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John Deere 3720 Manual: A Comprehensive Guide

Understanding Your John Deere 3720

Model Overview and Specifications

The John Deere 3720 is a compact utility tractor designed for a wide range of tasks, from mowing and landscaping to light agricultural work. This robust machine is known for its reliability, versatility, and user-friendly design. It's important to understand its key features and specifications to ensure you're operating it safely and effectively. The 3720 typically features a powerful diesel engine, providing ample horsepower for various implements and attachments. Familiarize yourself with the engine's specifications, including its horsepower rating, fuel consumption, and recommended maintenance schedule, as this will directly impact the tractor's performance and longevity.

Understanding the hydraulic system of your John Deere 3720 is crucial for operating implements such as loaders, backhoes, and mowers. The hydraulic system provides the power to lift, lower, and control these attachments, allowing you to perform a variety of tasks with ease. Knowing the hydraulic system's capacity, pressure settings, and fluid type is essential for proper operation and maintenance. Refer to the specifications chart in this manual to ensure you are using the correct fluids and operating within the recommended parameters. Proper hydraulic system maintenance will prevent costly repairs and ensure optimal performance of your implements.

The transmission and drivetrain of the 3720 are designed to provide smooth and efficient power delivery to the wheels. Depending on the specific model and year, your tractor may have a hydrostatic transmission or a gear-driven transmission. Understanding the operation and maintenance requirements of your transmission type is essential for maximizing its lifespan and preventing premature wear. Regular inspection of the drivetrain components, such as the axles, gears, and bearings, is also crucial for identifying potential problems early on. Proper lubrication and timely repairs will ensure that your 3720 continues to deliver reliable performance for years to come.

Safety Precautions and Guidelines

Operating a tractor, even a compact one like the John Deere 3720, requires a strong understanding of safety precautions and guidelines. Before operating the machine, thoroughly read and understand the operator's manual, paying particular attention to the safety warnings and instructions. Always wear appropriate personal protective equipment (PPE), including safety glasses, hearing protection, and sturdy footwear. This equipment helps to minimize the risk of injury in the event of an accident. Prioritize safety at all times, and never take shortcuts or operate the tractor if you are fatigued or under the influence of alcohol or drugs.

When operating the John Deere 3720 on uneven terrain or slopes, exercise extreme caution to prevent rollovers. Rollovers are a leading cause of tractor-related fatalities, so it's crucial to be aware of the risks and take steps to mitigate them. Avoid operating the tractor on steep slopes whenever possible, and always drive slowly and deliberately. Consider installing a rollover protection structure (ROPS) and wearing a seatbelt to provide additional protection in the event of a rollover. Remember, preventing a rollover is always better than trying to survive one.

Always perform a pre-operation inspection of your John Deere 3720 before each use. Check the fluid levels, tire pressure, lights, and all other critical components to ensure they are in good working order. Inspect for any signs of leaks, damage, or wear, and address any issues before operating the tractor. Regular inspections can help you identify potential problems early on, preventing costly repairs and ensuring safe operation. Taking a few minutes to inspect your tractor before each use can save you time, money, and potentially even your life.

Operating Procedures

Pre-Operation Checks and Inspections

Before operating your John Deere 3720, a thorough pre-operation check is crucial for safety and to prevent potential mechanical issues. Begin by visually inspecting the tractor for any signs of damage, such as leaks, cracked hoses, or loose components. Check the fluid levels, including engine oil, coolant, hydraulic fluid, and fuel, ensuring they are within the recommended ranges. Inspect the tires for proper inflation and any signs of wear or damage, which are paramount for optimal traction and stability. Don't overlook the lighting system, testing headlights, taillights, and turn signals to ensure they are functioning correctly, especially if operating in low-light conditions. Finally, inspect and test the brakes to make sure that they are in proper working order. Continuing with your pre-operation checks, examine the condition of the air filter and clean or replace it as necessary, as a clean air filter is vital for engine performance and longevity. Inspect the battery terminals for corrosion and ensure they are securely connected, which helps prevent starting issues. Examine all safety devices, such as seatbelts and ROPS (Rollover Protective Structure), confirming they are in good working order and properly adjusted. Check all guards and shields are securely in place, particularly around moving parts, to protect the operator from potential hazards. Remember, a few minutes spent on pre-operation checks can save you from costly repairs and, more importantly, ensure a safe and productive operation.

