Parts for 21AA404B031 — MTD

We found 55 parts confirmed to fit the MTD 21AA404B031.

Compatibility table

Prices shown are an informational reference range only, not an offer or an Amazon price — RepairKitHub does not sell parts directly. Each part links to an Amazon search so you can compare current listings yourself.

Common failure areas on this model

The confirmed parts above group into a handful of failure areas. Here is what each points to and how to check it before you order anything.

Storage, trim and cosmetic hardware

Symptom: A cracked shelf, broken door bin, worn hinge, or missing trim piece -- cosmetic and storage wear rather than a functional breakdown.

Check: Match the physical dimensions and mounting tabs of the old part before ordering; these pieces are often model-specific even between visually similar models.

Parts in this group on 21AA404B031: 78604345 (LH HANDLE BRACKET), 78604356A0638 (BRACKET-DEPT), 7860113A0638 (Shield), 91804435 (Cover Bearing), 78604357A0638 (BRACKET-CABL), 73106253B (Cover), 7101238 (Lawn & Garden Equipment Screw), 73804320 (Lawn & Garden Equipment Shoulder Screw), 94104299 (Lawn Tractor Mandrel Shaft Spacer), 78604358 (Return Bracket), 786043630638 (Tail Bracket), 786043640638 (Tail Bracket), 686040980638 (Handle Assembly), 7200278A (Ryobi Tiller Handle Grip), 7500885A (Ryobi Tiller Spacer), 786043430638 (Troy-Bilt Bracket-Idle), 78604346 (Troy-Bilt Bracket-Idle), 7860340B (Yard Machines Tiller Handle Adjustment Rod), 73204276A (MTD Lawn Tractor Spring), 7100599 (MTD Lawn Tractor Screw).

General hardware and mounting parts

Symptom: A small mechanical or mounting part has failed, cracked, or gone missing.

Check: Compare the physical shape and mounting points to the original piece, and confirm the exact part number against your model plate before ordering.

Parts in this group on 21AA404B031: 642040710638 (Tiller Tine Assembly, Left), 786043600638 (Bumper), 642040720638 (Tiller Tine Assembly, Right), 7100170 (Lawn & Garden Equipment Bolt), 94104298 (Lawn Tractor Mandrel Bearing), 786041040638 (Depth Drive Bar), 72104271 (Plug), 7470432 (Ryobi Tiller Rear Guard Connecting Rod), 7160204 (Tiller Retainer Ring), 72104232 (Tiller Tine Shaft Oil Seal), 91804815A (Tiller Transmission Assembly), 74804087A (Tiller Washer), 7320614 (Tiller Wire Ring), 91704381 (Tiller Worm Gear), 7413114 (Troy-Bilt Bearing-Ball), 7200270A (Reverse Grip), 91105028 (Worm Shaft), 55073 (Drag Bar-tuf), 94604506 (Tiller Forward Drive Control Cable), 94604504 (Tiller Reverse Cable), 91704380 (Tiller Tine Input Sprocket Assembly), 7140143A (Tiller Click Pin), 7120421 (Tiller Wing Nut), 9360119 (MTD Lawn & Garden Equipment Lock Washer), 71204063 (Yard Machines Lawn & Garden Equipment Lock Nut, 5/16-18), 71204065 (MTD Yard Machines Lawn Tractor Flange Nut).

Drive system (belts, pulleys, motors)

Symptom: A drum or tub that won't turn, a burning-rubber smell, or a loud thump or squeal during a cycle.

Check: With power off, turn the drum or tub by hand -- resistance or grinding points to the motor or a bearing, and a cracked, glazed, or snapped belt is visible once the cabinet is open.

Parts in this group on 21AA404B031: 73106529 (Tiller Belt Cover), 75604355 (Tiller Transmission Pulley), 78604312 (Idler Bracket), 1916658 (Reverse Belt), 1916657 (Belt), 68404168 (Tiller Idler Pulley), 95404091 (Belt-v Rev Drv 3), 95404090 (Tiller Forward Drive Belt), 7560625 (MTD Lawn Mower Roller Wheel).

Before you buy

Match 21AA404B031 exactly against the model and serial plate on the appliance itself before ordering anything — a single mismatched character can point to a different production run with different parts. Then check the part number printed or stamped on the part you are replacing against the part numbers in the table above; the printed number is the most reliable way to confirm fitment when a model has gone through multiple production runs. RepairKitHub does not sell parts directly — every part link above routes to an Amazon search for that part number so you can compare current listings and sellers yourself.

How to confirm this is your model

Check inside a door opening, on a back or side panel, or behind a removable panel or drawer for a label printed with the model and serial number. Match every character exactly, including letters and dashes at the end — appliance model numbers often have similar prefixes but different suffixes for different production runs.

Still not sure?

Use the model lookup tool to search by model or part number, or start from the symptom your appliance is showing.