My tale of speedometer woe...
When I got the truck the speedometer was off, read 5-10 off consistently. First things first, I calculated what drive/driven gear I'd need for my rearend/tire combo. Pulled the speedometer cable and tail shaft housing from the trans. The driven gear in the tail shaft was eaten up pretty bad. "Great!" I thought, this will fix it. Nope! Speedo worked well up till about 30mph then read 5-10 low.
Next up I thought maybe the cable was binding? Lubed it up with graphite and tried different ways of routing it to no avail. "Well, maybe the cable is just old and worn out?" I thought. Picked up a new cable, but still I was without an accurate reading.
Finally I figured maybe the speedo head must be bad. The one in the truck was original. When I removed it and spun it by hand it made a faint metallic clinking noise in one spot, and the whole apparatus had play in it. "This must be it!" I thought. Ordered a speedo in good working order (per the seller) and when it arrived I cleaned it up and looked it over. It was clean, tight, and worked well with the old drill test. Installed and still no accuracy!
After all of that the truck would read accurate up to about 25-30 and then I would get bouncy speedometer and it would read low (going 45 speedo would say 35-40) I rerouted the cable again tonight and now the speedo is reading high!
I'm certain at this point this surely must be a speedometer cable issue? I don't have any sharp bends in the cable and its held loosely in place by zip ties. What am I missing????? Should it be held in place more securely? Is there a cable routing trick I don't know? Were bouncy speedos the norm in the 60's?? Do I need to pony up for a speedo head rebuild? Any help, pictures, or advice would be greatly appreciated because I'm at a loss of what to do
I gave that a try and the cable was spinning smooth. Guess I’ll look for another speedo. 