Driving and Fixing the 1985 GMC C2500

Well I was bored today, so I decided to work on the 1985 GMC C2500. I finally replaced the old power steering V belt that was super thin and worn out, so of course after a repair the reward is a test drive! I still have a mystery squeal!!! Not happy about that at all. Can't think of what it may be. I had the drive shaft out and replaced the only questionable U joint which was the rear one, it showed minimal wear but some of the needle bearings were worn flat so I replaced it. I think it's called a driveshaft carrier bearing? That thing has no play in it and spins free and quiet by hand... Running out of ideas here. I thought maybe it was the poor belt in the front doing it intermittently but I doubt that now especially. Because this truck sat for so long it obviously needed some TLC so I've replaced parts with loose pulley's, worn out or seized brakes, faulty lights etc. Next will be tires and aiming the headlights. Other than that I'm just going to slowly keep plugging away at it when I find time. It'll be great to see it polished and with new cab corners and rocker panels! Some day...