Craftsman LT1000, 18hp, 42" mower 6 speed transaxle Model 917.273399 After about 20min of mowing the mower sounded a bit louder. A few minutes later vibration, smoke, and a rubber smell comes from the mower area, along with a decrease in engine power. Upon inspection I found a thin rubber coat around the top end of the movable idler pulley that tightens the belt to engage the blades. Also, I discovered that this idler pulley would not spring-return to it's forward position without assistance. I sprayed some WD40 on it and it now returns like normal. A few more tests, the belt continues to vibrate along with a power loss, but without smoke & rubber smell. The engine itself is fine, and this only happens when the blades are engaged. It actually starts to vibrate when the mower clutch is half-way engaged. Upon disengaging the blades, I've noticed the blades take a little longer to stop as if it had more inertia than it should or something. And also this is when the V-belt vibrates the most and once came off the movable idler pulley. The manual says the V-belts aren't adjustable. I replaced the belt, and have the same results. The idler pulleys spin freely and the mandrel pulleys both have an equal tension. Did not try to spin the engine pulley, but I think it's ok. This has never occurred before and I've never done any maintenance for the mower section except replace the blades. They were replaced at the beginning of last summer. Any help is appreciated. Thanks!