Speedometer issues (Shelby Lancer)

I'm having a hell of a time trying to get my speedometer working in my Shelby Lancer after it had sat for a long time. Ever since getting the car running again last year, the speedometer (mechanical cable driven) jumps around all over the place, or it's seemingly dead with the needle stationary below 0, or when it does work, it reads about 25 MPH too fast. I also hear a faint jingle sound from the cluster, like a tiny bell ringing randomly when I drive it which seems to coincide with the needle jumping all over the place. I have another H-body instrument cluster (original from the car) and it does the same thing including the ringing sound.

I know my speed sensor and drive gear is OK. The cables I'm not too sure about. It uses an extension cable which I tried removing and no difference.

I'm not sure if this means the speedometer is broken, but maybe the best fix is to get an electronic cluster from an '89 H-body car and get rid of the cable entirely?

You sure it's not the speed sensor?

https://www.youtube.com/watch?v=F83NtIg4x7I

I haven't hooked up my OTC 4000 to it yet, but I'm pretty sure it's a mechanical issue with either the speedometer itself or the cable. No codes as far as the speed distance sensor. I have a hunch that the cable is binding and not spinning smoothly, therefore 'impacting' the speedo, causing the jumping. Either that or the tiny square shaft on the end of the cable is stripped out within the speed sensor.

Next I think I'll remove the cables and flush them with WD-40 or maybe a graphite lube. I just hope the speedo isn't actually broken. The jangling/ringing sound seems to be coming right from it.

Lubricate the cable. I've had that problem before, sprayed some Liquid Wrench penetrating oil inside the cable and it git better.

Sounds to me like your guage is kapoot.
Cable driven bouncing around or not working sounds exactly like a bad guage. I had to replace the one in my L body, did the same thing as what you describe including the bell sound.

My SL did that a bit when I bought it. Got a cable from the j-yard and solved that issue. But the next time it runs will be with an 88+ electric speedo.