I tested the new unit with a hand vacuum pump.It slid the fork over as it should when I pumped the handle.I did connect it to the unit when I installed it on the axle of the truck.I pumped the handle, but the front wheels did not engage and turn.I felt vacuum on the one hose with the tip of my finger.I don,t know if it is enough.I will try and connect a gauge on the end of the hose and start the truck to see how much is there.My next step is to pull the front cover on the axle and look inside.It will only cost me a new cover gasket,or if I,m careful,just a lil bead of silicone if cover is removed carefully. Hope I don,t find a ruined differential inside the housing....