Rally Dash Question

I put a Rally dash in my 70 Dart and the odometer quit working. The speedometer stills works. Any idea what broke? I think they both run off the gear and cable from the transmission. Thanks for any info.

Internal odo failure... the speedo and the odo work both separatelly but of course reaction on the same main worm.

The main worn is attached to the driveshaft which makes work the axle to move the magnet assembly.

Then outer gears are geared to this driveshaft worm to make the speedo to spin. Usually two other worms to reach the odo gear.

Thank You I guess I will have to remove inst. cluster and check it out.