Speedometer or cable problems?

You are darn right about the cigarette smoke and years of contaminates. That crap gets everywhere! Careful cleaning and re-lube can do wonders!
I pulled the entire mess apart and re zeroed the odometer, cleaned everything and lubed the cable w/ weed eater cable lube. It works, but bounces about 5 m.p.h. , but seems to read fairly correct. Well it did before I put 29.5 inch tall tires on it. The speedo gear in the trans. is for a 28" tall tire.