I've always been told that graphite is absolutely NOT supposed to be used on speedo cables. White lithium spray-on grease is preferred.
Checking on a number of forums, it seems that it's about 50/50 between white lithium and graphite based lubes. Nowhere did I see NOT to use graphite. The 47-51 Service manual calls for AC speedometer cable lubricant, whatever that is.
All of the stuff I saw said not to gob it on, and the service manual says lube only the lower portion of the cable. One guy mentioned having a pile of grease under his dash as it got pumped up the cable.
