We recently had a JLG E300 in the workshop for a slew gear replacement, and we thought we’d share a quick overview of how the job went down. These kinds of repairs demand a precise, step-by-step approach to ensure the machine gets back to full working condition safely and efficiently.
The first step in any major repair job is isolating the machine’s internal systems. On the JLG E300, we began by carefully disconnecting all electrical wiring and hydraulic hoses that run through the center of the chassis. These components connect the base to the boom and control functions, so it’s crucial to remove them systematically and label where necessary. Failing to properly isolate the hydraulic system or electrical network can cause complications during reassembly or even lead to damage. For this reason, we ensure all lines are depressurized, all power is off, and every connector is safely pulled and inspected.
With the wiring out of the way, the next step was removing the ground control box. This panel contains multiple electrical connections that govern ground-level operations. We disconnected all plugs, connectors, and wiring looms attached to the control box and marked each one to make reinstallation efficient. This step ensures we have full access to the machine’s frame without risking electrical damage. It’s also the ideal time to inspect wiring condition, look for corrosion, and plan for any rewiring if necessary.
Next up was the counterweight removal, which allows access to the slew ring and gear components underneath. After unbolting the counterweight, we inserted lifting eye bolts into the designated threaded holes on top of the weight. This let us securely attach lifting slings and use a forklift to remove it safely from the rear of the machine. Proper rigging is crucial here—not only for safety but to prevent stress damage to the frame or surrounding components. The counterweight on the JLG E300 is substantial, so balancing it during lift is a key part of the process.
With the rear end opened up, we shifted focus to the boom assembly. We used a telehandler with a jib hook attachment to secure the boom in place. Then, we undid all 15 slew bolts that fasten the lifting pack to the chassis. Once the bolts were removed, the boom assembly was lifted off and set aside with proper support. Removing the boom not only provides clear access to the slew motor and gear, but it also allows us to inspect the base and turning components for wear. This is a great opportunity to do a full 360-degree inspection of structural integrity and connection points.
Now we were ready to address the root of the issue. We stripped down the slew motor and worm gear assembly, which revealed a damaged brass turning gear—the likely cause of sluggish rotation and grinding noises during boom operation. We removed the damaged gear and replaced it with a new OEM part. The worm gear was also checked for wear and swapped out to ensure smooth meshing and long-term reliability. Before reinstallation, the motor housing was cleaned, and the gears were greased with high-quality gear lubricant to ensure optimal performance.
With the new components installed, we began reassembling the machine in the exact reverse order. This included reinstalling the boom assembly, control box, counterweight, and reconnecting all wiring and hydraulic lines. All the slew bolt was torqued to JLG’s manufacturer specifications using a calibrated torque wrench. This ensures load integrity and safe operation once the machine is back in use. We also performed a full function test to confirm everything operated smoothly, including the slew rotation, lift function, and control system feedback.
After testing, the JLG E300 was fully functional and ready to return to service. The new slew gear eliminated all previous binding issues, and the boom now rotates smoothly under load. These kinds of repairs not only restore performance but also extend the operational life of the machine.
