Cub Cadet riding mower belt issues

[LFD2037]

idler pulleys are shot

They weren't in my case. Once we got the correct length belt, issues went away & my dad hasn't had an issue since this one (4 years ago).

[dfkoon]

or the idler pully spring is broken.

[Walker]

Never worked on a cub, but craftsmen and huskies have keepers that fit close to the pulleys to keep belts on when not engages. In fact you have to loosen or even take them off to replace beast. They are a pain but serve their purpose.

[60 Deluxe]

There should be a spring loaded tensioner pulley to keep the belt tight. It will have a 3/8" hole in the bracket to use a breaker bar to pull it back while you put the belt on. If that is there and working correctly, there is no way that you can put a belt 3 1/2" too short on. It is a struggle to get the correct belt on having to fight the spring with one arm and put the belt on with the other. I usually pull the tensioner back and wire it out of the way while I route the belt. My guess is you only think that you have the belt routed correctly. I was working on mine about a month ago and realized that I had put the belt on where it was running with the back of the belt riding on the drive pulley. It worked good for a couple of years that way. While you are messing with it, check the bearings. I thought that they were sealed and realized that they are conical bearings and need to be greased every now and then. I removed the spindles and cleaned all the old grease out and repacked the bearings. Found the zerk fittings for greasing the bearing while I was doing that. Twenty plus years with no fresh grease. Oops.

[Abctx]

For those that don’t know, Tractor Supply has a “belt aisle”. They have an entire rack of belts sorted by length. They also have a gauge there so you can measure your old belt. FWIW...

[Tony Pic]

I have a CC LT1040 and had the same issue. I replaced the idler pulley and spring. It called for a 122" belt and it kept falling off. I went to a smaller belt. 100" and have had no issues since. The idler pulley was a wee bit larger(amazon purchase)but I needed it and it fit.
It cuts like a brush hog now.
I have been thinking about an upgrade also in a Zeroturn. But right now, the CC does the job.

[Abcdj]

Mine kept coming off when I engaged the blades. Tried lots of fixes. The guy at a small engine place told me to raise the deck as high as I could before I engaged the blades. Then engage the blades and lower the deck. I thought he was nuts. He said something about angles and geometry. Believe it or not it has worked everytime!
Hope it is as simple is that for you.
Also mine is a Bobcat zero turn.

[PeePaw on Fork]

Used to have the same problem
All of the deck pulleys wear out
They should have a v shape to hold the belt
Drive pulley is probably worn down also

[PeePaw on Fork]

Had to replace all the pulleys on my cub cadet several times...they wear enough that they actually separated. When worn down the belt won't tighten up.