Brakes Locking up Question

Discussion in 'Mack Forum' started by Rich Rolla, Aug 14, 2023.

  1. Rich Rolla

    Rich Rolla Bobtail Member

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    Aug 14, 2023
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    2015 Mack pinnacle cxu612 single axle. I would start the truck build air pressure push in the brake valve and the brakes release. As soon as I put in gear they lock down. I have to pump the brake pedal to get to hem to release again.
     
  2. xsetra

    xsetra Road Train Member

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    Aug 21, 2011
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    Manual transmission? Explain lock down. Does your dash knob pop out?
    Are you sure the brakes are adjusted and releasing. Sounds like cam roll over. IF the cams are rolling over you might end up having them lock up and not release.

    Good luck
     
  3. Rich Rolla

    Rich Rolla Bobtail Member

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    Aug 14, 2023
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    It’s an automatic transmission. Brakes release before I put it in gear. But when I put it in gear I hear a 1 second air release from the brake valve then they are locked down. I put the back window an see the slack adjusters in the lock position. And the knob does not pop out. Brakes are adjusted I’ve have a Michanic to set them but he couldn’t figure out the problem. Just trying to do all I can do before sending it to the shop. When you say cam roll over you referring to the S- cam right. If so I should remove the wheels an check them while someone is applying the he brakes. Thanks for the info.
     
  4. xsetra

    xsetra Road Train Member

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    Aug 21, 2011
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    Yes the S-cam. What happens is the brake shoes and drum wear down to the point, when applying the brakes, the S-cam rotates to a point it gets wedged and won't release.
     
  5. Rich Rolla

    Rich Rolla Bobtail Member

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    Aug 14, 2023
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    Sounds good thanks for the info
     
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