96 transmission

I got in my 96 explorer this morning put it in reverse,heard a pop and no reverse, but all other gears work on the automatic transmission , any suggestions would be greatly appreciated
thank you , dude

I got in my 96 explorer this morning put it in reverse,heard a pop and no reverse, but all other gears work on the automatic transmission , any suggestions would be greatly appreciated
thank you , dude just me again with more info. i bought the exp. used with 100000mi at 140000 i had the tans. flushed, i dont know if this could have caused it, ive put 5000mi on since, dont know if it could be something minor or not? any thoughts thanks dude

p.s it makes a nice work car