Starting and Stopping the Engine

Starting the John Deere 3720 engine requires a systematic approach. First, ensure the transmission is in neutral and the parking brake is engaged, crucial safety precautions to prevent accidental movement. Turn the key to the "on" position and wait for the glow plug indicator to illuminate if the engine is cold, allowing the glow plugs to warm the cylinders for easier starting. Once the glow plug indicator goes off, turn the key to the "start" position and hold it until the engine starts, but do not engage the starter for more than 30 seconds at a time to avoid overheating the starter motor. If the engine fails to start, wait a minute before attempting again, this allows the battery to recover. After the engine starts, let it idle for a few minutes to allow the oil to circulate and warm up before putting it under load. When stopping the engine, avoid immediately shutting it down after heavy use. Allow the engine to idle for a few minutes to cool down, which prevents overheating and extends the life of the engine components. Turn the key to the "off" position to shut down the engine, which will stop the engine. After shutting down, inspect the engine compartment for any signs of leaks or unusual noises, which could indicate potential problems. Finally, remove the key to prevent unauthorized operation and engage the parking brake to ensure the tractor remains stationary.

Using the Controls and Instruments

Familiarizing yourself with the John Deere 3720's controls and instruments is essential for efficient and safe operation. The steering wheel controls the direction of the tractor, providing responsive handling. The throttle controls the engine speed, allowing you to adjust power output for various tasks. The transmission levers control the tractor's speed and direction, typically with multiple forward and reverse gears. The hydraulic levers control implements such as loaders, mowers, and tillers, providing precise control over attachments. Understanding the purpose and function of each control will help you operate the tractor smoothly and effectively. The instrument panel provides vital information about the tractor's operating condition. The tachometer displays the engine speed in revolutions per minute (RPM), helping you maintain the optimal operating range. The temperature gauge indicates the engine's coolant temperature, allowing you to monitor for overheating. The fuel gauge shows the amount of fuel remaining in the tank, preventing unexpected fuel shortages. The oil pressure gauge indicates the engine's oil pressure, alerting you to potential lubrication problems. Understanding these gauges will help you monitor your tractor to minimize risk of damage to engine components. Regularly checking these gauges can help you detect potential issues early and prevent costly repairs.

Operating in Various Conditions

The John Deere 3720 is designed to operate in a variety of conditions, but adjusting your techniques to suit the environment is crucial. When operating on slopes, always drive straight up or down the slope, avoiding traversing across steep inclines to prevent rollovers. Reduce speed and be extra cautious when operating on wet or slippery surfaces, as traction may be reduced, increasing the risk of skidding. When working in dusty conditions, ensure the air filter is clean to prevent engine damage and consider wearing a dust mask for your own health. Always be mindful of overhead obstacles, such as power lines and tree branches, especially when operating with attachments like loaders or mowers. When operating in cold weather, allow the engine to warm up thoroughly before putting it under load, as cold oil can cause excessive wear. Use appropriate cold-weather engine oil to ensure proper lubrication at low temperatures. In hot weather, monitor the engine temperature closely and avoid prolonged idling to prevent overheating. Clean the radiator fins regularly to ensure adequate airflow and consider operating during cooler parts of the day to reduce heat stress on both the tractor and the operator. Adapting your operating techniques to suit the specific conditions will ensure a safe, efficient, and productive operation.

Essential Maintenance

Scheduled Maintenance Intervals

Maintaining your John Deere 3720 compact utility tractor requires adherence to a strict schedule of inspections, lubrications, and replacements. Consulting your operator's manual is paramount, as it contains the most accurate and up-to-date maintenance intervals specific to your model and serial number. These intervals are typically expressed in operating hours (e.g., every 50 hours, 250 hours, 500 hours), but calendar time (monthly, annually) is also important to consider, especially for components subject to degradation over time, regardless of usage. Remember that preventative maintenance is significantly more cost-effective than reactive repairs that result from neglect. Keeping a detailed maintenance log is highly recommended to track completed tasks and anticipate upcoming service requirements.

Ignoring scheduled maintenance intervals can lead to a cascade of problems, from decreased performance and fuel efficiency to catastrophic engine or transmission failure. Proper lubrication, for instance, is critical for reducing friction and wear within moving parts, extending their lifespan and preventing costly replacements. Regular filter changes, such as air filters and fuel filters, ensure that contaminants don't enter sensitive systems, which could cause damage over time. Furthermore, neglecting regular inspections can result in small problems becoming larger and more expensive ones. Regularly checking the fluids can catch a potential problem early on.

