DrVincennes

I have a dear friend who will be 80 years old in October and he is still messing with cars. I love it and hope I'm doing the same at that age. I was helping him install a new transmission speedo gear in his '65 4 speed. The speedo was off after changing the ring & pinion. He was switching a 22 tooth (green) gear to a 20 tooth (blue). After installing the blue, it would not drive the speedo. Removed it, installed the green, the speedo worked. Installed the blue again, speedo would not work. Removed the speedo cable and saw that the blue gear will not spin in place but does not turn when the car is in gear and running. The green gear measures approximately .875 inch in dia. the blue measures .78 inch. Should these gears be the same diameter? Any other thoughts as to why the blue gear won't drive the speedo?
Thanks

Jeff k

I believe there are two different diameter drive gears available for the transmission output shaft.
You can look up the combinations to determine what you need.

7T1vette

Yes. Depending on the number of teeth on the gear, their respective DRIVE gear (installed on the trans output shaft) is a different diameter. I believe that there are 3 different output shaft gears that could be used, depending on rear axle ratio & tire size. Not all driven gears will work with each drive gear.

Search the internet (Google) for info on speedo gears in the type transmission your friend has. That info may clear up the issue. If the output shaft gear needs to be changed, that can be done by removing the driveshaft and the trans output housing. There are also mechanical "ratio" devices that can be inserted into the speedo cable line which will modify the cable speed as needed. They are not inexpensive; but may be a decent alternative in your friend's case.

DrVincennes

Jeff and 7T1, thanks for the responses. Seems like a lot of work for not much real benefit. May be more practical to break out the GPS.

Jeff k

Best of luck with whatever choice you make!