so i got my new car not too long ago and it had no alternator belt on it, the guy gave me a new one with the car. the one he gave me was too long so i had to buy a shorter one. well yesterday i heard a noise and looked and both belts came off. i found the alt belt on the side of the road but the powersteering one was gone. so i fixed it and bought a new power steer belt and then today driving the alternator belt came off. im assuming it broke because the powersteering belr is still on the car. i have an unadorthadox underdrive pully and thats the only aftermarket thing concerning the belt drive. any suggestions why it keeps breaking?

 

you sure the one he gave you was new? other than that it might be overtensioned, its easy to break belts like that...also the crank pulley could be slightly out of alignment, also you're assuming it broke, it could have been under tensioned and slipped off at higher RPM