How to replace a lawn mower drive belt

This lawn mower repair guide has step-by-step instructions on how to replace a lawn mower drive belt. The mower won't move with a broken or worn drive belt. Replace the drive belt with a manufacturer-approved lawn mower part if it's worn or broken.

This drive belt replacement procedure works for common Craftsman, Toro, Troybilt, MTD, Husqvarna, Poulan, Murray and Ariens front-wheel drive walk-behind lawn mowers.

A drive belt problem is just one reason the wheels of a lawn mower won't drive forward. To learn how to diagnose a lawn mower drive problem, see Lawn Mower Won't Move Troubleshooting Video: Motion Drive Failure.

Instructions

1. Disconnect the spark plug wire

Disconnect the spark plug wire from the spark plug.

2. Remove the blade

Remove the fuel tank cap.

Place a plastic bag over the fuel tank opening and reinstall the fuel tank cap to prevent gasoline from leaking out through the fuel tank cap vent.

Tilt the mower back to lift the front wheels then secure the mower handle to your worktable to hold the mower steady. Remove the bottom drive cover mounting screws.

Wedge a block of wood between the mower blade and the deck to keep the blade from turning when you loosen the blade nut.

Loosen and unthread the blade nut while holding the cutting blade to keep the blade from falling.

Pull the blade, blade support and blade nut off the crankshaft.

Remove the debris shield mounting screws and pull off the debris shield.

Roll the drive belt off the crankshaft pulley.

Pull the crankshaft pulley off and free the belt from the crankshaft.

Release the clamp from the mower handle and lower the mower to the upright position.

Remove the top drive cover mounting screws.

Release the height adjuster lever and pull the drive cover off.

Pull off the belt keeper from the top of the transmission.

Release the drive belt from the transmission pulley and remove the drive belt.

Tip: If you have the mower on the ground instead of a worktable, tilt the lawn mower on its side with the air filter up to access the mower blade.

3. Remove the drive belt

Remove the bottom drive cover mounting screws.

Remove the debris shield mounting bolts and pull off the debris shield.

Roll the drive belt off the crankshaft pulley.

Pull the crankshaft pulley off and free the belt from the crankshaft.

Release the mower handle and lower the mower to the upright position.

Remove the top drive cover mounting screws.

Release the height adjuster lever and pull the drive cover off.

Pull off the belt keeper from the top of the transmission.

Release the drive belt from the transmission pulley and remove the drive belt.

4. Install the new drive belt

Push the drive belt through the deck opening and install the new drive belt on the transmission pulley.

Reinstall the belt keeper on the transmission.

Insert the drive cover tab into the deck slot by the engine and position the drive cover on the deck tray.

Reconnect the height adjuster lever to the drive cover.

Reinstall the top drive cover mounting screws.

Tilt the mower back to lift the front wheels, then clamp the mower handle to your worktable to hold the mower steady.

Route the drive belt over the crankshaft.

Align the crankshaft pulley shaft indentions with the crankshaft slot and slide the pulley onto the crankshaft.

Roll the drive belt onto the crankshaft pulley.

Push the debris shield tab through the deck opening and reinstall the debris shield.

Reinstall the debris shield mounting bolts.

Reinstall the bottom drive cover mounting screws.

5. Reinstall the blade

Position the blade, blade support and blade bolt on the crankshaft and hand-tighten the blade bolt on the crankshaft. 

Wedge a block of wood between the mower blade and the deck to keep the blade from turning when you tighten the blade bolt. 

Tighten the blade bolt to 500 in.-lbs. using a torque wrench. 

Remove the wood block. 

Release the mower handle from the worktable and lower the mower to the upright position. 

Remove the plastic bag from the fuel tank opening and reinstall the fuel tank cap.

6. Reconnect the spark plug wire

Push the spark plug wire back onto the spark plug.