I've recently gotten my very own mustang (finally) and the previous owner had put in a new gear. He didn't tell me what it was, how do i find out what the gears he put in were?

 

Welcome, and congrats on your mustang. The old school method is to jack up the rear of the car, and use safety stands. With the car in neutral, spin the driveshaft one rotation while noting how many rotation the wheels make.

Example: One rotation of driveshaft = 3 1/2 turns in the wheels, you have 3:55's, approximately.

 

welcome

 

+1 on that. Welcome.

 

Thanks so much for the help everyone!