Engine Oil and Filter Replacement

Replacing the engine oil and filter is arguably the single most crucial maintenance task for the John Deere 3720. Dirty engine oil loses its lubricating properties and becomes abrasive, increasing wear on engine components such as the pistons, cylinders, crankshaft, and bearings. Regularly replacing the oil and filter removes these contaminants and ensures the engine receives clean, properly lubricated oil. Consult your operator's manual for the recommended oil type (API classification and viscosity grade) and filter specification. Using the correct oil is critical for optimal engine performance and longevity.

Before beginning the oil change, ensure the engine is warm (but not hot) to facilitate better oil flow. Position a drain pan underneath the oil drain plug and carefully remove the plug using the correct wrench size. Allow the oil to drain completely, which may take 15-30 minutes. While the oil is draining, remove the old oil filter using an oil filter wrench and lightly lubricate the rubber gasket of the new filter with fresh engine oil. Spin the new filter onto the engine by hand until the gasket contacts the engine block, then tighten it an additional half to three-quarters of a turn, following the filter manufacturer's instructions. Reinstall the drain plug with a new crush washer (if applicable) and torque it to the specification in your manual. Fill the engine with the specified amount of new oil, using a funnel to prevent spills, and check the oil level with the dipstick. Start the engine and let it run for a few minutes, checking for leaks around the drain plug and oil filter. Finally, recheck the oil level and add more oil if necessary to reach the "full" mark on the dipstick.

Fuel System Maintenance

The fuel system is the lifeline of your John Deere 3720, delivering the necessary fuel to power the engine. Maintaining the fuel system ensures optimal performance, fuel efficiency, and reduces the risk of engine damage. Key maintenance tasks include replacing the fuel filter(s), inspecting fuel lines for leaks or damage, and draining water and sediment from the fuel tank. Contaminated fuel can clog injectors, reduce engine power, and even cause permanent damage.

Fuel filters remove impurities from the fuel before it reaches the engine. Regularly replacing the fuel filter (following the recommended interval in your operator's manual) prevents these impurities from clogging the fuel injectors and causing performance issues. To replace the fuel filter, first, shut off the fuel supply to prevent fuel spillage. Then, carefully disconnect the fuel lines from the old filter and remove the filter. Install the new fuel filter, ensuring it is properly oriented and securely connected to the fuel lines. Bleed the fuel system to remove any air bubbles that may have entered during the filter replacement process. Consult your operator’s manual for the precise location and bleeding procedure for your specific model.

It’s also wise to use a fuel stabilizer, especially if the tractor is stored for extended periods. Fuel stabilizers prevent the formation of gum and varnish deposits in the fuel system, which can cause starting problems and reduced performance. Adding a fuel stabilizer to the fuel tank before storage can help keep the fuel system clean and prevent these issues. Additionally, regularly inspect the fuel tank for water or sediment buildup. Water in the fuel can cause corrosion and performance problems. Drain the fuel tank periodically to remove any accumulated water and sediment, ensuring a clean fuel supply for your engine.

Cooling System Service

The cooling system is essential for regulating engine temperature and preventing overheating. Overheating can cause severe engine damage, including warped cylinder heads and cracked engine blocks. Regular maintenance of the cooling system includes checking the coolant level, inspecting the radiator and hoses for leaks or damage, flushing the cooling system, and replacing the coolant. The correct coolant mixture protects the engine from freezing in cold weather and prevents corrosion in hot weather.

Regularly check the coolant level in the radiator and coolant reservoir. Low coolant levels can indicate a leak in the system, which should be addressed immediately. Inspect the radiator and hoses for signs of leaks, cracks, or deterioration. Replace any damaged components to prevent coolant loss and overheating. Periodically flush the cooling system to remove scale and deposits that can build up over time, reducing the system's efficiency. Always use the coolant type recommended in your operator's manual. Mixing different types of coolant can cause chemical reactions that damage the cooling system components.

During the cooling system service, pay close attention to the radiator fins. These fins are responsible for dissipating heat, and if they become clogged with debris like dirt, leaves, or insects, the cooling system's efficiency will be significantly reduced. Use a soft brush or compressed air to gently clean the radiator fins. Avoid using high-pressure water, as it can damage the fins and further impede airflow. Cleaning the radiator fins regularly will help ensure that the engine operates at its optimal temperature and prevent overheating, especially during demanding tasks.

