Stx38 problems

Hey guys I haven't posted in a while, but I have had an stx38 for a few years and It worked great until now last fall I used it to mow perfectly then I parked it and now we got some warmer temps so I got it started and everything works except the deck belt is really loose so it will not spin the blades the electric clutch works good , and I even bought a new belt and put it on and that's not the problem then I dropped the deck again and hoisted it up and inspected all of the underside and see that none of the deck lift components have any wear or damage I tried a few of the different holes for mounting the deck to see if that would tighten it up a little but nothing worked I could buy a belt that is even smaller and that would work but I'd rather figure out why it went screwy just sitting. And I bought the manufacture correct sized belt.

There are no idlers for the deck drive it goes directly from the electric clutch to the main deck pulley, I've had the deck off several times in the last three years since I got it and I've been using the same belt and its been tight every time, always has gone off and on with no troubles. even when the engine mounting bolts were all gone(sheared and wobbled out) the belt was still tight enough to work without flaw(besides the motor bouncing side to side).

Here's a link to a service manual https://drive.google.com/file/d/0B_XZLMkMeCkdeHhPWE9Gd0pYdVk/view?usp=sharing
hope it helps

There is a spring on the discharge side, at the back, which hold tension on the idler pulley that the PTO belt runs off of. The PTO belt runs the deck from a double pulley, and the idler spring holds that tension. If you haven't figured it out yet, and need pics just let me know and I'll take some.