Speedometer issue

This is on a 68 Charger that I bought a year ago and I don't have much history on the car. One day last the speedo jumped up to about 100 and stayed there. A few outings later it moved to 70 and stayed then later it went to 150. It never came back to zero at any time. I knew the speedo was inaccurate from the beginning so this winter I checked the gear in the tranny and it was way wrong. I got the right gear and put it in and when I was done all this the speedo needle was back at zero. On Sunday I took the car out for a run and needle didn't move for a while and then it went to about 10. Then all of a sudden it went to 150 and stayed there. Through all of this the odometer has kept working. The odometer has about 1500 in it and I believe the speedo cable was new at the same time. When I had the cable off the tranny I could roll it very easily between my fingers, there were no sticky spots.
What's going on here? Sorry for the long winded explanation.

Sounds like the speedometer itself is bad. If you have a road with mile markers - and the odometer is close, it's the speedometer. Lots of places still fix them.

https://www.bobsspeedometer.com/1/120/index.asp

The problem is in the speedo head itself, and I wouldn't be shocked if the head just needs to be cleaned and get a drop of light lubrication

The speedometer is new. It shouldn't need cleaning and lubing should it?

Car #4 said:

The speedometer is new. It shouldn't need cleaning and lubing should it?

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No. It's broken.
Mike

Also make sure that the speedo adapter is properly aligned for the number of teeth on the gear.

Car #4 said:

The speedometer is new. It shouldn't need cleaning and lubing should it?

Click to expand...

New repop?
It’s broken , perhaps damaged in shipping. Very delicate