skeeler Posted September 6, 2015 Report Share Posted September 6, 2015 I have a '77 Datsun 620 pickup that drove perfectly fine after I first bought her but she's starting to develop a few 'quirks'. The odometer has always run waaay too fast (the numbers are actually closer to how many MINUTES it's been driving) but the speedo was accurate until just a few days ago. It runs 15-20 mph too fast and on highways tends to get stuck and spastic at around 80 (or 70?) Maybe just adjust cable union nut/replace cable but would that just fix speedo? How to deal with odometer readings? I have the original rims and hubs but the tires are P205/75R14's. Not sure if that is the totally wrong size I know 205/60R14 is acceptable. Could that account for such a huge issue with the readings? Appreciate any and all help. Quote Link to comment
thisismatt Posted September 6, 2015 Report Share Posted September 6, 2015 Bigger diameter wheels would make the speedo slow, as the larger diameter means bigger circumference and therefore farther traveled per revolution, and the speedo is reading revolutions at the transmission. Quote Link to comment
datzenmike Posted September 6, 2015 Report Share Posted September 6, 2015 Jumping spastic speedometer needle is always the inner cable rubbing and gripping the outer sheath. It's really a small and very long tightly wound spring and it will keep turning and storing energy. When it breaks loose, the speedometer gauge will jump. Inspect the speedometer cable for kinks and damage on the under side of the truck. If damaged no sense trying to fix it. They used to be available for about $20. Too long is ok if you have to use another model. Otherwise unscrew the transmission end and slip the inner cable out. It is very flexible and floppy so be prepared. Likely it is dry and needs lube. If rusty suspect a hole in the outer sheath and replace. Use a dry graphite or liquid molybdenum dioxide grease. Put back in and twist/spin the cable with fingers to be sure the other end moves the gauge end. Be sure to slip the ferule into the slot on the transmission pinion sleeve and hand tighten. The odometer is gear driven (unlike the speed gauge part) and cannot be driven faster than the vehicle speed even though it may seem that way. Quote Link to comment
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