A couple of notes on speedometer repairs.

Failure mode 1: Pushing in trip odo while moving results in 
breaking/splitting of odo drive gear.  Apparently heat may do this too.

Fix - Glue pieces together, wrap with string and glue, epoxy, super 
glue to shaft.  Hard to find unbroken gears at wreckers.  Sometines 
split gears are still in the housing and are gluable.  Can get 
discount on broken instrument cluster due to lack of gear on shaft!
I managed to buy (2) for $50 and ended up with 2 complete working 
cluster after various repairs.

Failure mode 2: Shaft itself is secured in place in housing with 
friction only.  Shaft slides in housing thus becoming disengaged with 
drive gear.

Fix - Glue something to housing to prevent shaft from moving, 
plastic, wood, etc.

- Jeff