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81 chev. G10 van

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  • June 5, 2014 at 4:22 pm #597325
    GlennGlenn
    Participant

      I replaced front and rear brakes,and one leaking wheel cylinder. Bleed system with vacuum pump several times,and I am getting no more air out. However when I get on brakes hard pedal feels spongy at first,and rear wheels skid.thinking maybe M/C or porportioning valve,and maybe still some air in front system.can’t figure it out . Need sum advice.

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    • June 5, 2014 at 5:45 pm #597331
      dandan
      Moderator

        the proportioning valve does limit pressure but under instances where there is very hard breaking…

        did you during trying too bleed your system run the master cylinder out of fluid? if you have ran it out of fluid air could be trapped in the master cylinder.

        check this out also
        http://www.ericthecarguy.com/faq/solving-brake-problems?start=8#BleedingtheBrakeSystem

        June 6, 2014 at 12:40 am #597432
        EricTheCarGuy 1EricTheCarGuy
        Keymaster

          The rear brake adjustment might also be coming into play here. How the rear brakes are adjusted has a lot to do with how good or bad the pedal feels. If too much fluid bled out when you replaced the wheel cylinder it might have introduced more air into the system elsewhere. You may need to bleed all 4 wheels if you haven’t already. More information on solving brake issues here.

          http://www.ericthecarguy.com/faq/solving-brake-problems

          Good luck and keep us posted.

          June 10, 2014 at 6:08 am #598287
          GlennGlenn
          Participant

            Last weekend I bled m/c and front brakes. I got some air from right front brakes ,not sure about m/c,the little tubes might have had some air trapped in tube. Brakes seem better ,but rear still skid first. I backed off rear adjusters today after wk.. Pedal is lower ,brakes aren’t any better . Think I’ll back up several times to readjust to where they were. Think’in I’ll feel brake hoses while friend pumps brakes to see if I can detect any bulging. The pedal seems firmer than I have felt air in the past. Can a porportioning valve be cleaned ,there kind’a pricy?

            June 11, 2014 at 1:15 am #598453
            EricTheCarGuy 1EricTheCarGuy
            Keymaster

              Often if the rears are locking up it’s the friction material. AS for the proportioning valve, In order to bleed some old GM systems you need to pull the pin up in the center of the valve. It’s usually located in the front of the valve under a rubber plug. They actually make a special tool for this.

              http://www.grainger.com/product/2TVH9?gclid=CJj-49Kc8L4CFckWMgodVxoAGg&cm_mmc=PPC:GooglePLA-_-Fleet%20and%20Vehicle%20Maintenance-_-Automotive%20Mechanical-_-2TVH9&ci_src=17588969&ci_sku=2TVH9&ef_id=U5c3tAAAAfooP@xE:20140610211251:s

              If you have that type of proportioning valve, you may need to use that tool to bleed the system properly.

              Keep us posted.

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