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MTD
Gas Walk-Behind Mower

Model # 12A-44MZ255 Official MTD lawn mower

Here are the diagrams and repair parts for Official MTD 12A-44MZ255 lawn mower, as well as links to manuals and error code tables, if available.

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Not all parts are shown on the diagrams—those parts are labeled NI, for “not illustrated”.

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Owner’s manual
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Model diagram and schematic

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Showing 10 of 105 parts  |
Blade-21" Mu 742-0741
#24

Lawn mower diagram

Blade-21" mu

Part #742-0741

Replaced by #942-0741A

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Manufacturer substitution
This part replaces 742-0741. Substitute parts can look different from the original.
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Yard Machines Lawn & Garden Equipment Nut 712-04064
#21

Lawn mower diagram

Yard machines lawn & garden equipment nut

Part #712-04064

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$4.49 | 
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Knob 720-04072
#9

Lawn mower diagram

Knob

Part #720-04072

Replaced by #720-04072A

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Manufacturer substitution
This part replaces 720-04072. Substitute parts can look different from the original.
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Lawn Tractor Screw, 1/4-20 X 5/8-in (replaces 910-1652) 710-1652
#42

Lawn mower diagram

Lawn tractor screw, 1/4-20 x 5/8-in (replaces 910-1652)

Part #710-1652

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Wing Nut 712-0397
#38

Lawn mower diagram

Wing nut

Part #712-0397

Replaced by #712-0397A

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Manufacturer substitution
This part replaces 712-0397. Substitute parts can look different from the original.
This item is not returnable
$5.22 | 
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Cable Tie 726-0240
#11

Lawn mower diagram

Cable tie

Part #726-0240

Replaced by #726-0178

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Manufacturer substitution
This part replaces 726-0240. Substitute parts can look different from the original.
This item is not returnable
$2.16
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Lawn Mower Screw 710-04531
#60

Lawn mower diagram

Lawn mower screw

Part #710-04531

This item is not returnable
$7.77 | 
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Grsbg 21" 40 664-04007
#8

Lawn mower diagram

Grsbg 21" 40

Part #664-04007

Replaced by #964-04007A

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Manufacturer substitution
This part replaces 664-04007. Substitute parts can look different from the original.
$143.25 | 
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V-belt 754-0637A
#51

Lawn mower diagram

V-belt

Part #754-0637A

Replaced by #954-0637A

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Manufacturer substitution
This part replaces 754-0637A. Substitute parts can look different from the original.
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Bail 747-1161A
#1

Lawn mower diagram

Bail

Part #747-1161A

Replaced by #747-1161A-0637

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Manufacturer substitution
This part replaces 747-1161A. Substitute parts can look different from the original.
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$20.10 | 
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Symptoms for gas walk-behind mowers

Choose a symptom to see related walk-behind mower repairs.

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Why does my lawn mower run rough?

Main causes: engine needs tune up, dirty or clogged carburetor, damaged flywheel key…

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Why does my lawn mower cut unevenly?

Main causes: uneven wheel height settings, damaged wheel, dull or damaged cutting blade…

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Why does my lawn mower vibrate a lot?

Main causes: damaged cutting blade, loose cutting blade, damaged flywheel key, engine needs tune up…

Read more

Why won't my lawn mower start?

Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, ba…

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Why does my lawn mower stall?

Main causes: dirty carburetor, bad spark plug, clogged air filter, engine choke problems, clogged gas cap vent…

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Why won't my lawn mower move?

Main causes: drive control cable failure, worn or broken drive belt, bad transmission, broken drive wheel…

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Repair guides for gas walk-behind mowers

These step-by-step repair guides will help you safely fix what’s broken on your walk-behind lawn mower.

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How to replace a lawn mower spark plug

How to replace a lawn mower spark plug

Take a few minutes to replace the spark plug during your lawn mower's annual tune-up or if the spark plug is burnt or cr…

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Repair difficulty
Time required
 15 minutes or less
How to replace a lawn mower blade

How to replace a lawn mower blade

Check your lawn mower blade regularly and replaced it if it's bent or damaged. …

Read more
Repair difficulty
Time required
 15 minutes or less
How to replace a lawn mower flywheel key on a flathead engine

How to replace a lawn mower flywheel key on a flathead engine

When you hit a hard object with your mower, the flywheel can shear to protect more expensive components. Learn how to re…

Read more
Repair difficulty
Time required
 45 minutes or less

Effective articles & videos to help repair your walk-behind mowers

Use the advice and tips in these articles and videos to get the most out of your walk-behind lawn mower.

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How to enjoy all the online benefits we offer on our Sears PartsDirect website

How to enjoy all the online benefits we offer on our Sears PartsDirect website

Learn about all the convenient features on our Sears PartsDirect website that make your parts purchases easier.…

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Introducing new technical repair content that we’re developing for the Sears Technical Institute

Introducing new technical repair content that we’re developing for the Sears Technical Institute

Learn about Sears Technical Institute and the advanced technical content being developed for aspiring appliance techs.…

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Top questions about Sears and Sears PartsDirect

Get answers to frequently asked questions about Sears and Sears PartsDirect.…

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