Some more info on the 4th gear noise.
I have a 1946 GMC 1.5 ton. Standard 4 speed, no power take off of any kind. U joints are new. Drive shaft is open type. Center propeller bearing is smooth, tight, and rubber propeller bearing cushion new.
I test drove the truck again to listen carefully. The sound always goes away when I depress the clutch pedal. This might be more of a higher RPM that creates this noise. Sometimes Under light load or no / little acceleration I can make the noise go away in 4th gear. This weekend I'll check the clutch throughout bearing in case it's spinning a higher RPM's. I'll also pull the top of the transmission case and look at the 4th gear again for wear. It looked fine the last time was working on my transmission. What should I be looking for with the gear spacers? Is there a tolerance spec?
My dual performance differential has a fair amount of gear lash in the pinion, almost a 1/16" but it runs good with no noise that from the rear of the truck.
Pilot bearing at the crank is new too.
mjl
