Cab leaning, need help

[Shak]

I've been admiring this site and the information it provides for a while now. I just began the tear down on my 51 AD, and after removing the bed, immediately noticed the cab was leaning considerably to the drivers side. All the mounts are tight and appear fine. The frame is straight and the truck hasn't been in an accident, as best as I can tell. Can anyone tell me why it might be leaning, and what I need to do to correct it. Also, when you are looking at the truck from the back, how high off the frame should the bottom of the cab be?

[OrrieG]

assuming you put a level across the frame behind the cab and leveled it, then checked the cab it really can only be a couple of things. 1. bed mount points on the cab are rusted and weakened causing sag. 2. Frame mounts are rusted or have been tweaked. 3. Cab mounts themselves have been compromised on one side, even though they are tight. At one point someone may have replaced one with wrong size. 4. Truck has been hit from the side.

If the frame is not level side to side with equal size tires and wheels in place, a spring is weak or spring mount/frame has been compromised. Start with getting the frame level, then work on the cab. Pictures would help.