How to Troubleshoot & Replace Whirlpool AP5983729 / 661570V Whirlpool Drive Belt

Parts 

Found the offending part (thermal cutoff) and then down the rabbit-hole of why it tripped. Turns out the motor was failing and could not spin the blower wheel fast enough to move the air out of the dryer resulting in an overheat condition, thus tripping the cutoff. 

Replaced drum belt, wheels, and tensioner 

New belt 

Repalced the belt 

A couple YouTube videos were very helpful. It's remarkably straightforward. 

Thanks to ApplianePartsPros.com's great videos I was able to diagnose the problem, order the part that arrived quickly and repair my dryer. 

Purchased new belt and tension idler pulley. 

Replaced idler pulley, and while I had it apart decided to replace drum rollers and belt on this 12yr old machine 

I replaced the idler pulley assembly and belt. The belt was actually fine, but while I had the dryer disassembled I changed the belt as well. The repair took me a while, because there are a lot of screws to remove. I think this repair would probably take about 1-2 hours with more experience.