if 55 is your top speed you probably have a 3.90 gear set.
in 1956 GMC half tonners came with a Dana Spicer 45 rear end.
they had 3.07 gears and in 1958 3.92 gears and posi units that should be able to interchange back through 56.
if you have a 3.90 rear, that is why you shift hard and as the tranny wears out you can get a bangin noise you hear.
You may be able to adjust the shift of your tranny to soften it but several manuals advise against any adjustment because it may accelerate the impending failure of it.(the banging noise you here)
Good luck finding a spicer 45 rear. they are not that common and because parts are hard to find its very hard to pry one away from someone who knows what they have. drums and wheel cylinders are impossible to find.
look around hot rod shops that customise trucks alot as most often the old rear is emoved to install later rears.
I did not know that about the Dextron vs. Ford tranny fluid
Last edited by mike16; 04/17/2012 4:39 AM.
