Astro Van won't go in reverse

I was driving to work and hit a bump in the road. The truck made a clu-clunk and I knew that couldn't be good. But it drove fine to work. When I went to reverse into the parking spot, the truck would not go. It just goes forward. I looked under the hood and under the van and everything is intact. I do not think it is possible for a transmission to just go suddenly like that. So what else could cause it?

What year is the van and whats the mileage on it? Does it rev up when you are in reverse and the gas pedal is depressed?

It is a 1996 and yes, the van appears to be running normal, other than not going in reverse. I will check it out later tonight and have a more detailed reply for you on the "revving up".

yes, it does rev up in reverse. It just doesn't go.