All of a sudden my speedometer is showing speeds that are about 20 to 25 mph faster than I am actually going...nothing has changed. What could cause this and what might the fix be?
If you have an original speedo, the cable just turns a metal piece that is around a magentic pick up (or vice versa, I don't recall)- this could be hanging up between the two which would kick the needle up to a higher speed. Not sure of a fix for that, possible lube, or might be a repacement. If its jumping around, then it's likely the cable needs to be cleaned and lubed.
Likely needs lubrication. My Fairlane does similar in cold weather, original lube turns to glue. It's fine in warm weather.
