67 coupe Mustang
302
C-4 auto transmission
I drove my car last summer and noticed that the speed was off. I have changed the rear tires. Since then I have tore apart the dash and replaced it. I was playing with the speedo cable, gauge(reset the miles) and took the cable out of the tranny to see what gear I had.
I have the dash/speedometer in speed cable hooked up. The cable into the tranny but now the speedometer doesn't work? I take the cable out of the tranny and spin the gear and the speepometer works. I look into the hole where the speedo gear goes and I can see the little gear turning when I turn the tires. I install the gear and nothing?? I thought that I was turning the tires too slow so I put the car on jacks and ran it..Nothing
Does anyone have any ideas?

 

Did you change any of those gears? Be aware that the gears, both in the transmission and on the cable, are made in two different "screw" directions, as well as a number of different teeth on each. The wrong "pitch" gear will fail to mesh with the other.

When you looked into the transmission, did you use a light to see if maybe the teeth on the gear inside were chewed up? If they are, it is easy enough to remove the driveshaft, then the tail housing (transmission must be supported off it's mount), and the gear removed from the shaft. There is a snap ring which keeps it in place, and a steel ball in a pocket in the shaft which drives the gear. If turning the cable makes the speedometer needle move, the trouble is in the two gears somehow. If you determine the need for a new gear or gears, and you have installed different diameter tires than original stock, I can tell you how to determine how many teeth each gear needs to have. Just ask. imp

 

At this point I have not replaced any gears. The speedometer was working up untill I replaced my dash and unplugged the cable from the tranny. The gears don't appear to be chewed up.
Is it possible the gears are not lined up? the little clip is still attached on the speedo gear.

 

Make sure the speedometer cable is inserted properly into the back of the speedometer. Good luck!

 

7 up makes a good point. To eliminate doubt about the gears, disconnect the cable housing from the speedometer head, have someone turn the rear wheels, and see if the cable turns. imp

 

The speedometer work I disconnected the cable from the tranny and taped it onto a cordless drill the speedometer dial moves

 

But you still don't know if the cable turns when you turn the rear wheels (driveshaft). Do that test.

 

All is good. I reseated the cable behind the dash. Reinstalled the cable in the tranny. Seems to be working.
Another question thou...My speedometer is out. Doing some reading and using the calculator. Seems easy enough. Except how do I know what drive gear I have in hte tranny? Lots of Forums just assume # of teeth.

 

I should be able to look in the hole of the tranny. Is the drive gear coloured as well?

 

I would like to get the speedo correct. Can you help me determine what drive gear I have?