Hydraulic System Maintenance

The hydraulic system powers various functions on the John Deere 3720, such as the loader, backhoe, and other implements. Maintaining the hydraulic system ensures smooth and reliable operation of these functions. Key maintenance tasks include checking the hydraulic fluid level, inspecting hydraulic hoses and fittings for leaks or damage, and replacing the hydraulic filter. Contaminated hydraulic fluid can cause damage to hydraulic pumps, valves, and cylinders.

Check the hydraulic fluid level regularly and top off as needed with the recommended hydraulic fluid type specified in your operator's manual. Inspect hydraulic hoses and fittings for signs of leaks, cracks, or abrasion. Replace any damaged components immediately to prevent fluid loss and maintain hydraulic system pressure. Regularly replace the hydraulic filter to remove contaminants from the hydraulic fluid. The hydraulic filter is critical for keeping the fluid clean. Contaminants can cause wear and damage to hydraulic components, leading to costly repairs. Consult your operator's manual for the recommended filter replacement interval and procedure.

When working on the hydraulic system, it's crucial to relieve the hydraulic pressure before disconnecting any lines or fittings. Residual pressure can cause fluid to spray out unexpectedly, potentially causing injury or damage. Consult your operator's manual for the proper procedure to relieve hydraulic pressure in your specific model. Typically, this involves lowering any implements to the ground and cycling the hydraulic controls to release any remaining pressure in the system. Always exercise caution and wear appropriate safety gear, such as gloves and eye protection, when working with hydraulic systems.

Transmission and Drivetrain Service

The transmission and drivetrain transfer power from the engine to the wheels, enabling the tractor to move and perform work. Proper maintenance of the transmission and drivetrain is essential for smooth operation and longevity. Key maintenance tasks include checking the transmission fluid level, inspecting the drivetrain components for wear or damage, and replacing the transmission fluid and filter. Neglecting transmission maintenance can lead to slipping gears, reduced power, and eventual transmission failure.

Check the transmission fluid level regularly and top off as needed with the recommended fluid type specified in your operator's manual. Inspect the drivetrain components, such as the axles, gears, and bearings, for signs of wear, damage, or leaks. Replace any damaged components promptly to prevent further damage and ensure reliable operation. Regularly replace the transmission fluid and filter to remove contaminants and maintain proper lubrication. Clean transmission fluid ensures smooth gear changes and protects internal components from wear and tear. Follow the recommended maintenance intervals in your operator's manual for optimal transmission performance and longevity.

Electrical System Checks

The electrical system powers various functions on the John Deere 3720, including the starting system, lighting, and instrumentation. Maintaining the electrical system ensures reliable operation of these functions. Key maintenance tasks include checking the battery condition, inspecting the wiring and connections for corrosion or damage, and testing the charging system. A faulty electrical system can cause starting problems, dim lights, and inaccurate instrument readings.

Check the battery condition regularly and clean any corrosion from the battery terminals. Ensure the battery is securely mounted and the connections are tight. Inspect the wiring and connections for signs of corrosion, damage, or loose connections. Repair or replace any damaged wiring to prevent electrical shorts and ensure reliable power supply. Test the charging system to ensure the alternator is properly charging the battery. A faulty charging system can lead to a dead battery and starting problems. Periodically check the condition of your fuses and replace any that are blown.

Pay close attention to the lighting system, including headlights, taillights, and turn signals. Ensure all lights are functioning properly and replace any burned-out bulbs promptly. Proper lighting is essential for safety, especially when operating the tractor in low-light conditions. Inspect the light fixtures for any signs of damage or corrosion and clean them as needed to ensure optimal brightness. Proper lighting is especially important when operating around other vehicles or in areas with pedestrian traffic.

Troubleshooting Common Issues

Engine Problems

The engine is the heart of your John Deere 3720, and any issues with it can bring your work to a screeching halt. Before diving into complex diagnostics, start with the basics. Check the fuel level and ensure the fuel filter is clean and free of obstructions. A clogged fuel filter is a surprisingly common cause of engine problems and an easy fix. Inspect the air filter as well; a dirty air filter can starve the engine of oxygen, leading to poor performance and reduced fuel efficiency. Finally, verify that the battery is properly charged and that all electrical connections to the engine are secure and corrosion-free.

