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Thread: Mack 18 speed air shift problems

  1. #1

    Mack 18 speed air shift problems

    We have a Mack T 2018 air shift transmission in a Mack RB688S 1993 year model. It has always shifted ok. But lately it will shift on its own. When the driving and in low range, it will shift into high range when you place the gear shift in neutral. Like when stopped at a stop lite. When you come to a stop and put the lever in neutral, with the range selector in low it will shift up to high range on its own, so before you start out you have to flick the range lever down into low then immediately put the gear shift into a gear and start out. Also lately now also the gear splitter wont work in high split. Any advise would be appreciated. Thank You

  2. #2
    Senior Member
    Join Date
    Dec 2015
    Location
    Warwick New York
    Posts
    159
    Sounds like the seals in the range selector are leaking.

  3. #3
    Hi JasonG, and thank you for reply. My mechanical son, resealed the range selector valve, also the piston seals for the back box. He replaced all of the rubber, or "wear" parts.The piston and cylinder was not rusted or scored up. Most of the original seals/orings looked OK also. The shift on its own, problems are still there. Only now there is an added one, the splitter only works in low split. It was working fine before. We are wondering if the issue might be in the hand shifter control head.

  4. #4
    Senior Member
    Join Date
    Dec 2015
    Location
    Warwick New York
    Posts
    159
    Yeah, I should have said the part on the shifter head. They wear out over time.

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