Hi just bought my first Wagoneer and am new to the board. I just wonder if anyone has experience with this problem.
I have a '76 Wagoneer with a TH400 auto transmission. It will not shift out of 1st while in drive or by putting it in D or 2. When I back out of the driveway it shifts smootly into R and then smoothly into D and seems normal until RPMs build and no shift occurs. The fluid is full and bright red (previous owner swapped the transfer case from a high/low to high range only recently). There are no sounds or vibrations. I drove over 100 miles with no problem when I picked it up. When the problem happened I was cruising on the interstate at around 70mph and started to decelerate like I was coasting and pushed the gas pedal and the engine revved but had no effect on speed. When I slowed to first gear speed it would accelerate but not shift.