[Pizzaholic]

I know this thread is several years old, but I found it searching for info on the SM420 4 speed manual in my '62 C10, so in case others also find it in the future...I think that the original post said that the previous owner had the return spring pulling the clutch fork toward the back of the truck. I think the return spring needs to be mounted such that it pulls the clutch fork toward the front of the truck so that it "returns" the fork to the original position thereby re-engaging the clutch, hence the name "return spring." That may have been the issue all along.