9 speed Eaton won't shift into low range?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by 704mover, Dec 8, 2019.

  1. 704mover

    704mover Bobtail Member

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    Mar 8, 2018
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    9 SPD won't shift into low range, high does work. I checked the air switch on the shift knob, replaced the air switch box up high on the driver's side of the transmission. Is there a o ring or diaphragm inside the 4 bolt cover on the rear of the transmission where the two air lines hook up? Someone suggested a snap ring off on the shift rail or fork? Help? Thanks
     
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  3. bjrc

    bjrc Light Load Member

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    Sep 14, 2018
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    There is a piston with an o ring inside the 4 bolt cover. Remove both of the hoses at the 4 bolt cover and have someone toggle the hi lo switch on the shifter while trans is in neutral. You should have air from one hose while in low range and the other in hi range. If air is working properly piston could be frozen or other internal problems.
     
  4. 704mover

    704mover Bobtail Member

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    Mar 8, 2018
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    Thanks, it's raining here and I cant move my truck with only high range into the shop. I barely got it home, it hung up at the stop sign below the shop coming in. I had to really slip the clutch to get it going with a load behind it. When it dries up I'll pull that cover and go from there. Maybe it's just a torn o ring. Thanks a lot.
     
  5. Chubby Fly

    Chubby Fly Medium Load Member

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    Nov 25, 2019
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    Check slave valve to see if functioning first. Located on side of trans on the forward side drivers side.
    If not that then you have a bigger issue. Broken snap ring on high low shift fork. Or it came off
     
  6. Robmac

    Robmac Bobtail Member

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    Dec 10, 2019
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  7. Robmac

    Robmac Bobtail Member

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    Dec 10, 2019
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    My 9 speed won't go into high range low range works just fine any idea's
     
  8. Robmac

    Robmac Bobtail Member

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    Dec 10, 2019
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  9. Robmac

    Robmac Bobtail Member

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    Dec 10, 2019
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    I have been trying find a picture of the two air shift solenoids on the top and back of trans
     
  10. bjrc

    bjrc Light Load Member

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    Sep 14, 2018
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    Test for air at the two bigger hoses. See post #2. There are no solenoids just a slave valve on the left side of transmission that directs air to piston when shifter goes to the neutral position, ( allows you to preselect low and hi range) and a pressure regulator and filter that lowers air pressure to about 60 psi.
     
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