:welcome:
Nice job.
The brake has two adjustments.
The bolt in the center of the actuating rod ( the bit that pushes on the pins) is the brake adjustment.
Tighter = harder
On the rod connected to the pedal is an adjuster nut and spring.
You use this to adjust when the brake gets applied with respect to the clutch being applied so you are not declutching while you are braking.
go to
http://www.mymowerparts.com/pdf/MTD-Service-Repair-Manuals/ and download your manual.
The Must have book 3 or the 700 series depending upon your model umber which you have not supplied which makes giving acurate & detailed information difficult.
OR you can google Must have book 1 lawn tractors and see if you can find one on the web
MTD used funny size belts and generally blades not stopping is because the belt is too tight or the blade brakes are beyond use as the pads wear and the spring looses its tension.
When adjusted properly the brake should have about .100" to .050" clearance from the pulley.