That gravity method will only work when the master cyl. is up on the firewall. These older trucks have the master cyl. on the frame & the fluid will not flow up to the wheel cyls.
Its raining too hard for me to go look at whether the master cylinder is below my wheel cylinders or not on the naked frame beside my garage, but I have gotten frustrated in getting all the air out and just left the stupid thing for a day or two, and sure enough the air escaped somehow. I am guessing it found its way to the master cylinder. I don't know if it can travel all the way from the wheel cylinders or not.
