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brake problems

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by 69K5, May 7, 2002.

  1. 69K5

    69K5 1/2 ton status

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    I changed out my master cylinder, and now my breaks wont work. with the truck off they will build up pressure, but as soona s you crank it it goes all the way to the floor. i rebled all the lines 6 times starting with the farthest back. there is no air in the lines. whats wrong. the wheel cylinders booster and master are all new. could this be a dud master i got. i bench bled it with no problem. the master is a remanufactured. any ideas before i go swap this thing out?

    my 69 doesnt have a pin on the proportionin valve. its just ablock that splits the fluid. i looke from one end of the line to the other and no pin.


    i got to thinking. it works when off but not when on. well i undid the vaccum and cranked her up and they worked. so who votes for the booster. i have to go to work now, but will try it when i get home.
    thanks

    nathan
     
  2. Triaged

    Triaged 1/2 ton status

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    It is not the booster. If it was not working the peddle would be hard not soft.

    The button that you push is on the prop valve at the front. It has a rubber cap over it. I jamed a stick up against the rad. support to hold it in while I blead my brakes. I have never found it to make much of a difference.

    IMO you have 2 options.
    1) Have a shop "power bleed" it (some people hear have had good luck with that).
    2) Replace the master (again)

    You might also want to make sure you didn't make a "stupid" mistake like:
    Putting the calipers on the wrong side so the bleeders point down insted of up
    Not having the rear shoes adjusted
    and stuff like that.

    Do you have anyone around that can give it a once over to check it out? Sometimes a fresh perspective helps alot!
     
  3. 69K5

    69K5 1/2 ton status

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    i dont have disc brakes. i dont think they came on 69's. i have 4 wheel drum. i might have misput that in my post. i have a friend that could powerbleed them. i finally got it to where i think its safe to leave the driveway. i found a rubber plunger that had fallen out of the pushrod place in the booster. this stopped the flooring with it cranked, but theey still arent quite up to par. i will take them to my friend and have him give em a powerbleed. i think i will hold off on replacing the master again, until i get a second opinion like you said. i already checked the wheels and have the right shoe in the right place (primary, secondary) My wife had me check that first she knows i get in a hurry and forget stuff. shes gettin pretty good at the mechanicin part. now if she'll just sell her hyuandai and get a blazer. ha ha

    thanks for all the help

    nathan
     
  4. ntaj*ep

    ntaj*ep 1/2 ton status

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    If the master and booster came apart I think maybe the master cylinder push rod may not be adjusted correctly. that may explane the pedal sinking. If its not traviling far enough to fully blead the system iin the conventional manner. A power booster in a 4 wheel drum truck? Is this an option? I have a '70 with 4 wheel drums and no booster. Did you do this swap?
     
  5. 69K5

    69K5 1/2 ton status

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    I dont know if the booster was an option or not. The one on mine was an original. whenever I swapped it the part number we ran was an oem. I have all the original paperwork from the dealer. i will dig it oiut and see if it came on the options list. your right the rod was not far enough out. we adjusted it and now it works. I have a wheel cylinder leaking now(suprise?) I will fix that tommorow. thanks for the help.

    nathan
     
  6. Steve_Chin

    Steve_Chin 1/2 ton status

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    If your parts are new, then rule out what I'm writing next, but if they're rebuilt, read on. I know a *lot* of people who have had nothing but trouble with rebuilt master cylinders. I took a couple of them apart and found a lot of deep pitting in them, which would lead to internal (and maybe external) leakage, causing a spongy pedal.
     
  7. 69K5

    69K5 1/2 ton status

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    the master is rebuilt. i got it because the rebuild kit was 12 dollars more. everything else is new. the brakes stop now but they arent where i would like them to be. they dont fade, but if i had to stop fast i couldnt. i just start slowing down early. they pull really hard to the passsengers side. i just need to replace the drums. they have seen better days. maybe i am just spoiled by disc brakes. cant decide whether to yank the master or not.

    thanks

    nathan
     
  8. 70jimmy

    70jimmy 3/4 ton status Premium Member GMOTM Winner

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    I have 4 wheel power drum on mine. I have never messed with the booster but replaced all wheel cylinders, cleaned all parts, all new shoes, turned all drums, bled the system. It worked pretty well for a while but steadily over time about 18 months developed nasty pull to left. jab brakes once to switch to left lane and twice to turn left. Not quite that bad but close.

    I am planning on switching to 4 wheel disk someday. Post what ya find out cuase it probably will help me too.

    A mechanic friend of mine said you have to keep on top of adjusting them like once a month or so for them to work good. Water crossings probably dont help either.
     
  9. 69K5

    69K5 1/2 ton status

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    Mine already have a really bad pull to the right. which probably means i need new drums.I didmt get them turned b/c i ran out of money. mace sure you didnt get any grease or break fluid on your shoes. that will make them pull to one side.I want to switch to disk brakes. as soon as i find a donor truck they are gone. I will let you know what i find out.

    do you know if you could use the disc brakes off a 2 wheel drive truck somehow?

    thanks

    nathan
     
  10. 69K5

    69K5 1/2 ton status

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    I checked and it was factory installed. option # 4J80SE

    If you wanted to install one I dont see how it would be that hard. should just have to move stuff out. are youy sure yours wasnt taken off? Look in your glove box and see if it was on it.

    nathan
     

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