Park brake won't hold. mower will roll with brake engaged

If it was like it from day 1, you should have claimed on the warranty. Any warranty left on it? It is likely is just needs the brake cable adjusting.

Engaging The Parking Brake - Ryobi RM480e Original ...

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ENGAGING THE PARKING BRAKE · 1. Place the direction control switch in the. neutral (N) position. · 2. Step on and hold the brake pedal. · 3. Lift and hold the ...

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Starting instructions per manual.

1. Make sure bypass rod is pushed in.
2. Sit in seat.
3. Make sure mower is disengaged. (See Engaging and Disengaging Mower in the OPERATING section.)
4. Lock the park brake.
5. For automatic models, put transmission shifter into center slot.
6. Parking brake - ON

If it still doesn't crank, cycle the safetys.

1. Parking brake - OFF/ON
2. PTO - ON/OFF
3. For automatic models, move shifter out of center slot then back.
4. Seat switch - Rise from seat then sit firmly.

If still no crank, check battery charge is at least12.5VDC. If battery ok, then likely a safety switch has failed or misaligned. Try rotate and hold ignition switch at start position and see if moving safeties allows crank. Move out/in seat, pull PTO switch on push off, move brake to off then back on. Other possible causes include fuse, ignition switch, relay, poor circuit continuity (power, control, or ground).

If new to the unit...

To set parking brake, you FULLY depress and hold the brake/clutch pedal, engage and hold park brake lock, release brake/clutch pedal. You may need to adjust seat forward.

Else...
If the brake lock won't move when brake/clutch is fully depressed, check for obstruction in brake lock linkage.

brake needs to be tightened up , id almost bet that service brake is a bit loose as well , Jd's use a disk shoe on transmission side that has a simple disk brake shoe on it , have a look at it there's a bolt right on side of it to tighten it up , Less is better on these , don't make it drag as it will heat up and wear down even faster

Adjustment needed

are you holding the lever while lifting your foot of the pedal?

you need to hold the lever until the pedal is released

look at sears parts online

if your not experience with brakes i won,t attempt replacing the cable. if you always have a freezing problem use a wheel chuck.
it,s a wedge u put against the tire so a car won,t roll