Thanks for the info Digger, I have checked the deck suspension out, it's a complicated setup but everything is straight and aligned, and nothing moves that shouldnt.
The mule pulleys, with the recent belt installed, were free and clear of any obstructions, the left pulley was Id say about 1 3/4" from the front axel, and the belt had good tension. The belt prior to that one I beleive was too short and the pulley rubbed into the front axel a bit..but the recent one was fine in that respect.
Both bearings feel smooth, no grittyness or slop.
The root problem just seems to be the wicked angle the belts have to turn at the mule drive.
However on my Deere 316 with a nearly identical PTO setup, the belt lasts 300-400 hours, and it's jsut a cheapy Napa 4L Blade Runner belt.
My Wheel Horse tractors run a slightly different routing, but still put the belt under all sorts of twists and turns, and I have yet to tear one up, but they doo stretch to the max adjustment.
The cub just likes to eat belts. But the belt that came on it lasted a very long time...which is what throws me off.
Ive got a shop full of vintage and Early Garden tractors from 1962 to a Late 80's Mitsubishi Diesel..and the cub is the only one that eats belts.
I do have to say though that the drive setup is super slick now that I got the vibrations out of it. Wish the clutch would bite harder in 3nd and 3rd, If im trying to pull something that is stuck it just slips bogs the engine a little and slips the clutch..of which all plates and discs, springs are basically new.
IS the 1/2"X 77.5" belt the right size belt? I checked the previously mentioned site and I think that is the belt for a 44" deck on a quiet line Cub.