Since 1979, Balance Masters has provided dependable Active Balancing Systems for Truck Wheel/Tire assemblies. This technology is now available for driveshafts and has been engineered to fit most heavy-duty trucks, buses, vans and motorhomes. Balance Masters are mounted 1 to 4 inches from either end of the driveshaft. This patented liquid metal (mercury) technology works by centrifugal force. Harmful vibrations are reduced up to 50 percent or more, and this increases the life of the bearings. Balance Masters are made to last and are maintenance free.