Zero-turn riding mowers operate with a zero turning radius, cutting so close to trees and other obstacles that little follow-up trimming is required. Most can pivot a full 180 degrees without leaving behind any uncut grass. All zero-turn mowers are rear-wheel drive. The wheels are independently powered by a hydrostatic transmission, and steering is controlled by a pair of joysticks that regulate the speed of each wheel. Models such as the Toro Commercial Z Master series use a single drive belt to operate the twin blades in the cutting deck. The belt is tensioned by a spring-loaded idler arm. Belt slippage caused by insufficient tension may result from a weak idler spring.
Disengage the Power Take Off lever, move the control joysticks to the neutral locked position and engage the parking brake.
Turn off the engine and remove the key. Allow all moving parts to stop before continuing.
Lower the cutting deck to the 3-inch height.
Remove the belt cover on top of the cutting deck by raising the latch and sliding the cover forward.
Locate the 1/2-inch square ratchet hole in the spring-loaded idler arm. Insert a 1/2-inch ratchet drive into the hole and rotate the idler arm clockwise to slacken the drive belt.
Slip the drive belt off the main cutter blade pulleys. Unscrew the nut securing the belt guide to the idler arm pulley and remove the belt.
Unhook one end of the idler spring from the grooved bolt between the blade pulleys and the other end from the attachment point on the back of the idler arm.
Install a new idler spring by hooking one end over the grooved bolt, then hooking the other end to the attachment point on the back of the idler arm.
Reinstall the belt on the main cutter blade pulleys. Rotate the idler arm clockwise with the ratchet drive and slip the belt over the idler pulley.
Allow the spring to pull the idler arm back to its home position so the idler arm tensions the drive belt. Reinstall the belt guide on the idler pulley.
Slide the belt cover back into place. Press the latch down to lock it.