a suspension system for the rear axle of a self - propelled agricultural windrower . the axle is split into two components , each having an air spring to absorb shocks . the two air springs are interconnected by a tube to equalize the internal pressure . a pair of pins can be inserted through the respective axle components and a structural member of the tractor to fix the components relative to the unit structure , thereby incapacitating the suspension and permitting effective steering of the tractor in the absence of a header .