Alright. I have a 1987 Rx-7 n/a. When I bought the car it was missing its speedo gear in the transmission and its speedometer cable. Upon replacing the speedometer cable I tested it by spinning the cable with my finger and the speedometer in the instrument cluster works perfectly. I then found a new speedo gear at a u-pull-it from the same year, and model Rx-7 and installed it in my car. My speedometer still does not work at all. Is there something in the transmission that could be goobered up? Has anyone else had this problem? I have never heard of this problem. this is the only thing keeping my Mazda from being a great restoration.

 

If the speedo works with the cable on it,and the cable detached from the trans,then the problem lays within the Speedo gear at the transmission.
Take the 10mm nut off and pull the gear back out.
it should have a plastic worm gear on it that sits on another drive gear in the trans.
If they are not touching you get No sense of speed.
You could always go to Foxed.ca and instead if the Factory service manual,go into the PARTS manual as it will show the parts associated with the cable, the Trans, and what you need to drive the cable.

 

I will give it a look. Thanks.