Jack one rear wheel off the ground, leave the other on the ground. Chalk mark the tire and one on the floor. Mark the drive shaft and rear end. Turn the tire 2 complete turns and count the no. of turns the drive shaft turns. If the drive shaft turns a wisker over 4 turns it's a 4:10 if it turns close to 3 and 3/4 it's a 3:71 ect. Walt