If the basic checks don't resolve the issue, move on to more advanced troubleshooting. Listen closely to the engine's sound. Unusual noises like knocking, ticking, or hissing can indicate specific problems. A knocking sound might suggest bearing wear, while a ticking sound could be a valve issue. Check the engine oil level and condition. Low oil levels or contaminated oil can cause significant engine damage. Also, examine the coolant level and look for signs of leaks. Overheating is a serious engine problem and can lead to costly repairs. Using a multimeter, check the voltage at the starter solenoid while attempting to start the engine. A significant voltage drop indicates a potential electrical problem.

If your engine is starting but running rough, consider checking the injectors. Dirty or faulty injectors can cause misfires and poor fuel economy. You may need to consult a qualified mechanic with specialized diagnostic equipment for injector testing. Another potential culprit is the governor. The governor regulates engine speed, and a malfunctioning governor can cause erratic engine behavior. Finally, consider the possibility of compression issues. Low compression in one or more cylinders can result in a loss of power and hard starting. Compression testing is typically performed by a professional with specialized tools.

Hydraulic System Issues

The hydraulic system is crucial for many functions on the John Deere 3720, from lifting implements to steering. When troubleshooting hydraulic problems, begin by visually inspecting the entire system. Look for leaks in hoses, fittings, and cylinders. Hydraulic fluid leaks not only reduce system performance but can also be a safety hazard. Check the hydraulic fluid level in the reservoir and ensure it is within the recommended range. Low fluid levels can cause the pump to cavitate, leading to reduced pressure and performance. Also, inspect the hydraulic filter. A clogged filter can restrict fluid flow and reduce the effectiveness of the entire system.

If you're experiencing weak or slow hydraulic performance, the pump may be the source of the problem. Check the pump's output pressure using a pressure gauge. Consult your service manual for the correct pressure specifications. If the pump is not producing adequate pressure, it may need to be repaired or replaced. Another potential issue is a faulty relief valve. The relief valve protects the hydraulic system from overpressure, and if it's stuck open, it can bleed off pressure and reduce performance. Check the valve for signs of damage or contamination.

Problems with specific hydraulic functions, such as a non-responsive loader or malfunctioning three-point hitch, often point to issues with the control valves or cylinders associated with those functions. Inspect the control valve linkages for proper movement and adjustment. A misadjusted linkage can prevent the valve from fully opening or closing. Check the cylinders for leaks or damage to the seals. Leaky cylinder seals can cause slow or incomplete movement. Also, examine the hoses and fittings associated with the affected function. Kinked or damaged hoses can restrict fluid flow, while loose fittings can cause pressure loss.

Electrical System Malfunctions

Electrical issues can manifest in various ways, from a non-starting engine to malfunctioning lights or instruments. Start by checking the battery terminals for corrosion and ensuring they are securely connected. Clean any corrosion with a wire brush and apply a dielectric grease to prevent future corrosion. Inspect the battery cables for damage or fraying. Damaged cables can restrict current flow and cause starting problems. Also, check the battery voltage with a multimeter. A fully charged battery should read around 12.6 volts. If the voltage is significantly lower, the battery may need to be charged or replaced.

Fuses and circuit breakers are designed to protect the electrical system from overloads. Check all fuses and circuit breakers for continuity. Replace any blown fuses with fuses of the same amperage rating. Repeatedly blown fuses indicate a short circuit that needs to be investigated further. If a circuit breaker is tripping repeatedly, it may be overloaded or faulty. Investigate the circuit for any potential problems, such as damaged wiring or faulty components. Also, check the ground connections throughout the tractor. Poor ground connections can cause a variety of electrical problems.

Many electrical components, such as lights and gauges, have their own dedicated wiring harnesses. Inspect these harnesses for damage, such as cuts, abrasions, or loose connections. Use a multimeter to check for voltage at the component's terminals. If there is no voltage, trace the wiring back to the power source, checking for any breaks or short circuits along the way. If you suspect a faulty switch or relay, test it with a multimeter to verify that it is functioning correctly. Faulty switches and relays can prevent power from reaching the intended component.

