http://www.1aauto.com/1A/Weatherstrip/Chevy/Pickup-CK-Series/1AWSX00507
1A Auto shows you how to replace your window channel and sweep weatherstrip. This is a pretty easy project if you know the steps beforehand. Plan on about an hour per door. This process is generally the same on all 1973-87 Chevrolet and GMC C/K Series Pickup trucks, K5 Blazer and JImmy, and Suburban. The specific parts may differ for the 73-81 vehicles but the process is generally the same.