Shift problem
Robert are you saying the problem just seems to be 1st and 2nd gear but 2nd to 3rd shift works ok? If so it sounds like the 1-2 shift valve is stuck in the valve body. Might even be a broken spring on the valve. Maybe try putting some trans additive in it such as K&W Trans-X. It might free it up if it's just stuck. If it don't you'll have to drop the pan and valve body and take it apart and give it a good cleaning and or replace the spring.
No not exactly to answer your question. The truck will not go if you just put it in drive. Its trying to start in 3rd gear. You have to put it in 1st gear to start going and manually shift it into second and third. Once in third gear/drive, if you mash tha gas, it will downshift to second automaticly and then back into third automaticly as it should. The problem seems to be that it fails to downshift when you come to a stop.
I have tried this ........
came to a stop in drive/3rd
tried to go forward again
would not go as if still in 3rd gear
manually shifted into first gear
roll forward a few feet in first gear and stopped again
move shifter into drive
again would not go
manually shifted back to first gear
started going but have to shift manually into 2nd and 3rd
drove at 45-50 mph
pressed the gas pedal down untill it downshift automaticly into second
it then shifted automaticly as it should back into third.
Apparently the detent is working and it will shift automaticly if activated by the detent. It just will not downshift properly when I come to a stop. I agree that there must be something stuck in the valve body. I'll try the Trans-X. Gotta admit I'm kinda concerned about adding a cleaner or having to change the fluid in an old tranny not knowing when or if it has been changed as it should have. They usually dont last long once you run new fluid through um for a short while and wash all the fine particles off the clutches. If it goes out completely, I do have at my disposal another tranny in a 87 truck. Same motor in both.
Thanks for your help.
Robert