I have used a bottle jack under a stout 3/4 drive breaker bar and a very large pipe wrench wedged against the floor to hold the yoke. It didn't lift the truck but I could see it un-weight the tires. On big trucks like Jerry worked on sometimes it's just about impossible to get them loose. Fortunately on a truck tractor you can get a good swing with a 3# maul and a big chisel to spread the nut, breaking the rust. Sometimes the fifth wheel is in the way, sigh. Sometimes it takes a torch and a rosebud to heat the nut. But sometimes it's a tanker that had gasoline on last, sigh again. Before you mung up the nut make sure you can get another one. I had to make a castle-nut out of a nylock one time.
