Belt on finish mower slipping?

[Arc weld]

Can a belt loose it's tension/stretch just because it's old? I have Sicma 72" finish mower that used to work to work great at my old place but I haven't used it for quite a few years. I bought the mower new. Now it seems that even if I tighten the belt it just stretches and starts slipping again. It doesn't even make the tractor work (MF 135 diesel). The other thought is the sides of the belt that grip are just worn too much to properly grip the pulley. The belt seems to fit fairly deep in the pulleys. Maybe new belts is all I need? Any insight would be much appreciated.

 

[Poopdeck Pappy]

Yep, belts can stretch to the point where they're not tight enough, and can also wear so they don't sit properly in the pulley as you have noticed on yours. I'd bet that a new belt will fix you right up.