This DIY riding mower repair guide gives step-by-step instructions for replacing a mandrel assembly on a riding lawn mower. The mandrel assembly attaches to the deck and spins the blade. The bearings in the mandrel assembly wear down through normal use. An unbalanced blade speeds the wear on the bearings, as does hitting rocks while mowing. The mandrel assembly in this repair guide includes the blade shaft and bearings. Other mandrel assemblies can include different parts, so check the parts diagram for your mower for a complete list of parts included in the mandrel assembly (enter the model number above to find the diagram). Replace the mandrel assembly with a manufacturer-approved replacement part if the blade shaft vibrates or doesn't spin freely inside the mandrel.
Use this repair guide and video to help you replace a mandrel assembly in common Craftsman, MTD, Troybilt, Husqvarna, Ariens, Cub Cadet and Snapper riding lawn mowers and lawn tractors.
This video explains how to replace a mandrel assembly on a riding lawn mower.
Disconnect the spark plug
Park the tractor on a level surface and set the parking brake.
Turn the ignition switch off and remove the key.
Wear work gloves to protect your hands.
Lift the tractor hood and disconnect the spark plug wire.
Disconnect the spark plug.
Remove the mower deck
Lower the mower deck to its lowest position.
Disengage the cutting blades.
Roll the blade belt off the engine pulley and release the belt from the belt keepers.
Remove the front lift link support retaining pin and washer and then detach the support from the deck.
Remove the left suspension arm retaining clip and washer and then detach the arm from the tractor frame.
Remove the left rear deck bracket retaining clip and washer and then release the bracket from the deck.
Repeat the process on the other side of the deck to disconnect the right suspension arm and right rear deck bracket.
Pull the deck out far enough to access the blade cable attached to the deck.
Release the locking tabs and pull the blade cable out of the deck bracket.
Disconnect the blade cable spring from the idler arm and move the cable aside.
Pull the deck out from under the frame.
Pull out the mower deck.
Remove the mandrel assembly
Put a wood block between the blade and mower deck to keep the cutting blade from moving.
Remove the pulley mounting nut and detach the pulley.
Pull out the wood block and flip the mower deck over.
Put the wood block back in place.
Remove the blade mounting bolt and pull off the cutting blade.
Remove the wood block and flip the deck upright.
Remove the mandrel mounting bolts and pull the mandrel out from under the deck.
Remove the mandrel bolts.
Install the new mandrel assembly
Thread the mandrel mounting bolts into the new mandrel to thread the mounting holes and then remove the bolts.
Position the new mandrel assembly in the deck opening and install the mounting bolts. Tighten the bolts firmly.
Put the wood block between the blade and mower.
Reinstall the pulley on the new mandrel assembly with the blade belt properly attached to the pulley. Tighten the mounting nut firmly.
Remove the wood block and flip the deck over.
With the correct side of the blade facing up, attach the blade to the new blade shaft and hand tighten the blade bolt.
Put the wood block back in place and tighten the blade bolt firmly.
Remove the wood block and flip the deck upright.
Reinstall the pulley.
Reinstall the mower deck
Push the deck near the tractor frame.
Connect the blade clutch cable spring to the idler arm.
Push the blade clutch cable retainer into the deck bracket and engage the locking tabs.
Position the deck under the tractor frame.
Reconnect the front lift link support to the deck using the washer and retaining clip.
Reconnect the left suspension arm and deck bracket using the washers and retaining clips.
Repeat the process to reconnect the right suspension arm and deck bracket.
Route the blade belt through the belt keepers and roll the blade belt onto the engine pulley.
Check the blade belt routing on the mower deck and adjust the blade belt if needed to route the belt over all pulleys and through all belt keepers.
Reinstall the mower deck.
Reconnect the spark plug
Reconnect the spark plug wire and lower the tractor hood.
These step-by-step repair guides will help you safely fix what’s broken on your riding mower or lawn tractor.
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