My 74 CJ5 with stock speedometer has suddenly started reading about 20% low and simultaneously, the odometer is reading about 20% low (indicates 0.8 miles when traversing 1.0 actual miles). Previously, the speedometer and odometer were fairly close to correct. As I see it, there are only three possibilities, the gear in the transfer case, the cable, the speedometer/odometer itself. Any suggestions about how I should go about troubleshooting and isolating the defective component? I don't hear any new noises since the problem appeared.