Transmission Problems

The transmission is responsible for transferring power from the engine to the wheels, and any problems with it can severely impact the tractor's usability. Before assuming a major transmission issue, check the transmission fluid level and condition. Low fluid levels or contaminated fluid can cause slipping, grinding, or other performance problems. Consult your service manual for the correct fluid type and level. If the fluid is milky or discolored, it may be contaminated with water or other debris. In this case, the fluid should be drained and replaced. Also, inspect the transmission filter. A clogged filter can restrict fluid flow and reduce transmission performance.

If you're experiencing slipping or grinding gears, the clutch may be worn or misadjusted. Check the clutch linkage for proper movement and adjustment. A misadjusted linkage can prevent the clutch from fully engaging or disengaging. If the clutch is worn, it may need to be replaced. Another potential issue is a worn or damaged synchronizer. Synchronizers help to mesh the gears smoothly, and if they are worn, shifting gears can be difficult or noisy. Worn synchronizers typically require a transmission overhaul.

Unusual noises coming from the transmission, such as whining or grinding, can indicate internal damage. Whining noises may suggest worn bearings, while grinding noises could indicate damaged gears. These types of problems typically require a transmission overhaul by a qualified technician. Also, check for leaks around the transmission housing. Leaks can indicate damaged seals or gaskets, which can lead to low fluid levels and further damage. Addressing leaks promptly can prevent more serious transmission problems from developing.

Component Repair and Replacement

Engine Components

Servicing the engine components of your John Deere 3720 requires meticulous attention to detail and adherence to safety protocols. Before attempting any repair or replacement, ensure the engine is completely cool and disconnected from the power source. Always consult the engine's specific service manual for torque specifications and approved replacement parts. Improperly installed engine components can lead to reduced performance, increased fuel consumption, and even catastrophic engine failure. When working with fuel lines, be mindful of potential fuel spills and take necessary precautions to prevent fire hazards.

Replacing components such as the fuel filter, air filter, and spark plugs are common maintenance tasks that can significantly improve engine performance. The fuel filter should be replaced according to the manufacturer's recommendations to prevent fuel starvation and maintain optimal fuel delivery. A clean air filter is crucial for preventing dust and debris from entering the engine, which can cause wear and tear on internal components. Regularly inspecting and replacing spark plugs ensures proper ignition and efficient combustion. Using the correct type and gap of spark plugs is vital for optimal engine operation.

For more complex repairs, such as replacing the water pump, thermostat, or cylinder head, it's often recommended to consult a qualified mechanic. These repairs require specialized tools and knowledge to ensure proper installation and sealing. Incorrectly installed water pumps can lead to overheating, while a malfunctioning thermostat can cause temperature fluctuations that damage the engine. When replacing the cylinder head, it's essential to follow the manufacturer's torque specifications to prevent leaks and ensure proper sealing of the combustion chamber. Remember to always use new gaskets and seals to ensure a tight and reliable seal.

Hydraulic Components

The hydraulic system is the lifeblood of many John Deere 3720 functions, powering everything from the loader to the steering. When servicing hydraulic components, cleanliness is paramount to prevent contamination of the system. Even small particles of dirt and debris can damage sensitive hydraulic valves and pumps, leading to reduced performance and costly repairs. Before disconnecting any hydraulic lines, relieve the pressure in the system according to the manufacturer's instructions. This prevents accidental sprays of hydraulic fluid, which can be harmful to your skin and eyes.

Common hydraulic repairs include replacing hoses, fittings, and seals. Hydraulic hoses are subject to wear and tear from pressure, heat, and environmental exposure. Regularly inspect hoses for cracks, bulges, and leaks. Replace any damaged hoses immediately to prevent hydraulic fluid loss and potential equipment failure. When replacing fittings, ensure they are compatible with the hydraulic system's pressure rating and thread type. Incorrect fittings can leak or even burst under pressure, causing serious injury. Always use new seals and O-rings when reassembling hydraulic components to ensure a tight and leak-free connection.

More complex hydraulic repairs, such as rebuilding a hydraulic cylinder or replacing a hydraulic pump, require specialized tools and expertise. Hydraulic cylinders can be rebuilt by replacing the seals and wipers to restore their functionality. Hydraulic pumps are precision-engineered components that require careful disassembly, inspection, and reassembly. If you're not comfortable performing these repairs yourself, it's best to consult a qualified hydraulic technician. They have the knowledge and equipment to properly diagnose and repair hydraulic system problems.

