1999-2002 TRX400EX Fourtrax Service Manual, Page 189Get this manual
REAR WHEELSUSPENSION Install the driven sprocketwith the chamfered side of the bolt holes facing inCoat new O-ring with oil and install it between the driven sprocket flange and axle
Install the axle into the swingarm through the drive chain until it is fully seatedInstall the chain over the driven sprocket
AXLECoat new O-ring with oil and install it into the groove in the disc hubApply grease to the disc hub splinesInstall the brake dischub onto the axle with the stamp facing outInstall the inner and outer lock nuts onto the axleInstall the stopper ring but do not install it into the ring groove yet