94 Accord no shift when warms up

I just got this accord 94 it's supper clean but when the car warms up the tranny dose not shift . does any one know what might be the cause . I would hate to drop the tranny and put one in and that not fix the problem. might it be some sort of soleniodo. corse I would try changing the tranny oil first. just to see what happens.. thanks in advance Roberto

someone has to know somthing...

need more info. does it slip at all or just stay in 1st? Does it have any kind of whining noise either when it does shift or when its warmed up?