72 Cruise cable seems to be "walking around" so I loose speedo

[anotherriviera]

I converted my 72 to a cruise control car a week ago. I still am missing the switch but the rest is all there and plugged in. As I drive it though I loose the speedo, the cable seems to be moving to either one side or the other. Meaning the cable moves too far inside the cruise servo or too far into the speedo assembly, and thus I lose the speedo till i unscrew the cruise servo and pull/push the cable back. This is the 2nd Riviera I had do this to me. Any ideas? Is there any chance that the speedo head has a shorter/longer input shaft for a cruise car? All cables and servo move freely. It seems to only be affected by the top cable, the servo to speedo one.

Thanks

Bill