Finding right speedo gear.
 

My speedometer is bouncing all over the place. I figure this to probably be the gear in the transmission(as that was what it was the last time I had this problem in my 72), but I know it could also be the cable or the speedo itself. Since I put new tires on my truck I need to change the gear anyway I figured I would start there. How do I figure out which gear to get. Is there a formula to use. I know tire size and rear end change it. My tires are 31's but I do not know the rearend at the moment.

Mike

Try this thread.