MY 1969 PETE ON YOUR STEPDECK? SHOT IN THE DARK!!

The drive shaft speed is also limited by the rearend ratio. A driveshaft turning a set of 4:30's running at 60 mph will turn the same speed regardless of what s turning my it. If your cruising down the road at 60 mph in direct and you flip the button on the side of the shifter into overdrive then resume cruise at the same 60 mph your driveshaft speed did not change because your rearend ratio didn't change. Your engine speed decreased because it takes less than one revolution in the input shaft to create a revolution in the output shaft (overdrive). The driveshaft speed is in direct correlation to the rear gear ratio, if you speed up the shaft you speed up the truck. But in overdrive everything ahead turns slower.

 

One thing Coloradogreen was getting st that is true, if you have a truck with 4:30's or lower and everything in OD if you try to run that truck 80 mph or higher your driveshaft and rear bearing will be spinning pretty fast compared to a truck with say 3:55's traveling the same speed.

 

Is number 3 engine miles or revolutions? I drove a Mack that counted revolutions.

 

My guess would be revolutions times a number like a 1000 or something. I can't remember what the Mack I drove had on it. It was revolutions x1000 I think. Anyway being on the tack the only thing it could count is how many times the engine has gone 'round.

After thinking about it, it was times a hundred. But that does not jive with what you have. It would mean yours has an average rpm of about 450 based on hours and tack.