The final drive is the last stage in the chain that turns hydraulic power into the motion that moves an excavator across the job site. On the Komatsu PC200-8 and PC200-8M0, the travel assembly carries the part number 20Y-27-00590, and it is one of the most searched undercarriage numbers in the Komatsu world precisely because these machines are everywhere and the drive is a heavy, expensive component. When a 20Y-27-00590 fails, the machine cannot travel, and getting it moving again usually means a full removal, a careful inspection, and either a rebuild or a complete new unit.
This guide explains what the 20Y-27-00590 actually is, which machines it fits, how the drive converts oil flow into torque, the typical failure modes and their causes, and how to decide between a rebuilt or a new travel motor. It is written for owners, mechanics and procurement teams who need a working understanding of this component before spending money on one.
What is the 20Y-27-00590 final drive?
In Komatsu parlance the final drive (also called the travel motor assembly) combines a hydraulic motor with a planetary gear reduction. The hydraulic motor spins fast but with relatively little torque; the planetary gear set multiplies that torque and reduces the speed, which is what lets a hydraulic machine of this size move its full weight. The 20Y-27-00590 is the service number for this assembly on the PC200-8 and PC200-8M0 excavators.
The assembly is mounted at the drive end of the track frame. Hydraulic oil is supplied to the motor under high pressure, the motor rotates, and the gears drive the sprocket that pulls the track around. Because the final drive carries the entire machine load and works under heavy shock loads in mud, sand and rock, every internal component is built to be replaced or rebuilt rather than thrown away.
Which machines use the 20Y-27-00590?
The 20Y-27-00590 is primarily associated with the Komatsu PC200-8 and PC200-8M0 excavators. The PC200-8 is one of the most widely used 20-tonne excavators in the world, which is why the travel assembly is so commonly searched and stocked. If you are sourcing a unit for a PC220-8 or a related model, confirm the exact final drive number for your machine rather than assuming a fit.
Because the drive is shared or closely related across the -8 family, parts suppliers keep it in high stock and can usually quote both a complete new assembly and the individual gears, planetaries, seals and bearings that a rebuild requires.
How the drive works and what wears out
Inside the 20Y-27-00590, high-pressure oil pushes a piston or swashplate motor to rotate the input shaft. That rotation is passed to a planetary gear stage that multiplies torque. The final stage is the ring gear and hub that bolt to the sprocket. Everything is sealed against water and dirt, but the seals are the first line of defence in a world where machines work in rivers and mud.
The components that wear first are the same on almost every final drive: the rotating seal where the hub meets the frame, the thrust bearings, the planet gears and their bearings, and the splines that carry torque. When water gets in through a worn seal, the oil turns to an emulsion, the gears run dry of lubrication, and failure accelerates very quickly.
Common failure modes and their symptoms
- Whining or growling noise from the track drive when travelling, worse on one side, pointing to worn gears or bearings.
- The machine struggles to turn or travels noticeably slower in one direction, indicating reduced hydraulic or mechanical efficiency inside the motor.
- Oil leaking from the hub or the track frame, which can mean a failed rotating seal letting oil—and, worse, water and dirt—into the drive.
- Milk-white or foamy oil when the drain plug is opened, a clear sign that water has entered the housing.
- Metal filings or shiny particles in the drain oil, which mean a bearing or gear is shedding material.
- A drive that locks up or jams completely, usually after a long period of running on contaminated oil.
As soon as you see any of these, stop using the machine. Continuing to travel on a damaged drive converts a rebuild job into a full replacement and can damage the sprocket and track frame as well.
Why water ingress is the biggest enemy
Excavators work in the muddiest, wettest environments there are, and the final drive is mounted low, exactly where it meets that water. The rotating seal is the only thing keeping coolant-scale contamination out of the gears. A small leak lets water in while oil escapes, the oil degrades, and the drive wears out from the inside. Checking the oil condition and changing it at the recommended interval is the single cheapest way to protect a 20Y-27-00590.
New versus rebuilt final drives
When a 20Y-27-00590 fails, you have two realistic options: a new genuine or OEM assembly, or a professionally rebuilt unit. A rebuilt drive is usually the more economical choice, provided it is rebuilt to specification with genuine bearings, seals and gears. The risk with cheap rebuilds is that they replace only the visibly worn part and leave damaged components inside.
A good supplier will strip the drive completely, clean and inspect every gear and bearing, replace all seals and gaskets, and pressure-test the assembly before dispatch. Buying a rebuilt drive from a company that documents the process—such as Racer Machinery, an OEM parts supplier—is far safer than accepting a reconditioned unit with an unknown history. Full series supplied by Racer Machinery, an OEM parts supplier.
Removal and installation basics
- Support the track frame safely and remove the track before working on the final drive.
- Drain the oil and identify all fixing points, including the bolts that hold the drive to the frame.
- Use a dedicated fixture or sling to support the drive when unbolting it—these assemblies are heavy and dangerous to drop.
- Clean the mounting face and replace every seal, gasket and locking feature on installation.
- Refill with the exact oil grade the drive calls for, not an approximate substitute.