Electrical Components

The electrical system of the John Deere 3720 is essential for starting, operating, and controlling various functions. When working on electrical components, always disconnect the battery to prevent accidental shorts and electrical shocks. Use a multimeter to diagnose electrical problems, such as shorts, opens, and voltage drops. Understanding basic electrical principles, such as Ohm's Law, is helpful for troubleshooting electrical issues. Always refer to the wiring diagram for the specific model year to ensure proper connections.

Replacing components such as the battery, alternator, and starter are common electrical repairs. Batteries should be replaced every few years, depending on usage and environmental conditions. Alternators should be tested regularly to ensure they are charging the battery properly. Starters should be inspected for wear and tear on the brushes and solenoids. When replacing electrical components, ensure they are compatible with the tractor's voltage and amperage requirements. Using the wrong components can damage the electrical system and even create a fire hazard.

More complex electrical repairs, such as troubleshooting wiring harnesses or replacing electronic control units (ECUs), require specialized tools and knowledge. Wiring harnesses can be inspected for damaged wires, corroded connections, and loose terminals. ECUs are complex electronic devices that control various engine and transmission functions. If you suspect an ECU problem, it's best to consult a qualified technician who has the diagnostic equipment to properly diagnose and repair the problem. Incorrectly diagnosing and repairing electrical problems can be dangerous and expensive.

Transmission Components

The transmission is a critical component of your John Deere 3720, responsible for transferring power from the engine to the wheels. Proper maintenance and timely repairs are essential for ensuring smooth and reliable operation. When servicing the transmission, cleanliness is crucial to prevent contamination of the internal components. Always use clean tools and work in a dust-free environment. Before disassembling the transmission, consult the service manual for detailed instructions and torque specifications.

Common transmission repairs include changing the oil and filter, adjusting the shift linkage, and replacing worn clutches or gears. The transmission oil and filter should be changed according to the manufacturer's recommendations to remove contaminants and maintain proper lubrication. Adjusting the shift linkage ensures smooth and accurate gear changes. Worn clutches or gears can cause slipping, grinding, and difficulty shifting. When replacing these components, use only high-quality replacement parts that meet the manufacturer's specifications. Always inspect the transmission for signs of leaks, such as oil drips or wet spots. Leaks can indicate damaged seals or gaskets, which should be replaced promptly.

More complex transmission repairs, such as rebuilding the transmission or replacing the differential, require specialized tools and expertise. These repairs involve disassembling the transmission into its individual components, inspecting them for wear and tear, and replacing any damaged parts. Rebuilding a transmission is a complex and time-consuming process, but it can save you money compared to replacing the entire transmission. If you're not comfortable performing these repairs yourself, it's best to consult a qualified transmission technician. They have the knowledge and equipment to properly diagnose and repair transmission problems. Always follow the manufacturer's instructions and torque specifications when reassembling the transmission.

Attachments and Implements

Compatible Attachments

The John Deere 3720 is a versatile machine capable of handling a wide variety of attachments and implements, greatly expanding its utility for various tasks. Understanding which attachments are compatible and how to properly connect and operate them is crucial for safe and efficient operation. Always consult the specific attachment's operator's manual for detailed instructions and safety precautions. This manual provides general guidance; the attachment manual is the ultimate authority on its use.

Commonly used attachments for the John Deere 3720 include front-end loaders, backhoes, rotary cutters (brush hogs), tillers, box blades, landscape rakes, snow blowers, and mowers. The choice of attachment will depend on the specific tasks you intend to perform. Before purchasing any attachment, verify its compatibility with your tractor's horsepower, hydraulic system, and hitch configuration. Using an incompatible attachment can damage the tractor, the attachment, or both and pose a serious safety risk to the operator and bystanders.

When selecting attachments, consider the weight capacity of the tractor's loader arms (if applicable) and the three-point hitch. Exceeding these limits can lead to instability, component failure, and potential injury. Always refer to the tractor's specifications in this manual and the attachment's manual to ensure that the weight is within safe operating ranges. Also, check the tractor's hydraulic capacity to ensure it can adequately power hydraulic attachments. This is especially critical for attachments like front-end loaders and backhoes.

Installation and Operation

Before installing any attachment, ensure that the tractor is parked on a level surface, the engine is shut off, and the parking brake is engaged. These steps are vital for preventing accidental movement during the installation process. Inspect the attachment and the tractor's connection points for any damage or wear. Damaged components should be repaired or replaced before proceeding with the installation. Never attempt to install an attachment with damaged or worn parts.

