A swing drive is a major component on excavators that allows the top portion of the excavator containing the cab and boom to swivel independently from the undercarriage containing the tracks. It is one of the most vital parts on an excavator and without it, an operator would have to back up and adjust the angle of the entire machine to turn, costing time to complete a job. Here’s everything you need to know about your swing drive, how it works, and what to do to keep it running.
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What is a Swing Drive?
A swing drive is an essential part of any excavator, powering the rotation of the upper platform of the cab and boom. Without it, the excavator would be locked into a single direction. The swing drive specifically is what powers the rotation of the top portion of the excavator. It is located withing the rotary joint below the top assembly, and is accessible most commonly from the deck on the top assembly.
What Are the Parts of a Swing Drive?
A swing drive consists of a hydraulic motor, a gear box—which contains planetary gears—and a pinion shaft. Not technically part of the swing drive but just as important is the slew ring or slew gear, which is what rotates the upper and lower portions of the excavator.
How Does a Swing Drive Work?
The motor itself is the powerhouse of the swing drive, controlling the flow of hydraulic fluid and turning that fluid movement into kinetic gear turning. The planetary gears within the gear box in turn convert that high-speed kinetic movement put out by the motor into focused torque, which in turn spins the pinion gear shaft. The spinning of the pinion shaft rotates against the slew ring and twists the upper assembly of the excavator. Without these mechanical processes an operator would have to completely reposition the excavator in order to swing the boom arm to the side.
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How to Troubleshoot a Swing Drive
Like with most mechanical parts on an excavator, regular maintenance and early detection of breakage can prevent most major issues or catch them early enough that they don’t balloon into major repairs. When checking your swing bearing, it’s important to keep an eye and ear out for the following symptoms:
- • Slow or weak motion: This is one of the most common symptoms and often points to a hydraulic issue such as low hydraulic pressure or pressure lost, worn seals, or blocked filters. If the swing of your machine feels sluggish, it’s important to take a look at the hydraulic systems for the issue.
- • Vibrations or jerky movement: uneven or jerky movement often points to air in the hydraulic system or valve issues such as sticking valves, or uneven pressure from the control valve.
- • Unusual noises: If anything on your machine is making strange, squealing, or clanking noises, it’s a major issue, but doubly so if it’s coming from the swing assembly. Grinding or knocking noises usually indicate broken gears within the gear box, damaged bearings, or contamination within the hydraulic oil.
Swing Drive Maintenance
To prevent a small issue from ballooning into a major one, it’s important to adhere to a regular maintenance schedule.
- • Look for obvious leaks of hydraulic fluid from hoses, fittings, and the swing motor assembly. Check for signs of corrosion as they are often indicators of loose fittings and damaged lines.
- • Check fluid levels and condition of said fluid. A low level of hydraulic fluid will cause additional issues if not topped up, and contaminated fluid can cause damage to internal components such as the seals. Check hydraulic fluid and oil for metal shavings, discoloration—such as a milky appearance—and for any strange burnt smells.
- • Check the filters. Clogged filters or filters long overdue for a change affect hydraulic pressure and can lead to unusual movement in the swing mechanisms. If a filter has metal shavings or flakes caught in it, it’s likely an indicator of grinding or improperly fitting gears shearing off metal.
- • Test the hydraulic pressure at specific points in the system. Compare your results at different points to determine where a problem lies. If there’s a difference between hydraulic pump and the swing drive, there’s likely a leak somewhere that will need to be repaired.
- • Inspect the swing control valve located in the top portion of the swing drive. An issue with this valve cascades further down and can cause uneven rotation, a slow response, or having the mechanism only swing to one side.
- • Finally, you should perform an operational test with an unloaded bucket. If the machine passes and you don’t notice any sticking, jerking, or unusual noises, your machine is ready to operate.
