The slew bearing — the large ring gear that lets the upper structure rotate on the base — is one of the hardest-working critical components on any slewing EWP. It carries the entire weight of the boom, platform and load, and it takes the overturning moment every time the machine reaches out to one side. Because it sits between the turntable and the chassis, it also lives out of sight and out of mind until something feels wrong. This guide explains how a slew bearing wears, the tell-tale movements that signal trouble, how the wear is measured and why replacement is a considered job.
Symptoms of a worn slew bearing
Wear in the slew ring tends to show as unwanted movement and noise:
- A knock, clunk or notchy feel as the machine starts and stops slewing, or as the boom is raised and the load shifts across the bearing.
- Visible rock or tilt at the turntable — the upper structure moving relative to the base when the boom is loaded to one side.
- Grinding, rumbling or graunching noises from the slew ring during rotation.
- Slew that has become rough, hesitant or uneven, which can point to worn or damaged gear teeth as well as bearing wear.
- Metal particles or discoloured grease purged from the bearing, a sign of internal wear.
Why slew bearings wear
- The sheer duty they carry — every load and every overturning moment passes through the same raceway and the same teeth.
- Inadequate or contaminated lubrication, which lets the raceway and rolling elements wear and can allow corrosion inside the bearing.
- Bolt tension loss, where slew ring fasteners loosen over time and let the bearing move and pound, accelerating wear and stressing the bolts.
- Working on a slope or with side loads, which increases the moment the bearing must resist.
- Water and grit ingress past worn seals, which turns grease into a grinding paste.
How wear is measured at inspection
Slew bearing wear is not judged by feel alone — it is quantified. The standard field method is a tilt or rock check: with the boom set to load the bearing in a defined way, the inspector measures the movement between the upper structure and the base, typically with a dial gauge, and compares it against the manufacturer's wear limit.
Alongside the movement check, a competent inspector verifies the slew ring bolt tension, inspects the gear teeth for wear and damage, and assesses the condition of the grease and seals. Because the slew bearing is a critical component, it receives close attention during periodic inspections and is examined in depth during the major inspection — the AS 2550.10 check whose interval is 5 years for certain machine classes and 10 years for the rest.
Repair and replacement
A slew bearing is not repaired in the sense of being rebuilt in the field — worn raceways and rolling elements are not serviceable. Where measured wear exceeds the limit, or the teeth or raceway are damaged, the ring is replaced.
- Separate the upper structure from the base, which requires supporting or removing the boom and turntable safely.
- Remove the old slew ring and inspect the mating faces on the turntable and chassis for flatness and damage.
- Fit the correct replacement bearing, orienting any soft spot or filler plug away from the highest-loaded position per the manufacturer's guidance.
- Tension the slew ring bolts to the specified torque in the correct sequence, using new fasteners where required.
- Grease, function test the slew through its full rotation, re-check bolt tension after initial operation and document the work.
Getting the most life from a slew bearing
The two biggest levers are lubrication and bolt tension. Greasing the slew ring on schedule, rotating the bearing so grease reaches the whole raceway, keeps wear and corrosion at bay, and checking slew bolt tension at the intervals set by the manufacturer stops the loosening that lets a bearing pound itself out.
Avoiding unnecessary side loading and keeping the machine level when working extends bearing life too. If a slew develops a knock, rock or grinding noise, treat it as a critical-component fault and have it assessed rather than working through it.
This guide is general information prepared by EWP Australia and is grounded in publicly available Australian Standards and Safe Work Australia material. It is not a substitute for the current published edition of the relevant standard or for site-specific engineering advice. Always work from the current standard and consult a competent person for your specific equipment and application.