Excavator Slewing Ring: What It Is and When to Replace It

What does a slewing ring do on an excavator?

The slewing ring does three jobs at once, which is why it is built the way it is.

It carries the weight. The whole upper structure sits on hardened steel raceways inside the ring, with rows of balls or rollers between them. It resists tipping. When the boom is out and loaded, the machine is trying to tip forward, and the ring has to take that bending force, not just the downward weight. And it drives the rotation. One face of the ring is cut into gear teeth, and a swing motor with a planetary gearbox meshes into those teeth to turn the house.

That third job is why a slewing ring is not simply a bearing. It is a bearing and a gear in one piece, and the two wear differently. The raceways wear from load and dirt. The teeth wear from the swing motor pushing against them thousands of times a day, always hardest in the arc the operator uses most, which on a truck-loading job is a narrow 90-degree band that gets punished while the rest of the ring stays fresh.

The excavator components guide places the ring in the machine as a whole, and the undercarriage guide covers what sits below it.

How fast does an excavator swing, and why does size change it?

Swing speed is measured in rotations per minute (rpm), and across the 288 excavators with a published figure it runs from 3.1 rpm on the largest mining machines to 13.8 rpm on a 12 tonne class machine. Bigger machines swing slower, and that is deliberate: the further the mass sits from the centre, the more force the ring and the swing motor have to absorb at the start and end of every turn.

Specifications as per the current Aug 2026 listings. Two practical points come out of that table. First, a slow swing speed on a big machine is normal and is not a fault. Second, if a 20 tonne machine that should turn at around 13 rpm is visibly slower than a similar machine beside it, that is worth investigating before you buy, because a tired swing motor and a worn ring both show up the same way.

Swing circuit pressure, quoted in megapascals (MPa), is the hydraulic pressure the swing motor works at, and on the listed machines it runs from about 16.6 MPa on small excavators to 32.4 MPa on larger ones. It matters here because the harder that circuit works, the harder the teeth are being pushed.

Compare working specifications across the full range of excavators, and read the excavator size classes guide to place a machine in its class before comparing its numbers to anything else.

What are the signs of a worn slewing ring?

A slewing ring rarely fails suddenly. It gives warning for months, and the warnings are easy to feel from the seat:

• A knock at the start and end of every swing. This is backlash, the free play between the gear teeth and the swing pinion. A small amount is normal on any machine. A distinct clunk you can hear over the engine is not.
• Rocking under load. Boom out, bucket loaded, and the house tips or settles slightly. That means the raceways are worn and the upper structure is no longer sitting flat.
• Grinding or a gritty feel through the swing. Usually dirt that has got past the seal, and it is the stage at which greasing still helps.
• Grease coming out black with metal flecks. Grease should come out dirty. Grease that glitters is the ring wearing itself away.
• Uneven wear across the circle. Swing the empty machine slowly through 360 degrees. If it is smooth for three-quarters of the turn and rough in one arc, that is the arc the last operator worked in, and it tells you the machine’s history better than the hour meter does.

That last check is the useful one, because it separates a machine that has done light hours everywhere from one that has done hard hours in one place.

How do you check the slewing ring on a used excavator?

The standard trade check is the tilt test, and it needs nothing but a helper and something to measure with. Park the machine level. Put a dial gauge or a fixed reference mark between the house and the undercarriage at the front. Now raise the machine’s front off the ground on the boom and bucket, and measure how far the house lifts away from the undercarriage.

That gap is the wear in the raceways. Every manufacturer publishes a limit for its own machines, so the number to compare against comes from the dealer or the service manual for that model, not from a general rule. What matters is that you take the measurement, write it down, and ask the dealer what the limit is for that model before money changes hands.

Alongside it, do three things:

1. Swing the full circle twice, once empty and once with the bucket loaded and the boom extended, listening for the change.
2. Look at the seal around the ring. A split or hardened seal means dirt and water have been getting in, whatever the grease looks like.
3. Check the bolts. The ring is bolted to the frame above and below with a large number of high-tensile bolts. Any that are missing, replaced with a mismatched bolt, or showing paint cracked around the head have been moving.

These checks belong in the wider inspection covered in the used excavator buying guide, and the used construction equipment guide sets out the paperwork side. Browse the current excavator models and prices when you are ready to compare against a new machine.

How do you make a slewing ring last?

Almost every early slewing ring failure comes down to grease and dirt, and both are within the owner’s control.

Grease it on schedule and grease it turning. The ring has grease points that feed the raceways, and pumping grease into a stationary ring only fills one spot. The correct method is to grease, swing the house part of a turn, grease again, and repeat until you have been all the way round. On most machines the interval is measured in tens of hours, so it belongs on the daily or weekly card rather than the service visit.

Grease the gear teeth separately. The teeth usually sit in an open or semi-open bath at the bottom of the ring and take a different, heavier grease from the raceways. Check the level; do not assume it is full because the raceway points took grease.

Keep the seal intact. A split seal costs a fraction of the ring it protects. In dusty conditions and through the monsoon, inspect it rather than waiting for a service.

Change the operator’s habit, not just the grease. Slamming the swing from full speed into a stop, and using the swing to push spoil sideways, both load the teeth in exactly the way they are not designed for. Working the machine across a wider arc rather than the same narrow 90 degrees also spreads the wear.

The hydraulic system maintenance guide covers the swing motor side of the same system, and the excavator oil and hydraulic capacities reference gives the quantities for the routine services.

What does slewing ring replacement involve?

Replacement is a workshop job, not a site job. The upper structure has to be lifted clear of the undercarriage with a crane, the old ring unbolted, the mating faces cleaned and checked for flatness, the new ring fitted with its bolts torqued to a specified pattern, and the whole thing reassembled. On a 20 tonne machine that is typically several days off work, and the machine downtime often costs more than the part.

We do not list slewing rings as a catalogue item, so there is no price to quote here; the figure comes from your dealer for your specific model, and it varies a great deal between a genuine ring and an aftermarket one. What is worth knowing before you ask is that the choice between genuine and aftermarket matters more on this part than on most, because the hardness of the raceway is what determines whether you do this job once or twice.

Two things make the difference between a repair that lasts and one that does not. The mating surface has to be genuinely flat, because a ring bolted to a distorted frame is loaded unevenly from the first hour. And the bolts must be new and torqued correctly, in the right sequence; reused bolts are a common shortcut and a common reason a rebuilt swing fails early.

If the machine you are looking at needs one, treat the cost as part of the purchase price and negotiate on that basis. Compare it against a machine that does not need the work: browse the range of excavators and connect with a dealer, or start from the excavator guide hub for the rest of the series.

Prices, specifications and features are indicative, vary by variant, location and date, and should always be confirmed with the official OEM or authorised dealer before any purchase decision. DesiMachines is not liable for decisions taken on the basis of information that may have changed after publication. Specifications are taken from our listings at the time of writing.