I have a 1948 3100 original truck. The speedometer recently started making a screeching noise so I unhooked the speedo cable and used white lithium grease to lube the cable. When I hooked it back up, the speedometer started moving up to about 10-15 mph then dropped back down and never moved again. The odometer is working fine so I'm assuming its not a cable problem but a speedometer gear problem? Do I need to replace the whole unit or can I replace the gears? or is there another fix to try? Thanks so much!