OK folks. New on here, not new to fighting lawn tractors. I lost a belt as I was finishing the backyard yesterday. I ran over a rubber mat and the already worn belt broke.

But I had a spare and went to putting it on. Used my operators manual, diagram on the mower and diagram on the belt package.

Put it on and didn't finish the front yard before the new one burned up and broke off..

The old belt snapped but was still on so I put the new one on exactly like the old. All the pulleys turn freely. There were no sticks in the pulleys and the belt cover was off.

If the deck was set at 2 or below the drive would engage and disengage as it should. If I raised it higher the drive would start running without engaging it.

I adjusted the belt tensioner to no slack but not tight as the manual says.It seemed to help some as the deck could be raised and the drive would stay off. I'd cut some, stop and inspect then cut some more. All the pulleys are turning. Its always garage kept and never washed(so the bearings on the deck should have never been wet).

How tight is the tensioner spring supposed to be? What about the brakes on the blade pulleys? The new belt went on just like the old. It got a groove burned in it so I ran it trying to finish before it rained and blew the rest of the belt off(didn't get finished either).

Hi,
Not clear what the belt is driving, motion or deck. If motion then I suspect the rear plate over the transaxle sheave. If deck well there too many posibilities but do not rule out spindles though they may have not knowingly exposed to water.
Peace,
Clarke
PS My sig is not showing up , so OPE by Crigby (http://opebycrigby.tripod.com/)

The arm on the front of the deck has a adjusting nut on it ,turn it in some a little at a time until the belt doesn't catch,

It's a 125 42" mower. 1 belt runs from the PTO around 4 pulleys.. Haven't looked at it again. It seems the belt was binding on something.. Guess the easiest thing is to try again with another belt. When I hit the mat the belt snapped quicly so I don't think there was much strain on the deck. What about the adjuster? How tight should it be. The belt looked like it was flopping around.