GM 6 speed trans problems

Discussion in 'Talkback' started by rsssc, Jan 2, 2010.

  1. rsssc

    rsssc New Member

    I have a 98 Monaco 40 ft. 350 hp Cummings that is 1 month old to me. On a trip south, after 2500 miles, the transmisson down shifted to 4th and would not shift up or down, N or Rev. I limped to a dealer where the tech could not get his computer to read the trans codes or find the problem. He then shut down the motor and it went to N and could be restarted but the trans selector stayed in N. He then shut down and replaces the trans selector box with a used box he had in his tool box. I test drove and all was well, and they let me keep the spair box to get home, 700 miles. We made it home to MN and the weather turned cold, 0 to -15 at nights. I had to move the RV 4 days after we got home and after I got it to start it wound not go into any gear. I switched the shift comtrol box to the orginal one and I backed up once and went into D then to N and now it will not go into any gear. I disconnedted the chassia battery to reset the unit but still no getting to R or D. I tried the borrowed box with no luck.

    Please help me with info on how to trouble shoot and fix. The throttle does not work either. Thank You RB
  2. LEN

    LEN Senior Member

    Re: GM 6 speed trans problems

    First of all you have an Allison Transmission.
    Repost this in "Geneal RVing" section about 2/3 the way down the page is "Allison Transmission Questions". We have two people in the know that visit that page and can comment. Sounds to me like a engine speed sensor, but just from what I have retained reading about the Allison Transmission.

  3. dbarton291

    dbarton291 Senior Member

    RE: GM 6 speed trans problems

    The sequence of events you have described is full of a lot of potential variables, so doesn't lend itself well to a fairly cut and dry troubleshooting sequence by itself. The cold temperature could be inhibiting operation in MN, it could be sensors, it could be the controller itself. Without any trouble code information, transmission or engine, it's difficult to tell you where to begin.

    I would recommend going to and click on the service locator. Find an authorized Allison service outlet in your area to help you out. I know Interstate companies operates quite a number of authorized Allison distributor locations in Minnesota. They are at

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