Alright so now I know how it works. With the engine off, there is no vacuum applied to the solenoid, so the front axle is engaged. As soon as I turn on the engine it makes vacuum and the solenoid disengages. So to grease front driveshaft start engine. The hunt for my vibration continues. I had the tires balanced. I used my infrared thermometer to check out the rear wheel bearings to see if any are hot, no problem there... Maybe I have a bad tire. I am looking for a rumble that I can feel above 40 kph, sure is frustrating.... I wonder if the rear driveshaft needs balancing. I changed the rear u-joints as one was notchy. Front wheel bearings are new. Anyone got any ideas? <img src="/forums/images/graemlins/confused.gif" alt="" />