A properly functioning transmission belt is the lifeblood of your John Deere L120 riding lawn mower, transferring power from the engine to the wheels and enabling smooth movement across your lawn. Over time, this vital component can wear out, leading to tell-tale signs like slipping, a noticeable loss of power, or even complete immobility. Ignoring these symptoms can lead to more significant damage and costly repairs down the line. Fortunately, replacing the transmission belt on your L120 is a manageable DIY project for anyone with a bit of mechanical aptitude and the right tools. This comprehensive guide will walk you through each step, ensuring you can restore your mower’s performance safely and efficiently, saving you time and money on professional service.
Essential preparations and safety first
Before you even think about touching a wrench, proper preparation and unwavering attention to safety are paramount. Working underneath a lawn mower can be hazardous if precautions aren’t taken. Begin by parking your John Deere L120 on a flat, level surface. Engage the parking brake, disengage the Power Take-Off (PTO) lever, and most importantly, remove the ignition key to prevent accidental starting. For an extra layer of safety, disconnect the spark plug wire to ensure the engine cannot crank. Wearing heavy-duty work gloves and safety glasses is also highly recommended to protect against cuts, scrapes, and debris.
Gathering all necessary tools beforehand will streamline the process and prevent interruptions. Here’s a list of what you’ll typically need:
| Tool/Item | Purpose |
|---|---|
| New transmission belt | The replacement part, ensure it’s specific for John Deere L120 |
| Socket wrench set | For various bolts and nuts (metric and/or standard) |
| Open-end wrenches | For holding nuts while tightening/loosening bolts |
| Flat-head screwdriver | Prying, holding components |
| Pry bar (small) | Assisting with belt tension or stubborn components |
| Floor jack and jack stands | Safely lifting and supporting the mower |
| Work light | Illuminating the work area underneath the mower |
| Digital camera/smartphone | Taking pictures of belt routing for reference |
Once you have your tools and have completed the safety checks, carefully use the floor jack to raise the front of the mower, then securely place jack stands under the frame to support it. Never rely solely on a jack. Ensure the mower is stable before proceeding underneath.
Removing the old transmission belt
With the mower safely elevated and secured, you can now access the underside where the transmission belt is located. The belt typically runs from the engine pulley (near the front of the mower) to the transmission pulley (towards the rear) and involves several idler pulleys and a tensioning system. It’s highly advisable to take several clear photos of the existing belt routing from different angles before you start removing anything. This visual reference will be invaluable during the reinstallation process.
The first step in removing the old belt is to relieve the tension. The John Deere L120 usually employs a spring-loaded idler pulley system that maintains tension on the belt. Locate the idler pulley that has a spring attached to it. You will likely need to use a pry bar or a long screwdriver to gently push this idler pulley inward, compressing the spring and slackening the belt. In some cases, there might be a bolt or pin that can be temporarily removed to release tension. Once the tension is relieved, carefully slip the old belt off the various pulleys. Start with the easiest pulleys to access, such as the idler pulleys, and then work your way to the engine and transmission pulleys, which might be more challenging due to their tight fit or surrounding components.
Pay close attention to any guards or brackets that might need to be temporarily removed to gain better access to the belt path. These are usually held in place by small bolts or clips. Keep track of any hardware you remove, perhaps by placing them in a small container, to ensure they can be reinstalled correctly.
Installing the new transmission belt
Once the old belt is completely removed, it’s a good practice to compare it side-by-side with the new belt. Ensure they are the same length, width, and profile. A wrong size belt will not function correctly and could lead to premature failure or damage to your mower’s drivetrain. With the new belt confirmed, you can begin the installation process, essentially reversing the steps you took for removal, but with the added benefit of your reference photos.
Start by routing the new belt around the most difficult-to-reach pulleys first. Often, this means starting with the transmission pulley at the rear and then working forward towards the engine pulley. Carefully follow the path you documented with your photos, ensuring the belt sits correctly within the grooves of each pulley. It’s crucial that the belt is not twisted or pinched anywhere along its path. Work your way around the idler pulleys, making sure the belt is guided smoothly. If you removed any guards or brackets, ensure the belt is routed correctly around or through them before reattaching them.
Once the belt is positioned on all pulleys, you will need to re-engage the tensioning system. Carefully apply pressure to the tensioner pulley (the one with the spring) using your pry bar or screwdriver, just enough to slip the final section of the belt onto the last pulley (often the engine pulley). Ensure the belt is fully seated in all pulley grooves. Once seated, slowly release the tensioner, allowing the spring to pull the belt taut. The belt should feel firm, but not excessively tight, and have a slight amount of play when pressed.
Final checks and testing
With the new transmission belt installed and properly tensioned, it’s time for the critical final checks. Double-check every pulley to ensure the belt is perfectly seated in its groove and that there are no twists or kinks in the belt’s path. Inspect all the hardware you might have removed, ensuring it is securely fastened back in place. Make sure any guards or shields are correctly reinstalled to prevent debris from interfering with the belt’s operation.
Before lowering the mower, give the wheels a manual spin to observe the belt and pulleys in motion. Look for any binding, wobbling, or unusual resistance. Once satisfied, carefully remove the jack stands and lower the mower to the ground using the floor jack. Reconnect the spark plug wire that you disconnected earlier for safety.
Now, it’s time for a test run. Start the John Deere L120 and engage the transmission at a low speed in a safe, open area. Listen for any unusual noises like squealing, grinding, or thumping. Gradually increase your speed and test both forward and reverse gears. The mower should move smoothly, without hesitation or slipping. If you notice any issues, immediately turn off the mower, disconnect the spark plug, and re-inspect the belt routing and tension. A properly installed belt will provide quiet, efficient power transfer, restoring your L120 to its peak performance.
Replacing the transmission belt on your John Deere L120 might seem like a daunting task, but by following these detailed steps, you can confidently tackle this essential maintenance. We’ve covered everything from the crucial preparatory steps and safety measures to the meticulous process of removing the worn belt, installing its new counterpart, and finally, performing thorough checks and a test run. Remember, patience, attention to detail, and proper tool usage are your best allies throughout this repair. Regularly inspecting your mower’s belts for wear and tear can prevent unexpected breakdowns and extend the life of your valuable equipment. By taking the DIY route, you not only save on service costs but also gain a deeper understanding of your machine, ensuring your John Deere L120 remains a reliable workhorse for many seasons to come.
Image by: TOPOS Landscape Architects