General Motors, in their repair manual, calls their 3 speed trans the "The GM 3 speed transmission". And the 4 speed is lovingly referred to as "the GM 4 speed transmission". The 3 speed is synchronised in 2nd and 3rd gears. The 4 speed is not synchronised. I have an NOS 4 speed which I could not upshift without double clutching. I've driven semis for many years and know the technique, but I could never get it to shift clutchless, it was so tight.
3 and 4 speeds can be interchanged with each other as the 4 speed was an optional trans. The u-joint is different however. The front half remains the same but the rear half of the u-joint for the 4 speed is of a coarser spline. (10 spline I seem to recall)
I have one of each trans if anyone needs measurements.
Last edited by k10; 04/25/2011 7:21 PM.
