Deere X304 belt jumps off 42" deck

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Old 05-14-19, 03:53 PM
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Deere X304 belt jumps off 42" deck

This has been a mystery for me for some time now, and it is getting worse. When I engage the blades in a few seconds there is a clunk and the belt jumps off. I removed the deck and checked everything. The bearings are good, except the idler pulley has some slack. The blades are securely in place. Nothing is loose or bent. Can this little idler slack really cause this? I ordered a new one, just in case. Meanwhile, all ideas are welcome.
 
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Old 05-14-19, 07:07 PM
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Depends on how much slack and how it translates to pulley to belt alignment. I worked on one recently that had slack in the tensioner arm bushing if I remember right. It would jump off occasionally.
 
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Old 05-15-19, 04:03 AM
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When the mechanism to power the blades is in the engage position, the idler pulley should be under constant tension due to it's attached spring unless the belt is too long, The only time the idler pulley has slack is when the mechanism is in the disengage position. There is an adjustment for this. Did you just replace the blade belt?
 
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Old 05-15-19, 05:12 AM
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Thanks for replies.
By idler slack I meant its bearing is somewhat worn. Indeed there is no slack when the belt is in installed. I've had this problem for a long time, occasionally hearing this clunk and belt coming off at startup time. Usually it happened only seldom, and once I got the blades spinning I was able to cut the grass. Now with the new belt it happens every time I engage the blades, the mower is unusable.
 
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Old 05-15-19, 05:47 AM
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I would start by replacing idler pulley bearing, or idler pulley with bearing if that is the way it is sold. Hopefully this fixes the problem. If not and the new belt is not from Deere, I would take it to a Deere dealer and ask them how much to check its length and cross section to the correct Deere belt versus the cost of a Deere belt. If the new belt was made by Deere, I would take it back and have them check it against the belt specifications assuming its the correct part number.
 
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Old 05-15-19, 06:46 AM
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Yes I ordered a new pulley, waiting for it to arrive.
 
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Old 05-15-19, 09:02 AM
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Solved. The belt talk pointed me in the right direction. This is an aftermarket belt and although the length is correct it seems to be stiffer than the original. I started thinking to understand where is the most likely point of failure. I figured this is the right blade pulley, I installed a little blocker there. Two "flat" pulleys on this deck have these blockers, that gave me the idea. The result is amazing - the belt stays on!
Thanks again everyone.
 
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