I have seen this problem too many times.
There is a reverse speedo gear for automatics and a normal rotation gear for the manual transmissions. There is also a reverse speedo gear on the transmission and a normal speedo gear on the transmission. You have to have them matched correctly.
On our cars, we put the reverse rotation speedo gear on the output shaft of the toploader 4 speed and put an automatic speedo gear on the speed cable. That way, the reverse speedo works with NO reverser!
You also have to be careful because there are DIFFERENT tooth counts on the speedo gears on the tranny and on the cable. It can be a nightmare if you don't have it set up correctly.
We ate many a gear before we figured out what was going on. You have to match them.
David
