Lubricating speedometer cables
Though I know people who have used sewing machine oil and other light oils and greases to lubricate speedometer cables without an apparent problem, I generally prefer to use dedicated cable lubricant. There are numerous different brands with one example being Royal Enfield’s cable lubricant product #Z90943 (www.royalenfieldusa.com).
There are several different tools available that allow you to force lubricant into a cable casing with the cable still inside of it but whenever possible it is definitely preferable to remove the cable from its casing so that all of the old lubricant and foreign matter on the cable and in the casing can be cleaned out. If you don’t clean them out, the bits of metallic particles and other debris will act as an abrasive as the cable spins even after you inject new lube. It is important not to put too much lubricant into the cable housing, particularly toward the speedometer end, because it may have a tendency to migrate into the speedometer head and cause damage.