I just installed the underdrive crank pulley. The car charges about just under 12 volts when idling. When I rev the engine, the system charges a full charge. I drove the car approx 10 miles and 4 of which were stop and go. The car then died, but would restart. The pulley called for a 59.2 inch belt, but the auto parts store didn't have one, so I tried a 60 inch belt. Could this small of difference have caused the belt to be slipping?

 

Possibly. My March UDs came with the correct belt. JMHO

 

When I ordered mine throung RK Sport I thought I got everything pulleys and belt but only pulleys. So instead of going to the parts house and hopeing to get it right I turned around and ordered the belt from RK Sport. I'd get the correct belt and then see how it does. It will charge on the low side at idle and then rise as you rev it up. I've had underdrive pulleys on both my Camaro's and never had a problem keeping a charge even though I had a huge system in my 94 (Cd changer. crossover, 3 amps and 4 10's)