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Mower had been working fine this season, but when I was sharpening the blades, I noticed the secondary belt (one that goes around blade spindles) was worn, so I decided to replace it. Found a belt on Amazon that was touted as a replacement for the exact part number, and I checked the belt after receiving it to verify that it was proper length (width is slightly greater, but only because of the old one's age) - seems to be the exact same thing.

Here's my problem, though: When I try to start the blades with the new belt, the belt comes off the tensioner pulley. I have followed the instructions to the best of my knowledge- I have checked the routing against the book and a picture of the mower with the old belt on it. I have tried this three times, and this problem happens at low and high throttle. The belt seems tight when the deck is on the floor, so it does not appear to be loose or anything.

Tractor is x540 with a 54c mower on it.
 

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Welcome.

I think most everyone on here will agree that OEM JD belts are the only way to go. You may find that it will correct the problem. If the old one didn't jump off the new one shouldn't if it is correct.
 

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Discussion Starter #3
Welcome.

I think most everyone on here will agree that OEM JD belts are the only way to go. You may find that it will correct the problem. If the old one didn't jump off the new one shouldn't if it is correct.
I appreciate the advice. However, I am not sure what would be wrong with the new belt, as the dimensions are the same. Is there any adjustment I can make that will allow this belt to work?

Also, this is my first time replacing this belt, so I may have overlooked something, but I have checked the big things like proper routing.

This is what I'm working with (not my pic, but same type): JD_Mower_Deck_1-002.jpg
 

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If it is installed correctly, check the alignment of the spindle sheaves, make sure the spindle bearings are tight, check the alignment of the idler pulleys and their bearings.

Do the specs on your replacement belt show the same angle and depth? Also JD OEM belts are constructed differently than a standard V-belt.

There are quite a few guys on here that are much more familiar with these than I am and I'm sure will come in on this at some point. I think there is a section on the JD Parts website on belts. If the Alabama-Missouri game doesn't get more interesting, I'll see if I can find it.
 

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Discussion Starter #5
Just checked the bearings and they all seem pretty tight. Regarding alignment, I don't see anything very unusual, but I don't know exactly what to look for. They all seem to be in the same plane, except the flat spring-loaded idler is slightly higher, but not significantly. I think it is supposed to be that way though because the belt has to be slid underneath it to put it on and the instructions don't say anything about unbolting pulleys. I don't think I have changed any of that stuff though anyway, and the mower was working fine with the old belt- I just decided to replace it now so that it doesn't break on the job next season.

Visually, the new belt looks to be the same shape. However, it is white compared to the old one being black. Probably just different dyes for the branding, but who knows. This is the replacement one - the part number it claims to replace is the same one in my manual.

http://www.amazon.com/Replacement-John-Deere-M154960-Specifications/dp/B004F27Y4O
 

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Discussion Starter #7
Update: just put the old belt back on and the mower worked fine. The belt sits a little bit deeper on the pulleys due to less width, but again, I think this is due to age. Do you think I have a good chance of solving the problem just by buying a genuine part, or does something need adjusted also?
 

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Don has given you great advice, OEM is the way to go.
 

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...one last thing to try before you get your OEM belt.... Make sure that any and all tensioning springs are hooked where they are supposed to be hooked at both ends. Sometimes we "forget".:laugh: Where is the belt jumping off, can you tell? Check the vertical AND side play in the pto/deck drive bearing/pulley. I'll bet that is where it flies off when the clutch kicks in, the variance in the belt profile is probably what's causing it though.
 

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As others have said buy OEM, Before installing the OEM belt compare the two and see what you find.

Doug
 

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Discussion Starter #11
Ok, so I have held the belts up and stretched them out, and the old and new one appear to be the same length. The package for the new one says 5/8 x 121.3 inches, and has the correct JD part number on it (see my link above for the belt I bought - PIX belt from AMC on Amazon). However, the page where the belt was advertised says the dimension is 5/8 x 120.3 in. So maybe the new one is an inch too long? Maybe it seems tight when I install it, but is not really as tight as it should be?

I'll be calling my John Deere dealer for an OEM belt on Monday. I'll let you guys know how I ultimately resolve this.
 

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I have tried this three times, and this problem happens at low and high throttle.
QUOTE]
Sounds like the tensioner system is not responding fast enough or at all.
Remember the new belt is going to be a lot stiffer than the old one.
Just guessing, but to me it would be a tensioner problem if excessive belt
slack is building up right ahead of the tensioner pulley, if that's where
it's jumping out each time.
 
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