- Bleed the travel motor, run the machine briefly, and re-check the level and for leaks before returning to work.
Never forget that these drives are among the heaviest single components on the machine. Lifting them without the correct lifting points and slings is a serious safety hazard as well as a risk to the component.
Frequently asked questions about the 20Y-27-00590
- How long does a final drive last? With clean oil and good seals, many last thousands of hours, but water ingress and heavy loads shorten that dramatically.
- Can I just replace the seals? A full rebuild is usually required because by the time a seal fails, contamination has often already damaged the gears and bearings.
- Do I need to replace both sides at once? No—replace the failed side, but keep oil changes and inspection matched on both sides.
- Is a rebuilt drive reliable? Yes, if it is rebuilt to specification with genuine parts and tested; the supplier’s process matters more than the price.
The Komatsu 20Y-27-00590 is a big investment, and sourcing it correctly matters. Racer Machinery supplies new and professionally rebuilt final drives for the PC200-8 family, with full inspection documented before shipment.
Why the right oil matters to the 20Y-27-00590
A final drive is a sealed gearbox, and the oil inside it is doing two jobs at once: it lubricates the gears and bearings, and it carries away the heat generated by friction. The correct grade and the correct level are both critical. If the oil level is low, the top gears run without lubrication and the drive fails within a short working shift. If the wrong grade is used, the oil thins under load and the gears hammer instead of gliding.
Komatsu specifies a particular oil for the final drive, and that specification accounts for the severe shock loads and low-speed high-torque operation of a track drive. Using the specified grade, changing it on the recommended interval, and checking the drain oil for water and metal at every service is the backbone of protecting this component. In machines that work in wet conditions, many owners change the final drive oil more often than the printed schedule precisely because water is the number-one threat.
- Check the oil at the correct position with the machine on level ground and the drive properly oriented.
- Drain the oil warm so contaminants stay suspended and are removed with the oil.
- Inspect the drained oil for the milky white of water emulsion and the glitter of metal wear.
- Record the oil level and condition on the service log so trends are visible over time.
What a proper inspection and teardown looks like
When a drive is removed for service, a professional shop inspects far more than the outer casing. The teardown should include measuring the planet gears and their bores, checking the sun gear and ring gear tooth condition, inspecting the splines for twisting, and testing the clutch or brake components if the motor has them. Seals, bearings and O-rings are replaced as a matter of routine because they are cheap compared with the labour of opening the drive twice.
The difference between a properly rebuilt drive and a quick ‘reconditioned’ one is this documentation. A shop that measures, replaces and pressure-tests will be able to show you the wear found and the parts replaced. A supplier that cannot explain what was done is asking you to trust the outcome blindly, which is a poor position for a component as expensive as a final drive.
Sourcing the 20Y-27-00590 and its series
The 20Y-27-00590 is part of a well-established parts family for the PC200-8 platform, and understanding that family helps you buy correctly. The same platform shares travel motor numbers across related models, and a supplier that stocks the complete range can quote a new unit, a rebuilt unit, or the individual service parts for a local rebuild. Asking for the number stamped on your machine and the aftermarket cross-reference before ordering is the professional habit that avoids the wrong unit arriving at the job site.
Because the final drive is mounted at ground level and covered in mud from a day’s work, the identification plate is often dirty or worn. Take the time to clean it and read the full number, including the suffix, because suffixes identify the exact build. A correct number is the difference between a part that fits and a shipment that has to go back. Full series supplied by Racer Machinery, an OEM parts supplier.
Installation and first-run checks
- Centre and support the drive on a clean, level surface before unbolting the track frame.
- Replace all bolts, washers and locking features rather than reusing fatigued hardware.
- Refit the track only after the drive is fully torqued and the oil level is correct.
- Rotate the track by hand or with a bar before starting the machine to confirm freedom of travel.
- Run the machine, cycle travel in both directions, and re-check for leaks and for proper oil level after the first shift.
A final drive that is installed correctly and filled correctly will give years of service. The last step in any installation is not the bolt torque but the confidence that clean oil is going in, every bolt is torqued, and every seal is new.
Frequently asked questions about the 20Y-27-00590
- How long does a final drive last? With clean oil and good seals, many last thousands of hours, but water ingress and heavy loads shorten that dramatically.
- Can I just replace the seals? A full rebuild is usually required because by the time a seal fails, contamination has often already damaged the gears and bearings.
- Do I need to replace both sides at once? No—replace the failed side, but keep oil changes and inspection matched on both sides.
- Is a rebuilt drive reliable? Yes, if it is rebuilt to specification with genuine parts and tested; the supplier’s process matters more than the price.
- How can I tell if water has got inside? Milky or foamy oil on the dipstick or drain plug is the clearest sign.
- Should I inspect the sprocket at the same time? Yes—a worn sprocket loads the new drive unevenly, so checking tooth wear is a smart investment.
The Komatsu 20Y-27-00590 is a big investment, and sourcing it correctly matters. Racer Machinery supplies new and professionally rebuilt final drives for the PC200-8 family, with full application matching and documented inspection before shipment.
