:confused: :rolleyes: I have a 1994 murray rider lawn mower that I can not disengage mower blades? Model 3912-030 12 hp/39" deck/ the blades are engaged all the time / i have checked belt looks good / i have done some belt adjusting/ i have changed the mower deck engagement spring /mower starts only when i move engagement lever towards disengage position but goes back to engage position / however i can still cut grass "safety issue though " please advise/ thanks lou

You have an idler pulley problem, or a blade brake problem. You do not indicate if the blades are turning fast when disengaged or not, so it is kind of hard to pick which is the problem.