[Mageeacres]

I read a thread where determining rear end ratio by knowing the rpm divided by revolution of the tires = gear ratio.    So I do the math (3100/470=6.59) and the answer is definitely wrong.  So obviously my tachometer is not programmed correctly... (electronic with dip switches) I have a Cat 3208T with an Allison 750 tranny. The PO repowered from a 555 and left the existing radiator and transmission with 11r22.5 tires ... I know lockup in 5th gear is 1:1 and the engine should be kept at about 2800 or below. If I do the math it seems to be reporting about 75% above actual (measured speed with gps). 

    My question is does anyone know what manufacturer and rear end ratio they put in the late 70s early 80s single axle classic coaches build date Oct/79?  Thanks in advance.