Hydraulic Filter Suction Screens – Everything You Wanted to Know

Lately on the forums we have seen a few inquires from folks regarding where they might find their Kubota B or L series hydraulic suction filter. We are happy to hear that people are thinking to check this filter because it can often be hard to locate or just overlooked. Forgetting to check this filter is a definite mistake because it serves an important role and one that we will share with you today.

Role of the Hydraulic Suction Screen
The suction filter is housed internally within the transmission body and it filters and cleans the hydraulic oil of debris, metal flashing, filing from the gears, dirt, rust and other junk. The filter medium is a mesh stainless steel screening and a lot of oil passes over it every minute.

The suction filter medium is a mesh stainless steel screen.

The suction filter medium is a mesh stainless steel screen.

Typical hydraulic pump output on a Kubota is anywhere from 5-6 gallons per minute. Running your tractor for an hour passes more than 360 gallons of oil through this filter! By the time it is ready for cleaning or replacement, it would have filtered more than 100,000 gallons of your Kubota’s hydraulic oil.

Not overly complicated or big but, serves an important role.

Not overly complicated or big but, serves an important role.

Which Kubota Models are Equipped?
All first generation Kubota B and L series models are equipped with hydraulic suction screens. That includes, L175, L185, L235, L245, B5100, B6100, B7100 and so on – primarily tractors built by Kubota in the 1970s and early 1980s.

Wait, what is that you say? You have a newer Kubota so now you can stop reading this article and get back to watching Discovery channel? Well, the reason Kubota stopped using an internal style suction filter has to do with…

Remembering to Service the Filter
Do not be mistaken – it is not hard to get to the filter, inspect and replace or clean it. The trouble with servicing the suction filters is that very few people remember to do it, or know where on their equipment to look. Because these screens are internal they have to be marked by a red dot on the chassis as to their location (more on this in an upcoming article). After 20+ years of rototilling tree shelter belts those red dabs or fender decals indicating filter location have long since faded away.

On top of that, after a tractor trades hands to second, third or fourth owners over the years, it becomes easier to see why a lot people just do not know what to look for. [Editor's note from Mr. K: Folks, do yourselves a favor an buy an operator's manual already!]

Canister Style Hydraulic Filters
Because suction screen type filters do such a good job of catching debris, they are prone to clogging up. Kubota recommends inspection and service every 300 hours if your tractor is so equipped. In the later part of the 1980s Kubota switched over to canister style hydraulic filters not because suction filters were bad, but because so many people forgot to check them.

Canister hydraulic filters are found on all HST Kubota B series, all L-1 series like L2050, L2250, L2550, L2650 and even the newer models from the BX lineup.

How do I know if I have a Blocked Filter?
A blocked suction filter is the number one cause of poor hydraulic system performance. All of these symptoms are indications that the hydraulic circuit is restricted:

  • slow hydraulics
  • shuddering on 3-point when lifting
  • jerky loaders going up
  • overheated transmission oil
  • 3-point working at first and then slowly power fades out

Where is my Suction Filter?
Again, if you have an early B or L series Kubota (ie. a tractor not equipped with a spin-on canister filter), then you will find your filter screen on the left-hand side of the tractor’s transmission.

Check on the left hand side of the transmission just behind the foot rest for a cap covering the filter.

Check on the left hand side of the transmission just behind the foot rest for a cap covering the filter.

Look just behind and slightly below the footrest is where you will find a cap covering the filter. The cap will be secured with two bolts. The cover cap may look like a bump or a teardrop depending on your specific model.

A wider shot to give some context for the filter's location.

A wider shot to give some context for the filter's location.

Removing the bolts will reveal the end of the suction filter itself. The end of the filter will look like it has a small stub sticking out of it (see left-side of second picture in article) about ¼” long and the diameter of a pencil. It may look like a shaft at first blush. If you have a B Series Kubota, the hydraulic filter screen is attached to the large nut holding the suction line against the transmission.

Owners of B series models will have to remove this bolt holding the suction line against the transmission.

Owners of B series models will have to remove this bolt holding the suction line against the transmission.

To remove the filter you will have to grab that small stub-end with a pair of pliers and slowly withdraw the filter. Be careful to not twist it as you pull it out because it is essentially a tube of fine screen.

I’m Having Trouble. Any Other Ideas?
If you are having trouble finding covering cap and the filter screen underneath, find the area on the right hand side of the transmission where the hydraulic suction line enters the transmission. The suction line is the larger of the two lines hooked up to the hydraulic pump. The suction screen and cap will be located exactly opposite this point on the left hand side of the transmission!

Locate the suction line into the hydraulic pump on the right hand side - the hydraulic screen will be opposite this location on the left-hand side of the transmission.

Locate the suction line into the hydraulic pump on the right hand side - the hydraulic screen will be opposite this location on the left-hand side of the transmission.

Servicing the Filter
Before undertaking servicing of the screen be sure you drain the transmission oil first! If not you will soon find out what 9 to 15 gallons of hydraulic oil looks like on the floor of your shop or garage. I know what it looks like and it is not a pretty sight.

With the screen in hand, simply wash it out with diesel fuel or varsol. Once clean inspect the filter mesh for any holes, perforation, rust or tears. Compare your filter screen to the ones you seen in this article. If the filter looks out of shape, replace it rather than trying to work it back into a tube shape. It is out of shape from all of oil, debris, crud and scrum being pulled through it hour after hour.

When your B or L Series was new, Kubota placed an important service reminder on the left hand rear fender showing the service intervals and location of this filter. Kubota has warned us about “various troubles” if we neglect this service! You have been warned.

Close-up of the filter service decal Kubota affixed to early B and L series tractors equipped with screen filters.

Close-up of the filter service decal Kubota affixed to early B and L series tractors equipped with screen filters.

Once clean and inspected, reinstall the filter and refill the transmission with fresh new oil. If you have not seen it already, watch our YouTube video on types of hydraulic oil to use.

There you have it – everything you have ever wanted to know about hydraulic suction filters. Now you can get back to Discovery channel.

Service Department Vic

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