The installation procedure will vary depending on the type of attachment. Front-end loaders typically require mounting brackets to be attached to the tractor's frame and the loader arms to be connected to the hydraulic system. Three-point hitch attachments require aligning the attachment's lift arms with the tractor's lift arms and securing them with pins. Pay close attention to the locking mechanisms on the pins to prevent accidental detachment during operation. Once the attachment is connected, double-check all connections for security and proper engagement.

When operating an attachment, follow the manufacturer's instructions carefully. Start slowly and gradually increase speed as you become familiar with the attachment's operation. Be aware of the attachment's limitations and avoid exceeding its rated capacity. Always maintain a safe distance from obstacles and bystanders. Regularly inspect the attachment for wear and tear and perform any necessary maintenance, such as lubricating moving parts and tightening loose bolts. Remember, proper maintenance is key to extending the life of your attachments and ensuring safe operation.

For hydraulic attachments, monitor the hydraulic fluid level and pressure. Low fluid levels can cause the attachment to operate sluggishly or not at all. Excessive pressure can damage the hydraulic system. Follow the maintenance schedule in this manual for hydraulic system servicing. Additionally, ensure all safety guards and shields are in place and properly functioning. These guards are designed to protect you from moving parts and should never be removed or bypassed. Always prioritize safety when operating any attachment.

Storage and Winterization

Preparing Your Tractor for Storage

Properly preparing your John Deere 3720 for storage, especially during the off-season, is crucial for ensuring its longevity and optimal performance when you're ready to put it back to work. Start by thoroughly cleaning the tractor. Remove all dirt, mud, and debris from the body, engine compartment, and undercarriage. A clean tractor is less susceptible to rust and corrosion, which can significantly impact its lifespan. Taking this time to inspect for any existing damage like chipped paint or loose components will allow you to address them before storage begins, preventing further deterioration over time.

Next, address the fluids within your tractor. Change the engine oil and filter, as used oil contains acids and contaminants that can corrode internal engine parts while sitting idle. Similarly, replace the fuel filter and fill the fuel tank completely to minimize condensation buildup, which can lead to rust and fuel system issues. Consider adding a fuel stabilizer to prevent fuel degradation, especially if storing for an extended period. Check and top off all other fluid levels, including coolant, hydraulic fluid, and transmission fluid, to ensure proper lubrication and prevent seals from drying out.

Finally, disconnect the battery. Batteries can slowly discharge over time, and leaving them connected can lead to sulfation and a significantly reduced lifespan. Clean the battery terminals with a wire brush to remove any corrosion and then store the battery in a cool, dry place. If possible, connect the battery to a trickle charger or battery maintainer to keep it fully charged throughout the storage period. This proactive measure will help prolong the battery's life and ensure that your tractor is ready to start when you need it.

Winterization Procedures

Winterization is a critical aspect of preparing your John Deere 3720 for extended storage in cold climates. If temperatures are expected to drop below freezing, draining the cooling system and refilling with the proper concentration of antifreeze is essential to prevent damage to the engine block and radiator. Refer to your tractor's operator's manual for the recommended antifreeze-to-water ratio for your specific climate. Ensure the coolant is properly mixed before adding it to the cooling system to maintain optimal freeze protection. Remember, failing to protect your cooling system against freezing temperatures can result in costly repairs.

Furthermore, consider the tires. Over time, tires can lose pressure, especially in cold weather. This can lead to flat spots and premature wear. Inflate the tires to the recommended pressure listed in your operator's manual before storage. If possible, elevate the tractor to reduce the weight on the tires or place it on wooden blocks. Doing this can help prevent tire deformation during extended storage. Examine the tire sidewalls for cracks or damage, which may require replacement before the next season.

Finally, protect the tractor from the elements. Storing the tractor indoors is ideal, but if that's not possible, cover it with a waterproof and breathable tarp to shield it from snow, rain, and sun. This will help prevent rust, fading, and other weather-related damage. Ensure that the tarp is securely fastened to prevent it from blowing away in high winds. Periodically check the tractor and tarp during storage to ensure everything remains in good condition. By following these winterization procedures, you can rest assured that your John Deere 3720 will be ready to tackle the next season with minimal downtime and expense.

Written by John Deere Jr
Senior Editor & Specialist