Speedometers work by measuring rotations of the wheels. The more rotations, the faster your going. But they can't measure in reverse.
You need to lift the collar on the gear stick to engage reverse gear
broken cable? Broken gear at transmission end? Broken gear at speedometer head?
It is possible that the speedometer on a 1997 Plymouth will only work intermittently because the gear is worn out. Sometimes dirt can get up into the area where the speedometer cable is housed and cause excessive wear to the gear.
My speedometer works and the odometer does not because there is a plastic gear in the odometer that is broken.
possibly a broken internal gear in the speedometer head
blown reverse seals
If the speedometer continues to work - probably a broken gear etc. in speedometer head and probably will have to be replaced. If speedometer does not work -- probably a broken speedometer cable
IT DEPENDS, SOME WORK BY GEAR AND CABLE SYSTEMS FROM THE TRANSMISSION. OTHERS CAN BY MAGNETIC OR COMPLETLY ELECTRONIC.
Electronic speedometers/odometers do work in both directions. The old cable driven speedometers/odometers ran backwards in while reverse.
The odds are that the speedometer cable is snapped (it will not look broken so you can not tell without disconnecting it) or the transmission speedometer output gear is broken. Y-THINK-Y
The odometer on a 96 Ford Explorer is tied into the speedometer. If the speedometer is working then there is a gear problem inside of the speedometer causing the odometer to not work.