a kid..and the brakes did this. try lid off and gently applying, see if it pressures back up through.
        It is about all I can think of and seeing this in real world.
        (that 50s tow truck BTW was the first I ever drove around a parking lot) had two shifters.
        Last edited by Barry Donovan; June 16, 2014, 02:45 PM.
        Previously boxer3main
        the death rate and fairy tales cannot kill the nature left behind.

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        • #5
          this thing?

          My fabulous web page

          "If it don't go, chrome it!" --Stroker McGurk

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          • #6
            simply because it's a new master cylinder doesn't mean it works - don't ask me how I know this
            Doing it all wrong since 1966

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            • #7
              Does it have a prop valve? If so, it could be stuck one way and need to be recentered. I ran into that with my truck. Drove me crazy until I got it recentered. Now they work awesome.
              Life is short. Be a do'er and not a shoulda done'er.
              1969 Galaxie 500 https://bangshift.com/forum/forum/ba...ild-it-s-alive
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              1973 F-250 BBF Turbo Truck http://www.bangshift.com/forum/forum...uck-conversion
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              • #8
                i'd first check to see how much fluid it is moving by bleeding them, then maybe take a look at the wheel cylinders. I've had them leak with no visible evidence of fluid anywhere...maybe all that fluid in the booster ate up a seal or the diaphragm?
                If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

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                • #9
                  single brake systems don't have a proportioning valve.

                  My guess is that it's time to do the entire brake system, replace rubber hoses, inspect the metal lines for rust leaks, repair/replace all the wheel cylinders. The only times I've had a brake system that wouldn't bleed was because of leaks. But also make sure the pushrod length on the booster matches the hole in the piston in the master cylinder, and other simple things...
                  My fabulous web page

                  "If it don't go, chrome it!" --Stroker McGurk

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                  • #10
                    Originally posted by squirrel View Post
                    single brake systems don't have a proportioning valve.

                    My guess is that it's time to do the entire brake system, replace rubber hoses, inspect the metal lines for rust leaks, repair/replace all the wheel cylinders. The only times I've had a brake system that wouldn't bleed was because of leaks. But also make sure the pushrod length on the booster matches the hole in the piston in the master cylinder, and other simple things...

                    but he said he got it bled, but it won't actuate the brakes - the only way I can imagine that happening is the internal seal in the piston has already failed. Without back pressure, it's possible to bleed the lines, yet once you close up the bleeder, there's a leak in the seal that allows the fluid to by-pass back into the master cylinder. I just had this issue with the Corvette, 2 brand new master cylinders, neither would actuate the back brakes. In the end, I replaced absolutely everything, then came back to the master cylinder, one cheapo from Amazon, and one cheapo from Speedway - now a Wilwood - and now they work perfect....
                    Last edited by SuperBuickGuy; June 16, 2014, 03:58 PM.
                    Doing it all wrong since 1966

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                    • #11
                      I guess it's a matter of terminology--I don't consider a system to be "bled" unless it actually works.

                      It's easy to test, just plug the line out of the master cylinder, see if you get a solid pedal.
                      My fabulous web page

                      "If it don't go, chrome it!" --Stroker McGurk

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                      • #12
                        he also said there was no fluid on the ground, its not going anywhere. Did you bleed the master cylinder on a bench before installing it? Are you actually getting fluid out when you do open the cylinders? have you taken the bleeder plugs all the way out to see if there is rust stuck in that little hole that allows the fluid to get thru? Rockauto has those bleeders for a few cents, that is if you are not getting any flow to the cylinders.

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                        • #13
                          I am getting flow to the cylinders. I am interested at looking inside the booster again tomorrow to see if this one has leaked into it like the last one did. I could not figure out where the fluid used to go and then I pulled the old master off and the booster was a fluid holding tank, lol.

                          I'll start with Jim's suggestion of blocking the master and trying that. I do know that there is fluid flow from that thing. I lacked motivation last year because of the whole paperwork problem and of course now that I have that squared I want to be bombing around. Will check some basic stuff and report back tomorrow.
                          That which you manifest is before you.

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                          • #14
                            The problem that SBG mentioned with a defective internal seal in the master cylinder will make it so you get some fluid flow out of the master cylinder, but it won't make enough pressure to give you a solid pedal.

                            It's a rare condition, but worth checking. Isolating part of the system and checking it separately is usually a good troubleshooting practice.
                            My fabulous web page

                            "If it don't go, chrome it!" --Stroker McGurk

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                            • #15
                              Jim, if I perform the test you suggest and then pull the master to find that there's bunch of fluid in the booster would that indicate the seal issue?

                              The good news is that the thing ran like a swiss watch during low speed backyard testing today and the emergency brake works great. HA!
                              That which you manifest is before you.

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