brake question... Steve Chin?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Thumper, Aug 18, 2001.

  1. Thumper

    Thumper 1/2 ton status

    Feb 17, 2000
    Likes Received:
    Alberta Canada
    This is after my disc swap on the rear.
    I am still getting no pressure to the rear calipers. There isnt any air in the system, I bled
    them at the main T, then at the flex line to the caliper, then at the bleed screw. The
    little pin on the proportioning valve pops out every time I press the brake pedal. BTW, all
    the above bleeding was done with the little pin held in by a clamp. When I remove the
    clamp, it still pops out. The 'BRAKE' light is on steady, and the pedal is really crappy
    feeling. Does this mean that the valve is shot? The front brakes work good, and when I
    bled them, it felt normal... ie. the pedal would dump to the floor when I open the
    bleeder, but when I open the rear bleeder, it doesnt dump to the floor. It seems the
    problem is that its shutting down the rear brakes, but isnt the little pin on the valve
    supposed to be a manual bypass to get the back to work? I am lost and frustrated. Does
    anyone have any ideas?
    Also, to the guys that have swapped to discs before... did you have to change the
    master cylinder or the prop valve for them to work??

    Any help is appreciated.


    <font color=blue>Thumper
    85 Fullsize Jimmy
    <font color=red>Aint Skeered!! </font color=red>
  2. POFF

    POFF 1/2 ton status

    Aug 13, 2001
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    San Diego, CA
    I don't have rear discs but I had the same problem when I converted to front discs. I got no fluid out of the rear cylinders and the pin on the prop was pushed all the way out. I had too much air in the front lines. The prop valve thought it need to apply more pressure to the front brakes. I re-bled the front and it solved my problem. Worth a try?

    '70 K-20 San Diego, CA
  3. Steve_Chin

    Steve_Chin 1/2 ton status

    Mar 6, 2001
    Likes Received:
    Foster City, CA, USA
    Sounde to me like you have a combination valve for a disc/drum system on your truck. I don't know if that is the problem or not, but I purposely used a proportioning valve that was designed for a car with 4 wheel disc and had similar weight proportions to the Blazer so that it'd work.

    Normally, a combination valve will give you a little bit of a problem wiht the rear brakes dragging. I would think that you either need to adjust the parking brake or that the ratchets in the pistons for the parking brake are broken/seized.

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