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Thread: 83 GMC dropping out of gear

  1. #1
    Join Date
    Jul 2009

    Default 83 GMC dropping out of gear

    My 83 GMC Serra 3/4 ton pickup drops out of gear when the engine warms up while driving. I can get it back into gear by shifting into neutral then back into drive. This is an TH400 automatic transmission. The shifter handle does not disengage it stays in the proper position in drive. I had the transmission serviced just over a year ago. New filter, fluids and seals. This vehicle is NOT driven every day just occasionally. There has only been 700 km put on it since transmission filter changed. Before the work there had been no issues with the transmission. Oh yes the transmission was removed to replace the flywheel/drive plate.Any ideas as to the cause of it dropping out of gear?

  2. #2
    Join Date
    Jan 2007


    Hi GrandAm03,

    Check the fluid level to make sure it's ok, and also check the shift linkage adjustment. Beyond that, you'd be dealing with an internal problem, most likely something to do with the valve body. Diagnosis with a pressure gauge would be required at that point.

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