speedo

speedo needle jumps at 55-60 mph....sometimes......under wot it cant keep up.....cable or speedo needing repair????,,,,tia

Lubing the cable may help. You can pull out the inner wire, spray some WD-40 down the housing followed by compressed air, dribble in some engine oil, and then reinstall the inner cable. If that doesn't help your gauge is getting crunchy. You can crack it open by prying off the crimp ring, but I'm not sure how to advice you to fix it one you get it open.

Yes do as Nessism suggested for starters. Before You attach the cable to instrument hold the top of the instrument firm at the top and try to wiggle the threaded cable end of gauge. If You feel any play the drive, with spinning magnet, is wandering inside of drag cup. This causes spikes in what you are seeing. If You have a discoloration in face of gauge where needle is mounted then the damper fluid probably too low to be of any use for keeping the needle under control, this too will cause a slight spiking issue. I assume yours is the 160mph version? Let me know I can walk you thru the process if your brave.

I lubed the cable but have not tried it out yet....there is no discoloration on the glass or damage any where,,,,will advise when I know more

When the cable is starting to fail it will lose some of it's strands. Take it out and twist it. If it twists a lot that could be the issue. It will act like a spring loading and unloading while turning. That will cause the needle to fluctuate sometimes WILDLY.
Steve