I believe most are replacing the old chain drives with modern cable drives that have Tee adapters welded or braised onto the ends.
I recently bought a digital bicycle speedometer that uses a battery like a hearing aid. I hot-glued the magnet pick up to the wheel gear and ran the two small wires up the original speedometer sheath to the dash of my 13 Buick.
Now I have an silent & accurate speedometer that also gives me the time, distance traveled, etc.... It was on sale for under $15.
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Mark Shaw
BCA PWD Director
HCCA Member (Skagit & Portland)
1913 Model 31 Touring
1915 Model C-25 "Speedster"
1924 Model 45 "Roadster Truck"
1929 Model 29-27 Sedan (Now my son's car)
1931 Model 57 Sedan
1938 Model 48 Sedan