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Bad brake booster?

Discussion in '6.9L IH & 7.3L IDI Diesels' started by saburai, Oct 12, 2019 at 2:05 PM.

  1. saburai

    saburai Supporting Member Supporting Member

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    Will a faulty or leaking vacuum booster cause a sinking pedal?
     
  2. 79jasper

    79jasper Chickenhawk

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    Sinking pedal is usually rears out of adjustment.

    Sent from my SM-N960U using Tapatalk
     
  3. saburai

    saburai Supporting Member Supporting Member

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    Just had the rears apart to check. Shoes are almost brand new, .06 thinner than new NAPA fleet shoes. Adjustment is fine. Gotta be the master, right?
     
  4. 79jasper

    79jasper Chickenhawk

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    Pretty much.
    If you pump them a bit and still bleeds down, I would say master.
    Have you bled it all pretty good?

    Sent from my SM-N960U using Tapatalk
     
    saburai and RetiringColt like this.
  5. saburai

    saburai Supporting Member Supporting Member

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    Yes, I flushed nearly a gallon through the system until it ran clear. The master and reservoir look comparatively new so I didn't suspect it. I did eliminate the RABS valve since that's what I had first thought was the cause of the sinking pedal. I've gone through the whole system, the master is the only thing that's left...
     
  6. Randy Bush

    Randy Bush Full Access Member

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    Although have not done it yet on mine, I think the real way to test the MC is to find fittings to plug off the mc and see if it is bypassing or not. Have done a lot on mine and still have the problem.
     
  7. saburai

    saburai Supporting Member Supporting Member

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    Did you eliminate the RABS?
     
  8. Randy Bush

    Randy Bush Full Access Member

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    Nope , put a good one off a dead truck I have, same problem.
     
  9. saburai

    saburai Supporting Member Supporting Member

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    So if I understand, you replaced the MC, know that the RABS valve is good and have no leaks. In my mind, if you are sure about the RABS valve, you've got a bad master...
     

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