OK now you have me confused.
I gather this is the same mower as in our previous post with the short drive belt ?
From the top there is no emergency brake,
There is a brake combined with the clutch and a latch to allow you to use it as a parking brake.
IF you have the clutch now releasing the belt enough to allow it to slip on the engine pulley the next thing is to adjust the brake.
Well in your case I would remove the brake and have a good look at the brake pads.
Remove the right wheel and you will see it staring you in the face.
The two bolts either side of the saddle hold it to the gearbox,
The center nut is the adjustment
The lever is a cam and presses two pins down onto the front brake pad onto the brake disc.
The disc sits on a spline so it is a floating disc and when the brake pad pushes on it it moves back and presses against the rear pad.
Crud builds up around the disc preventing it from working and the pins can rust solid.
Go to the same JD web page and print out the brake parts break down to ensure all the bits are there.
Pads are a service item and discs can also need replacing particularly if the brake has been dragging for a long time.
The rod that operates the brake also has an adjustment.
This is for timing only and some twits crank this up to make the mower stop better,
Its job is to adjust when the brake is applied, not how hard and the idea is the brake lever does not activate the brake till after the clutch has dissengaged the drive belt otherwise the brake will be working against the engine and in time it will damage the input gear on the transmission.