One thing to remember for those that have the 39 and 809 series 5 tons is the sprag transfer, to make the hubs work, the transfer needs the air cutoff mwo, this cuts the air to the poppet valves, putting the sprag into neutral, without doing this the transfer WILL think the rears are spinning because the front tires are not driving the OVER RUNNING clutch (sprag) in the transfer, and WILL ENGAGE the sprag which will drive the front 3rd member.