I don't know about all of them, but several zx's I looked at also had broken speedo's, including the one I bought. It also could be the cable needs lubrication, but my experience has been the speedo.
You can replace it with a 130mph, or another 85 mph unit fairly easily. The gage cluster comes out if you drop the steering column and have small hands to unplug everything. The cluster comes apart easy by removing a few screws. If you have the check computer, it is a bit tricky to get that back in just right, but fairly easy.
Joe at All Z East should be able to help you in getting the speedo, just let him know if you have cruise control or not. They seem to have the best prices and supply that I have found. Send him an email at [email protected]
. You can call his 800#. Look for it in other posts here at zcar.com. I don't have it handy.