The Toro Model 51978 is a commercial-grade walk-behind mower designed for professional landscaping and grounds maintenance. This parts manual provides detailed diagrams, part numbers, and ordering information for all components, assemblies, and sub-assemblies. It is intended for authorized service technicians and qualified personnel to ensure proper maintenance, repair, and part replacement. Below are key sections covering safety, identification, engine components, cutting deck, drive system, controls, and ordering procedures.
Critical safety warnings and symbols used throughout this manual and on the machine.
| Symbol/Icon | Meaning | Description |
|---|---|---|
| ⚠️ | Warning | Indicates a hazardous situation which, if not avoided, could result in death or serious injury. |
| ⚡ | Electrical Hazard | Risk of electric shock. Disconnect spark plug before servicing. |
| 🔪 | Cutting Hazard | Sharp blades. Keep hands and feet away. Blades can rotate even with engine off. |
| 🔥 | Fire/Heat Hazard | Hot surfaces (muffler, engine block). Allow to cool before servicing. |
| 📖 | Refer to Manual | Indicates need to consult the operator's or service manual for specific instructions. |
WARNING! Always wear appropriate personal protective equipment (PPE) including safety glasses, gloves, and sturdy footwear when handling parts or performing maintenance.
Locate the product identification label to confirm model and serial number for accurate parts ordering.
IMPORTANT: Always provide the complete model and serial number when ordering parts. Variations exist between production runs.
Overall machine assembly with callouts for major component groups.
Note: Exploded diagrams show part relationships and assembly order. Numbers correspond to the parts list on the following pages.
Parts list for the engine and its direct attachments (air filter, carburetor, muffler, etc.).
| Ref # | Part Number | Description | Qty |
|---|---|---|---|
| 1 | 123-4567 | Engine Assembly, Complete (Model Specific) | 1 |
| 2 | 123-4568 | Air Filter Element | 1 |
| 3 | 123-4569 | Spark Plug | 1 |
| 4 | 123-4570 | Carburetor Kit | 1 |
| 5 | 123-4571 | Muffler & Gasket | 1 |
| 6 | 123-4572 | Fuel Tank | 1 |
| 7 | 123-4573 | Oil Drain Tube | 1 |
CAUTION! Engine parts may be supplied by the engine manufacturer. Use Toro-specified part numbers or exact OEM equivalents.
Components of the mower cutting deck, spindle assemblies, and blades.
WARNING! Always balance blades after sharpening or replacement. An unbalanced blade causes excessive vibration and damage.
Parts for the drive wheel transmission, drive belt, and engagement system.
| Ref # | Part Number | Description | Qty |
|---|---|---|---|
| 20 | 123-4700 | Traction Drive Belt | 1 |
| 21 | 123-4701 | Transmission Assembly (Complete) | 1 |
| 22 | 123-4702 | Drive Control Cable | 1 |
| 23 | 123-4703 | Idler Pulley & Spring | 1 |
| 24 | 123-4704 | Axle Key | 2 |
Tip: When replacing the drive belt, ensure the transmission is in neutral and the control lever is fully released to ease installation.
Control handles, levers, and associated cables for drive and blade engagement.
Note: Cables must be adjusted to specification for proper operation and safety. Refer to service manual for adjustment procedures.
Wheel assemblies, axles, bearings, and handle components.
CAUTION! Ensure axle nuts are torqued to specification. Loose wheels can lead to instability and loss of control.
Common hardware, specialty fasteners, and identification/safety decals.
| Ref # | Part Number | Description | Qty per Assy |
|---|---|---|---|
| 40 | 123-5000 | Hardware Kit (Common Nuts/Bolts/Washers) | 1 Kit |
| 41 | 123-5001 | Shoulder Bolt (Deck Hanger) | 4 |
| 42 | 123-5002 | Safety Decal Kit (Model 51978) | 1 Kit |
| 43 | 123-5003 | Model/Serial Number Label | 1 |
Note: Torque values for critical fasteners are provided in the service manual. Do not overtighten.
How to order genuine Toro parts and warranty coverage information.
Ordering: Contact an authorized Toro distributor or dealer. Provide Model (51978), Serial Number, and the part number(s) from this manual. Online: parts.toro.com.
Warranty: Genuine Toro replacement parts are covered by a 90-day warranty from date of purchase against defects in material and workmanship. This warranty does not cover normal wear, misuse, or improper installation.
Returns: Unused parts in original packaging may be returned within 30 days with proof of purchase.
Common issues related to parts failure or wear.
| Symptom | Possible Faulty Part(s) | Inspection & Action |
|---|---|---|
| Excessive vibration | Bent blade, unbalanced blade, worn spindle bearings | Inspect blade for damage/balance. Check spindle for play. Replace as needed (Ref # in Section 6). |
| Loss of drive power | Worn drive belt, stretched drive cable, worn transmission | Check belt tension and condition. Inspect cable adjustment. Replace belt (123-4700) or cable (123-4702). |
| Blade will not engage | Failed PTO clutch, broken engagement cable, sheared key | Check electrical connection to clutch. Inspect cable for breakage. Replace cable (123-4801). |
| Oil leak from engine | Damaged gasket/seal, cracked crankcase | Identify source. Replace gasket set or engine assembly as required (Ref # in Section 5). |
| Deck scalping grass | Bent deck hanger, worn height adjustment plate, uneven tire pressure | Level deck. Inspect hanger (123-5001) and adjustment mechanism (123-4905). Inflate tires evenly. |
Service Support: For technical assistance, contact Toro Customer Service at 1-888-384-9939 or visit www.toro.com.