why does my truck turn off and my belt tighten up when i back up?

Answer 1

Don't have a clue!
But from the information that you've given us, as minimal as it is, I will venture a guess.
Since the motor runs in the same direction whether the vehicle is going forward or in reverse, the only thing I could assume is the transmission is having problems. This would be a major problem in reverse though to transmit back through the drivetrain and stall the motor. The belt tightening up doesn't make sense either (especially since I don't know what belt you're talking about!). Since it's driven off the crank shaft pulley, it would have to be a transmission problem which is somehow translating back through the link between transmission/motor and stalling the crank shaft.
If this is a standard/straight shift transmission, then it's plausible because there is a solid mechanical link between the transmission and the motor. However, if it's an automatic, it doesn't make sense at all, because there is no solid link there, only a fluid link (it's called the torque converter).

Good Luck!!!

Answer 2

Hmmm, maybe the end of your seatbelt is hanging out of the door and your backing over it??? Actually need a little more information, does the engine spit, sputter and die or does it quit the same as turning off the key? Are you talking about the lap seatbelt, the shoulder belt or the belt in your britches? Does it happed every time you back up, sometimes, only when going up a steep hill, as soon as you put it in reverse or after you start moving, after backing a few feet or a few miles? (Hey, I've backed that far by necessity.) There's a multitude of reasons why something strange like that could happen, but you first need to narrow it down.