I have a MTD yard machine and the mower blades will engage but won't disengage. Any help on what could be wrong would be appreciated.

I have a murray 12hp 38" mower but the blades won't engage.I have replaced the belt and blades still won't engage.Any help on what could be wrong?

Sounds As Though You Need To Look At The Deck And Where You See The Pulleys In The Center , Spray A Good Quality Lubricant On The Arm And Try And Move It, You Could Also Have A Spring Missing, Or Disconnected.