Bouncing Speedo Cable

[68 ReNay]

my speedo's been bouncing once it hits 65mph for some time. i replaced the cable (cable and housing unit). now it bounces from 1-50mph then stops til 65 and starts bouncing again. so i graphite lubed the cable-no change, pulled out speedometer and put a couple drops of oil in the back of it-no change, i added more graphite oil to the cable-no change - but just today i began hearing the scraping sound (only noticed it at around 45mph). both 'holes' for the cable ends don't appear worn.

i'm at a loss. is it just the speedo itself that needs to be replaced? the speedo gear? it's so annoying to put on a new part and have the problem be worse!

it's a 68 1/2 ton. 350 small block with TH350.

any help is extremely appreciated!!!