BroncoII4x4.com

I have an '89 Bronco II, 4X4, auto trans. When the vehicle is cold, no matter the outside temp, it will not shift out of first gear. I have to monkey with the acceleration and it will eventually shift. Normally takes less than 2-3 minutes to get it to shift. Warming the truck makes no difference. Once it shifts I have no problems with it from then on. No slippage whatsoever. Any ideas? I plan to change the filter and fluid and also the vacuum modulator, if equipped. Clueless beyond that. Thanks!

change the fluid and filter ta start

Sounds like a sticking valve in the valve body. Like Ranger Dave said, change the oil & filter. There are a lot of fluids on the market to help with the sticky valve problem if that's the case, but do your research!
Some are good, and some not so good.

it could be the main pressure valve because it is a aluminum valve and aluminum valve body with steel sleeve between the too. it get little rought and the metal expands at diffent rates and problem sticks close when you shut off the truck off when the tranny is hot