yeah, you need to replace the shoe when you cannot ENGAGE your clutch at all........just helped 1 of the MRX4 guy to figure that part out, he cannot get the clutch engage evern the spring nut is 1 turn from the outside thread...replaced the shoe, clutch engaged wth just a little bip....
For Pro racer...replace clutch shoe every 30 minutes of usuage.....for cheap ass like myself...I replaced mine like every 2 race day....cause I am no where near to the PRO level yet.