Thank you, Travis.
I did go to Commercial Speedometer today.
First, I partially disassembled the instrument panel to get the speedometer out. I tested the operation of the speedo with a cable and a drill.
Just an FYI… the cable turns CCW to operate the speedometer.
The guys at the shop thought my speedometer can be fixed but I’d need to supply a few parts since they don’t stock them for a 54 year old Dodge.
I came back home and tore down another cluster.
The one in Jigsaw is original to the red car so all the gauges are equally “seasoned”.
Check out the face of this one:
Just like the others, this one won’t return to zero but it does work without binding.
With my “good” speedo, The counter man at CS noticed play in this part:
Note where the white pointer is aimed. That silver colored drum can move fore and aft slightly but should not wobble side to side. This is one reason for a bouncy needle. Mine was wobbly so I have to bring in something in better condition. Looking at some other units here, it seems like Ma Mopar used a common speedometer design in the golden era… here is a mid 70s A body:
Looks similar aside from the face plate. Here is a ‘68 Satellite (thank you Dwayne)
Sometimes you learn how stuff works by taking it apart. I saw this:
To the left you see a silver colored tang. It appears that it is meant to be a “stop” for a peg on the drum seen here:
That peg makes contact with the drum to limit the range of the needle.
The drum doesn’t spin with the cable. It rotates as the speedometer needle moves.
The shop is closed tomorrow so I’ll return there Monday with a spare Charger speedometer and one each from the Dart and Satellite. If they are the same, I’d prefer to keep the other Charger speedo intact for a spare.