My shift handle wont go into R or D or P it just goes past them!?

I was in park and went to put my truck Ford 150 1992 4.9 6 cyl automatic into D but the shift handle acted like somthing broke it was not a hard like a bolt gave way it was like a cable broke. My shifter just goes back a forth without it stoping, it does not go into gear. I got under the truck I could put my hand on the thing a cable goes to on the tran I pulled on it and I got it to go into R and it would go back that is how I got it back down the lane.It will kind of go into park a nuff to keep it from rolling but I can't get my keys out. When I was under it I did not have the or was not able to pull that shift thing on the tran to go into drive.What could this be ? What broke to make my shifter go back and forth???