Sounds like the tolerances of the piston to packing may be on the tight side. You could try adding some Cat oil to lubricate the piston and packing. Cat additive is available at most heavy equipment suppliers. Tensioning is done the same as any traction elevator. Is this a new job, or has it always vibrated? Are these pistons single stage or multistage? Any air in the jacks? Does it vibrate in high speed? How quickly is it transioning to level speed? Is level speed high enough? Does it vibrate on inspection? From the getgo, and after inspection for a distance? Does it ever smooth out?
