I have a 41 GMC. Stock 4 speed. Got it all back together and took it for a drive. The speedo doesn't work and the odometer runs backwards........ What did I do wrong???

Did the speedometer ever work properly before?

Speedometer drive gear in backwards in the tranny taillshaft?

Speedo cable was not hooked up when I got truck. I have had the trans out and the tail shaft off. Didn't know I could put it in backward.

Are you driving in reverse, you showoff? 😉

Honestly most of the time I've seen this is because somebody at some time installed the wrong speedometer drive gear. Some point one way and others point the opposite way.

If you disconnect the speedometer cable at the transmission and look at the end of the gear that drives the cable, it should be turning clockwise as the wheels turn in a forward direction. Jack up one rear wheel and either have someone spin the wheel by hand or let the engine idle in 1st. gear. If the gear is turning the proper direction, try the same check by disconnecting the speedometer cable inside the cab. There might be a speed change gearbox somewhere between the transmission and the dash that is assembled incorrectly.
Jerry

Is there any indication that the speedometer has been rebuilt? The last time I had one open, it looked like that it is possible to reassemble it incorrectly. I do not know if that will make it go backwards.

Is the speedo cable attached to the drivers side?
If I remember correctly the driven gear can be installed to come out either side of the transmission. If the cable is attached to the passenger side it will turn the speedo backwards.

Thanks, Ill try this first. I is on the pass. side