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Help needed with new brakes D60/14B (Long)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazer79, Mar 6, 2003.

  1. Blazer79

    Blazer79 1/2 ton status

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    First of all, I'd like to point out that I spent two days reading the search results for brake problems all the way back to 2000

    I just finished installing a D60F and 14Bolt. I noticed that my brake lines where dripping mud, not brake fluid, so I decided to replace everything I could. I got new master cylinder, new steel lines new longer flexible rubber lines, new rear wheel cylinders. The only parts that were nor replaced, but thoroughly cleaned where the D60 calipers and the proportioning valve.

    I mounted the master cylinder on the truck and bench bled it there. I installed two clear pieces of hose and put the other end in the reservoirs. I had a friend slowly pump the pedal until no more bubbles were visible. Is this the proper method? I noticed that the instructions sheet mentioned that the piston should get harder to push when there was no air, but my friend never noticed any change.

    I then installed the new lines to the MC and proceeded to bleed the rest of the system. The fronts were perfect, high pressure when opening the bleeder screws, but the rears just poured, no pressure. The pedal always goes easily to the floor too.

    I removed the line that goes from the rear of the MC to the Prop Valve because I found it was kinked. I fixed that but now I got air into the system again. Benck bled the MC again, Installed the line back, now I get even less flow to the rears. /forums/images/graemlins/confused.gif

    I then did a messy check. If I disconnect the rear output of the MC and put my finger and have a friend slightly press the pedal, the pressure blows my finger away (good). Now if I install the line to the rear of the MC and put my finger on its end, I got little pressure. /forums/images/graemlins/confused.gif I rechecked this line for more kinks but everything is smooth. I had my friend slowly pump the pedal while I had my finger on its end acting like a bleeder (open to release fluid, closed when he was lifting the pedal). This removed the air and increased pressure somewhat, but not enough to blow my finger, much less to make the rears work.

    QUESTIONS:

    1) Why is there pressure at the MC and little pressure at the end of the first line? There are no obstructions. I can blow freely with my mouth.

    2) What are the symptoms of an improperly bench bled MC?

    3) What are the symptoms of a bad MC?

    /forums/images/graemlins/ears.gif My Blazer wil appreciate any help that prevents me from dropping her off a cliff /forums/images/graemlins/mad.gif
     
  2. Blazer79

    Blazer79 1/2 ton status

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  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    There is a button or swith on the end of the proportioning valve, try to push it in to re-set the proportioning valve and hopefully this will cure your problem.
     
  4. K5thatShmobs

    K5thatShmobs 1/2 ton status

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    Have you checked the pressures of the front and rear fittings on the the MC itself? Unscrew the fittings from the side of the MC, and press the pedal... If youre not getting good pressure from those themselves, it can only be one of two things:

    -You need to re-bleed the MC
    -The MC is defective

    If youre getting good and roughly equal pressure from both of those, your problem lies within the proportioning valve. Theres a little sliding valve called the switch piston in the middle of your PV that slides back and forth "proportioning" pressure between the front and rears. What usually happens when doing brake work is the switch piston (see below) will constantly slide the right, blocking pressure to the rears.

    [​IMG]


    Apparently pushing the "button" on the left side of the PV will relieve pressure in the chamber that goes to the fronts, sliding the switch piston back to center, but it didnt work for me. I disassembled the PV and gutted the switch piston itself. That gave me great pressure everywhere, but its not a recommended method.
     
  5. K5thatShmobs

    K5thatShmobs 1/2 ton status

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    Oh yeah, and if you do try and use the button on the PV to reset it, you have to have a buddy pressing on the pedal so that the system has enough pressure to slide the piston to center.
     

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