Some one can correct me if I'm wrong. I believe you select the position then when you feel the rpm is right just let off the gas briefly(maybe tap clutch)then hit gas pedal again. The two speed should shift at point of no load when you let off gas. My experience with the 2 speed rears was with electric shift models. The vacuum shifts may reqire a little more time. (The air shifts between Direct and overdrive on modern transmissions is quick.) You will immediately know if you've missed the shift as a 2 speed between gears makes a heck of a racket then you have to play with gas pedal and clutch to get things lined back up. Many people used to just wait until they got into top gear and then shift to the high side. It's all developing an ear for the rpm and the timing of the shift. Have fun.The down shifts are a little tricky as you have to bring the engine rpm up to sycrhonize the drive shaft speed to the lower rear gear.
