Speedometer broke. For the second time.

1965 Plymouth valiant gauge cluster. Cheap aftermarket replacement cable.

Speedometer works fine for a couple of thousand miles. Then it starts bouncing all over the place and stops wherever it wants. Usually around 30 mph. You reach up under the dash, unscrew the cable from the speedometer and it falls back down to zero. You screw it back in and take it for a drive and it works for a little bit and then does it all over again.

I talked to a couple of speedometer shops on the phone. The price they were quoting to fix the speedometer was astronomical. Upwards of $450.

But here’s where the confusion starts. The first shop told me it was because my cheap Chinese cable was too long and putting pressure on the back of the speedometer. The second shop, which is also been in business for 60 years, told me that this is not possible. And then I just happen to have two shitty speedometers that broke just after installation.

Can anybody shed some light on the subject? I know I need to find another speedometer head, or get one of these repaired. But cut the cable because in this problem? What is the solution.

Thank you in advance. Eric and Jason.