1972 C50 (2 Ton) Brake petal has to be pumped to get a high petal

Discussion in 'Chevy Truck Forum' started by ZO6Vert, Mar 14, 2012.

  1. ZO6Vert

    ZO6Vert Member

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    1972 C50 218" wheel base that I converted into a pickup by shorting the frame (a lot)

    After replacing a few lines and all eight of the cylinders (it has two per backing plate) I have to pump the petal to get it high. The shoes are adjusted so that it is hard to turn them. So I don't think the shoes are to far away from the drum. I have bled it many times and still no change. I have no air when I bleed them. It has a master cylinder and a cylinder at the booster (under the cab)that I have bled as well but have not replaced
    I am out of ideas of what the issue could be. The petal stays hard as long as you keep pressure on it. If you take you foot off for 30 seconds you have to pump the petal again to have a high petal.

    (history)The truck sat for over a year when I first got it and when I drove for the first time I only had rear brakes. There was a leaky line and one that looked suspect so I replaced them all, I had to replace the one going to the back anyway when I shorted the frame. The fronts have bleeders in each cylinder but the backs only have one in the top cylinder.

    Any ideas or comments are welcome.

    thanks
    Dave
     
  2. chevychase

    chevychase Senior Moderator Staff Member

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    You still have air in system..if you pump up and holds till you let off means air.
    Start at the passenger rear..then driver rear..then pass. front then onto driver front.
    When you bleed put something at floor board as not let pedal go to far..maybe a piece of 2x4.
    May have to bled a pint through each wheel. Could gravity some out loosen bleeders ..let it drain ..keeping eye on fluid not to let run dry.
     
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  3. ZO6Vert

    ZO6Vert Member

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    I will try it again, but I always thought that a mushy petal was air, mine is hard. But Ill try anything! Thanks for the tip!
    thanks
    Dave
     
  4. chevychase

    chevychase Senior Moderator Staff Member

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    You said took foot off pedal.. had to pump to get good pedal again.
     
  5. 88fivespd

    88fivespd Full Member

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    It's real tricky to get the brake shoes adjusted up tight enough without getting them too tight. You certainly don't want to get them over tight as they will heat up in a hurry. What you described in the second paragraph of your original post could be either air in the lines or the shoes not adjusted tight enough. I have a couple old Chevy two ton trucks 1958 and 1963 so I have more than a little experience trying to get the pedal to not go down too far. How far does the pedal go down the first time you push it?
     
  6. ZO6Vert

    ZO6Vert Member

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    All the way to the floor the first time, 2nd time about half or more, third time full hard petal. This is with the truck running.
    thanks for your assistance
    Dave
     
  7. ZO6Vert

    ZO6Vert Member

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    Well thanks to all who replied and after bleeding the brakes no less then 20 times per wheel. I have brakes!!!! I keep bleeding them and then finally I started to get some really small bubbles and then a streams of foamy bubbles came. They got less and less as the bleeding when on and on. I don't know where the air was hiding but I guess I don't care now.
    thanks again
    Dave
     
  8. chevychase

    chevychase Senior Moderator Staff Member

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    Glad you got it fixed zo6vert..and posting back.
     
  9. c50

    c50 New Member

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    Zo6Vert,
    I have a 1972 C50 grain truck and I have had the same problem that you have had with your truck. I have replaced the master cylinder, all 8 wheel cylinders, installed new brake drums, new shoes, replaced all brake adjusters, and a lot of other stuff. After all this and a lot of bleeding with a pressure bleeder the pedal would go to the floor with the first push then halfway down on the second push (but the pedal was hard on the second push). I have struggled with this thing for about a year...the truck had the same problem when I bought it. Last week I spent about a half day trying to figure out the problem by using the web and looking at my GM manuals. I found out that my truck has optional brakes (6 inch wide rear brake shoes instead of 4 inch, and 3 inch wide front brake shoes instead of 2 1/2 inch). The 1971 GM Chassis Overhaul Manual Supplement, 40-60 Series Trucks specifications (Specifications page 4, brakes) says that the C50 has a standard master cylinder piston diameter of 1 1/2 inches and an optional master cylinder piston diameter of 1 3/4 inches.

    I went to Oreilly's auto parts and asked for a master cylinder for the C50 and they looked it up and gave me the first one on the list (Cardone 10-57579, 1 1/2 inch piston) instead of the Cardone 10-57577 (1 3/4 inch piston). I installed the 1 3/4 inch master cylinder and...Problem solved! Actually, I found out just before I installed the 1 3/4 inch piston cylinder that the pedal actually did not go all the way to the floor with the 1 1/2 inch master cylinder...it went to less than 1/2 inch of the floor! With the 1 3/4 inch master cylinder the pedal only goes down about 2 inches.

    The 1 1/2 inch master cylinder just did not provide the volume of fluid that the larger wheel cylinder required with only one push! I hope this is helpful to someone!
     
  10. Oldmech

    Oldmech Full Member

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    bah... didnt log on in time to help, but CC handled it... With all those wheel cylinders they ARE a pain to bleed. Its easiest to use a bleeder ball to save the leg of whoever is running the brake pedal. When your SURE you have bled everything out WELL, spend the exact same amount of time continuing to bleed it all over again :)
     

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