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1-ton Master Cylinder causing brakes to drag???

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by KrebsATM02, Feb 12, 2003.

  1. KrebsATM02

    KrebsATM02 1/2 ton status

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    I just got done rebuilding my whole front axle, new seals, bearings, ball joints, and calipers. I also put on a 1-ton master cylinder i bought from my buddy. because my buddy bought it for his but wrecked it. He only had it on for a month and i need a new one so i just bought it from him. My problem is that the calipers are sticking, I just went for a test drive around the block and when i got back the front brakes were smoking. The system isn't bled very well but i don't think that would cause the calipers to drag. What do you all think??? Thanks - Doug
     
  2. imiceman44

    imiceman44 1 ton status

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    Check the length of the rod, they should have similar lengths or else if it's longer than the stock one you will have the brakes applied slightly all the time.
     
  3. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    I agree with iceman, check the pushrod that goes between the power booster and the master cylinder, or whatever rod it is that engages the master cylinder could be the wrong length.

    Bleed the brakes.
    Put the truck up on jacks and spin the front tires by hand. get someone to pump up the brakes.
    relase the brakes and try to spin them some more... It'll be easier to figure out exactly whats going on.
     
  4. BobK

    BobK 1/2 ton status

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    yup,what they said. /forums/images/graemlins/grin.gif
     
  5. Sparky87k5

    Sparky87k5 1/2 ton status

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    What 1 ton truck model was the MC for? I'm using one that was for a 91 1 ton truck with 4 wheel discs and have no problems. If yours isn't designed for disc/discs, you may have to remove the little residual ( I believe thats the name) valve in the MC. Keeps pressure on a little for drum brakes and can cause dragging on discs. I had to do this when I put 4 wheel discs on my son's Bronco.
     
  6. blazen_md

    blazen_md 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    I had to do this when I put 4 wheel discs on my son's Bronco.

    [/ QUOTE ]
    You let your son buy a bronco mmmmmm thas not good parenting!! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
     
  7. Derf00

    Derf00 1/2 ton status

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    You need to see that Bronco! /forums/images/graemlins/thumb.gif
     
  8. Sparky87k5

    Sparky87k5 1/2 ton status

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    Well, I actually built the Bronco (68) before I got the K5. At the time I owned a Suburban powered by a 513 Caddy and hadn't thought about a K5 for him. Having raced F**ds for a number of years, I wanted something with F**d power as I had a lot of spare engine parts. Did a complete frame off restoration and modified heavily for todays world. In process right now of a NV3550 swap inplace of the stock 3 speed manual.
     
  9. the professor

    the professor 1/2 ton status

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    The short answer is NO the 1 ton master cylinder will not cause the front brakes to drag (unless it had drum brakes on the front)
    --
    How things work:

    Disk brakes, have block seals, these seals serve two purposes, to seal the piston AND to retract the piston a few thousands of an inch, to prevent drag....in any case, there is no spring on the piston, and the seals, seal equaly both ways

    Drum brakes have "cup pistons", and the shoes are retracted with a spring...(there is a small spring on the piston but it is not important for this)..the shoes do not "retract" the pistons all the way, and it gets worse as the shoes wear...also, most drum brakes are "self-energizing", they rotate into wheel rotation, and the "lead-shoe" aplies the "trailing-shoe"...

    Result, lots of motion at the wheel cylinders...
    --
    Cup-piston seals, REQUIRE a small amount of pressure, to prevent air from working its way past the piston
    --
    Why all this bull****...well, the front brake piston part of the master cylinder, is usual larger in area than the rear, and it differed in one very important area..

    Disk brakes DO NOT use a "residual pressure valve" and most/many drum brakes DO..

    The residual pressure valve, is a small valve located in the ouput port of the master cyl, to maintain pressure on the drum brakes...

    Not all GM trucks use a residual pressure valve, because the "head of pressure" from the high mounted master cyl is enought to prevent air from getting into the rear brakes...
    ----
    ====
    That said, the one for a 1 ton might...AND it might also have the front and rear brake pistons reversed front to rear,......so you might have hooked the lines up backwards for that master cylinder..resulting in the brakes staying applied... . /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif

    ==================================
    It is also possible that there is a problem with the "proportioning valve" located on the front x-member...
    There is a special bleeding procedure for this, ...take the rubber cap off, and hold the pin in while bleeding and they should be "suction bleed" from the rear..first

    The "proportioning valve" on GM trucks, applies the REAR brakes FIRST, then AFTER THE REAR BRAKES ARE APPLIED applies the front brakes....

    I have seen problems with this valve, that won't let the front brakes release..

    ======================================================

    Test:
    jack the truck up, apply the brakes hard, try and rotate the wheels, and see if they drag..(some is normal)..

    If no drag or little drag, you might have air in the rear brakes, or the MC may be connected in reverse (different sized pistons)

    IF the drag is bad, ...break the bleeder loose...if the pads retract immediately, it is problably a problem with the proportioning valve, reversed lines or bad calipers..

    If it still drags with the bleeder open, the problem may be in you calipers...try and pry the pads back from the disk..if the drag stops, it is most surely the calipers
    .

    Next, repeat this, only crack the line loose at the master cyl..if they retract easily, switch the lines..If they don't its probably the proportioning valve

    /forums/images/graemlins/truck.gif /forums/images/graemlins/cool.gif
     
  10. Sparky87k5

    Sparky87k5 1/2 ton status

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    I learned more about brakes from that post then I ever knew before. Thanks for the edumacation, I really needed that. /forums/images/graemlins/thumb.gif "you are the man" /forums/images/graemlins/smile.gif
     
  11. the professor

    the professor 1/2 ton status

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    I can get a little long winded..thats where I got the nickname "the professor"
    -- /forums/images/graemlins/blush.gif
    "reread my post..major error..left out under "test", "jack up and apply the brakes THEN RELEASE THE BRAKES.." would definately would hope to have alot of drag otherwise..
    -- /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
     
  12. KrebsATM02

    KrebsATM02 1/2 ton status

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    Well i wish i would have read your post before i took a shower and put everything up!!! If i can't all that to work i wasjust going to get a new 1/2 ton master cylinder and booster, but the more i think about it, i might just do hydro boost. This is really starting to frustrate me!!!! This is my only car and i have been without it for 2 weeks!! Thank god the bus can get me to campus and back. Let me know what you think of the hyrdo boost?

    Also wanted to give you background on the rest of the brakes and what i did today. I have a 14-bolt on the rear, 3/4 ton front (but that doesn't change anything from 1/2 brakes). Warrantied the master cylinder out yesterday, so it is brand new. Switched the old brake booster back on, neither of those helped. So then i got new caliper for one side and it still drags. There can't be any air in the system, i have bled it so much it is rediculous.

    After all that the front still drags and it doesn't stop for [censored]. The rear resevoir is larger, same as on my old master cylinder.

    Thanks - Doug
     
  13. KrebsATM02

    KrebsATM02 1/2 ton status

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    Ok, I bought a new 1/2 master cylinder and booster tonight, going to put that on in the morning. I also got a proportioning valve from the junk yard today. It was out of a older blazer but has all the same connections as mine. The only thing that is different is mine has square edges and the older one has rounded edges. Anyone know if they are internally different???? Please help me solve my braking problems!!! /forums/images/graemlins/1zhelp.gif
     

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