I recently rebuilt my 1946 GMC 1/2 ton three speed trans. Replaced input shaft, counter shaft, synchro rings among other items. The trans worked great for fifty miles then while driving it wouldn't go into second no matter what I tried. Drove the truck home using 1st and 3rd, no problems. Opened up the top and I can't see any damage but it still won't shift into 2nd. It's like the spring and ball on the shifter shaft won't let the shift fork move the synchro drum toward 2nd gear. Does anyone have an idea what happened? I thought I'd check with the forum before pulling the trans. I am hesitant to try and force it. I think pre 68 Dave might have an idea of what is wrong but I'm looking for any thoughts

Thanks, Dave