MTD Yardman 46" wont stop. Its manual

[Per Hansen]

I got this mower and the brakes didn't work, but I found they actually do, but the belt doesn't disengage properly, it will be on or of. I've removed the deck and lifted the front up to vertical, and the belt is lose so I can turn the engine pulley by hand. Nothing seems wrong, but on the ground, one moment in forward it goes pressing the brake does nothing, hitting the right pedal may disengage and the brakes will work, but I never know what its going to do. Disengaged it can make a rattling sound, which I think is the belt trying to grab. I asked previous owner re. brakes answer was they never really worked. He did roll down a hill caused by this and gave it to me. I've searched and asked questions but no answers. Hopefully someone here can help me out.

 

[bertsmobile1]

Please post the model number from the plate under the seat
There are quite a few variations to his mower ver it's 20 year run.

 

[Per Hansen]

Previous owner changed all the belts to B-belts and because I found a split in the main drive belt I changed both belts to the right part number, it all works now, except it's a bit jerky. Thanks