Speedometer Flutter

Sorry to hi-jack this thread, but I don't think we need another speedo question on the forum; lol
I'm having the same issue. Here's my background: New cable, lubed before installation.
Speedo bench tested with drill before installation, no jumping and flutter.
The new cable was a 62" and that was replacing a 63" that came out.
I'm thinking I may have too sharp a bend in the cable. It comes through the firewall loops down to the tranny. The "loop" does not go past the edge of the master cylinder.
any thoughts?

1970 Plymouth Valiant. 318. I believe it's a 904. Not sure, though. I have not taken a close look, but the PO said it used to be behind a 360.
thanks