Do You Have To Bleed Hydraulic Lines On A Kubota Tractor? [Why, How & When]

Hydraulic lines are the muscle behind everything your Kubota tractor does, outside of propelling itself backward and forward. So no matter how careful you are, with all the lifting, pulling, and pushing your Kubota is made for, you will get air in the hydraulic lines.

You should occasionally bleed the air out of your hydraulic lines when your Kubota is older. Not only does air have the potential to damage your equipment, which is rare but possible, but it’s also a safety hazard since it can cause hesitation in your lifting, pulling, and pushing capabilities. 

As we mentioned, it’s not likely that a little bit of air in your hydraulic lines will cause any damage to your Kubota tractor since it self-ventilates. But it might cause problems while you are using the tractor’s hydraulic capabilities, especially with hesitation when the air creates gaps in a pressurized system that the self-bleeding process fails to capture.

Kubota’s are Designed to Self-Bleed

In a Kubota tractor and most other modern tractors, the lift cylinders are vertical when the front-end loader is up and horizontal at its lowest point. Therefore, the lines that go into these cylinders are located on the top of the cylinders.

This is by design. As the cylinder compresses, breathing pressure in the hydraulic system, the air is forced up, assisted by the laws of physics, and back into the valves where it is released. 

Also, the seals are designed to release air. While leaving no room for releasing the hydraulic fluid, so it’s a two-pronged design that helps to eliminate air from the hydraulic system just by using the hydraulic system and not by any other unrelated action.

However, no matter how many times someone tells you that modern-day tractors—in this case, Kubota tractors—will self-bleed, nothing in machinery remains perfect over time. 

Seals get gunked up, lines get older and less flexible, cylinders fail to compress, and the working guts of the Kubota simply age. 

When this happens, the air bleeding that was once automatic becomes less so. Unfortunately, this means that if you are a Kubota owner, there will come a time when you may have to bleed the air out of the hydraulic lines. 

Most of the time, this means cycling the cylinders and nothing more. 

But it may be necessary, down the road, to take a more active approach and bleed the lines themselves or simply cycle the cylinders, using physics to aid a Kubota’s ability to bleed the air out of the lines.

What Happens If You Don’t Bleed The Air?

Several things occur when air gets into the hydraulic system. Unfortunately, it doesn’t bleed off automatically or is not physically bled off. Instead, the following occurs.

  • Controls will get a bit squishy
  • Horsepower loss
  • Foaming
  • Loss of hydraulic fluid
  • Cavitation

Cavitation is the erosion of critical hydraulic system parts when the components are starved of hydraulic fluid. Erosion includes pitting on the surface or more severe erosion. Cavitation is uncommon in Kubota tractors, however.

Foaming is another side effect when the air and hydraulic fluid mix. It causes the operation of hydraulic-dependent components to get flaky, hesitant, or sluggish, losing much of the necessary horsepower. 

If any air makes its way back to the reservoir, it will effectively displace the hydraulic fluid that is there, which can cause severe issues in the rest of the system, as there is very little hydraulic fluid to draw from since the air has displaced it. 

This is another rare circumstance in a Kubota tractor but not unheard of, especially in older models, in which this example is a symptom of a much larger problem.

How to Cycle Your Cylinders

You should consider this a form of maintenance—the kind of maintenance that should have a built-in routine. It’s not something that you have to do often, not even as often as you change your oil. 

Cycling the cylinders will effectively bleed out any missed air in the automated, built-in process. So it’s not some convoluted process that requires you to go out and pick up a whole bunch of expensive equipment. 

The older your Kubota gets, the more often you may have to cycle the cylinders. To do this, raise the front-end loader to its maximum height and allow it to remain where it is while you hop back into the seat. 

Run the tractor at low idle and turn the steering wheel as far as it will go to the left and as far as it will go to the right. 

Do so slowly, not quickly. It should bleed all of the air out of the cylinders and any air passing through them. 

You can achieve better and more efficient cycling if you can also jack up the front axle. You will need to place something under it, like a jack stand, to hold it in place while you work the wheel left and right. 

How to Bleed the Hydraulic Lines in Your Kubota

If you need to go this far, it’s a simple matter of having something to collect the hydraulic fluid and someone sitting in the tractor to activate the hydraulics. 

Whoever is using the hydraulics needs to be quick on their feet because you only want to do this until you get a clean stream of hydraulic fluid. 

As soon as that happens, stop using the hydraulic system and reconnect the line. You will only remove one line at a time and work your way from one to the next. You don’t want to disconnect all of your lines because you will have hydraulic fluid spraying everywhere. 

Start from the left side and work your way across. Disconnect your first hydraulic line and use a large, plastic measuring cup to capture the fluid. 

Have someone activate the hydraulic lines while you hold the cup underneath each one. You should get air first, but you want to ensure you have an uninterrupted flow of hydraulic fluid before you shut it off. 

Reconnect the first line and move on to the next one, repeating the process throughout the system, which should be too extensive. 

Replacing the Hydraulic Lines on Your Kubota

Sometimes, it’s not an issue with the tractor failing to clear out the air from the lines, it’s just a matter of defects in the line or lines, and they will need to be replaced. 

Fortunately, replacing the hydraulic lines in a Kubota tractor is not a complex problem as they use simple, snap-on connections, making them easy enough to remove when you need to replace them with a new one. 

If the problem is something going on in the cylinders or throughout the system. It may be time to call it a day and haul the tractor off to a professional tractor mechanic that can effectively diagnose and repair the problem. 

Final Word

Hopefully, you will never need to do anything more than cycle your cylinders from time to time as your Kubota tractor gets older. However, a well-maintained Kubota tractor will rarely experience any issues in the hydraulic system.

These are well-built tractors designed for the long haul. Taking care of it and establishing a preventative maintenance routine goes a long way. 

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