Help have older craftsman rider.brakes good but wont stop

Hi, i have a 16 hp 42" craftaman lawn tractor. It was not stopping so i took the caliper apart and looked at the pads
They are still good.. When i push the brake the pads grab the puck firmly so ot can not ne turned, but the wheels will
Still rotate. Does anyone have an idea of wht this might be? Thanks
In advance.

The brake works on the LAYSHAFT not the main shaft thus locking the diff
This means that one wheel can only turn foreward and the other can only turn backwards so when it is on the ground it either goes nowhere or turns very very tight circles.
In the middle of the lever that pushes on the two little pins is an adjuster nut.
In for harder braking
Out for looser braking.
The rod that activates the lever also has an adjustment on it.
That is used to adjust the breaking against the clutching so the mower is not trying to drive & brake at the same time.