Speedometer doesn't work

[challenger]

My 1970 300 speedometer stopped working years ago. Being driven about 50 miles a year it wasn't a big concern. Now I plan on driving it much more so I replaced the cable which was broken at the cluster connector. The cable wouldn't clip into the speedometer so I thought replacing it had to be the fix. Well now that the instrument cluster is back in I find it still doesn't budge off zero. Is there a common problem that happens to these?
Thanks

 

[Davea Lux]

My 1970 300 speedometer stopped working years ago. Being driven about 50 miles a year it wasn't a big concern. Now I plan on driving it much more so I replaced the cable which was broken at the cluster connector. The cable wouldn't clip into the speedometer so I thought replacing it had to be the fix. Well now that the instrument cluster is back in I find it still doesn't budge off zero. Is there a common problem that happens to these?
Thanks

A lot of times, the reason the cable breaks at the cluster is because something in the speedo head is bound up or broken, as the cable is the weak link, it will be twisted off.
I would try unhooking the cable from the speedo to see if it has failed. If it is intact, try turning the square end of the cable with your fingers. It should move a short distance and then lock up, this means that the cable is seated in the drive gear for the transmission and the cable itself is intact. Try turning the input of the speedo by hand, it should turn freely. Jack up one rear wheel of the car and have a helper turn the wheel, the cable should turn at the speedo head as the wheel is turned. You will need to do this operation in neutral, so be sure the vehicle is properly blocked so it can not roll away. If the cable doesn't not turn as the wheel is moved, either the cable is twisted off someplace or the drive gear on the transmission has failed. If the cable turns as the wheel is turned re-install the cable to the speedo being careful to insure that the square cable end is inserted into the square fitting on the back of the speedo.
Test drive the car, if the speedo still is non-functional, you have a bad speedo head.

Dave

 

[challenger]

Thanks Dave,
One item I should have perhaps mentioned is that the replacement cable, which is brand new, is a fair bit longer than the original. I don't know what impact this may have if any. It has a much bigger loop inside the engine compartment.
Any idea if the cable spins clockwise or counter clockwise? I'm curious if just taking the transmission end off and spinning the cable by hand would eliminate the cable as being the problem. Obviously if the speedo moves when turning the cable by hand the speedo is, is likely is, good but I don't know if this would totally eliminate the cable being at fault considering it is much longer?

 

[Davea Lux]

Thanks Dave,
One item I should have perhaps mentioned is that the replacement cable, which is brand new, is a fair bit longer than the original. I don't know what impact this may have if any. It has a much bigger loop inside the engine compartment.
Any idea if the cable spins clockwise or counter clockwise? I'm curious if just taking the transmission end off and spinning the cable by hand would eliminate the cable as being the problem. Obviously if the speedo moves when turning the cable by hand the speedo is, is likely is, good but I don't know if this would totally eliminate the cable being at fault considering it is much longer?

As long as the cable and housing will attach the extra length should not hurt anything, although if you had it fabricated, it should have been made the same length.
You can detach the cable from the transmission and spin the cable with an electric drill, just be careful not to let it kink. Best to hold the drill steady and have a helper check the speedo function. Do not remember which way it turns, won't hurt anything if you turn it backwards as the car had to back up which turned the cable backwards. Try it the other way if the first one doesn't work. If the cable is properly engaged with the speedo head, it should at least register a tenth of a mile as you turn it in the right direction. If it doesn't, the cable might not be seated in the speedo properly. If it is properly seated, your speedo is dead.

Dave

 

[cbarge]

You can use a cordless drill in REVERSE or counter clock wise to test the speedo.

 

[challenger]

Thanks folks!
I will check things out today after mowing the grass .
I'm curious if there is a common piece or part, within the speedometer, that's to blame whenever they break? I just put the whole cluster back into the car after fixing the fuel gauge and the process is still fresh in my mind (more like burned/etched like a life event we wish we didn't get ourselves into ) so taking it out again would be less painful now as opposed to months or years from now.
Thanks again!