First time rebuild problems-trouble upshifting

TheCraigMachine said

Im going to build another valve body. I have a couple of extras lying around.
Does anybody know what the shuttle valve does? The reason I ask is because one of my extra valve bodies doesnt have a spring behind (or in front of) the shuttle valve. What purpose does it serve?

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That sounds like a good idea. I have read everything I can find and can't seem to find a description of what the shuttle valve actually does in a torqueflite. If I'm not mistaken I've read that blocking it firms up the shifts but I have never blocked one and have had torqueflite's that shift as firm as you'd ever want one to shift. I know someone that may be able to shed more light on the shuttle valve. I'll PM him and see if can help