We have a 1989 GMC pick. The water pump went out and we replaced it. Apparently the new one had a bad shaft that was crooked. It threw the serpentine belt off while we were driving. We again replaced the water pump and got a good one this time. We also replaced the tensioner. It still throws the belt off. What could be making this happen.
Oct 12, 2007 at 8:07 AM