Kubota ZD221 No Hydraulic Pressure

[bruiserstone75]

Hello all, long time lurker first time poster.

I have a ZD221 with a little over 900 hours on it I purchased used last year. Was running and performing fine until I replaced a leaking left side axle shaft seal on the outer housing. After replacing the oil seal on the axle shaft, I replaced the hydraulic fluid, changed the filter, and verified it was full on the dipstick. I jacked up the rear of the mower and ran the axles forward and reverse for about a minute a piece. I took it for a test ride and after about 3-4 minutes the mower slowed to a stop. I got it back in the shop and looked for leaks. Finding none, I put it back on the jack and tried the hydraulics. Very slow movement on LH and RH axles, no movement at all in the deck actuator. I flushed the hydraulic fluid from the case and axles, checked and cleaned the strainer and refilled. Still nothing. I checked the shims in the bypass valve and verified two were present. I took apart the repair I did on the axle shaft seal and verified that everything was seated correctly and the brake was set properly. I have noticed quite a bit of foaming/frothing in the fluid when I look in the breather/fill hole while running. I am reasonably sure I am getting it full of fluid, I put in almost 2 gallons when completely empty and it's to the full mark on the dipstick. I'm running hydraulic fluid from Tractor Supply with Kubota UDT listed on the bucket with Wix filter.

I have cleaned the HST and run it on the jacks and have yet to see anything leaking. My best guess is that there's some internal seal that has failed. But before I dug into a major rework project I was hoping that someone had seen something similar and knew of anything else to check.

Any help is greatly appreciated . Thanks all!

 

[Outnumbered]

I know my ZT is not a Kubota but spells out a process to bleed the air out of the pumps when the oil is changed. In my case it was as simple as jacking up the rear and then placing the pump bypass into the towing mode and to move the levers and wheels back and forth. Place it back on the ground, disengage the freewheel/tow selector and off you go. I have to do it every time I change the oil.

 

[lugbolt]

there is no bleeding procedure needed on the ZD transmissions

but

when you pull an axle housing off, or drain it (leaking seal), you'll lose all the oil out of the axle housing. There are two ways to refill it. One, fill it with the fill plug in the axle housing, and/or two fill it in the center case next to the dipstick. If you use #2, the center case fluid will be picked up by the charge pump, which sends it to the hst's. There are two of them, one left one right. The charge pressure bleeds off of the hst's as "drain oil" and is forced into the axle housings. So, if you fill it once in the center case, with a dry or low level in an axle case, the oil you just poured in went partially to the dry axle housing and now your center case oil level is going to be low. It takes quite a few cycles to get the center case filled back up so that it holds the level. And with cheap fluid, it is thicker than super udt2, and takes longer to fill the axle housing. Also, some of the chemicals in the cheap oil can play havoc with brass parts, which is why I don't recommend using it. But to each their own, it's already in there, use what you have. Even with udt2, refilling both axle housings after a fluid change can take 45 min to an hour's worth of cycling (fill to dipstick full level, run engine, shut it off, wait, check, refill, repeat)

If after a few fill, run cycles the oil level levels off, and it still isn't working, pull the suction screen and see what's on it. That will tell you which direction you need to go. If nothing at all on it (no metal), you may be ok. You don't want to see any metal filings on it. If you do, figure on opening it all up to see what's wore out/broken/damaged. If no metal, and you see lots of aeration in the oil, look at your suction tubes and their o-rings/seals. If you get a suction side leak (or low oil level) the suction side of the pump will pick up air and aerate the oil and you will see lots of bubbling. You'll always get some bubbles, especially with the TSC fluid (udt2 has an additive package that helps reduce aeration) because of how the center case is designed. Just not a lot, at least not normally.

does the pto work? Deck lift work? It's hydraulic as well, works off of charge relief pressure (for the most part). if it works, the charge pump is charging and at that point it's going to be either linkage or internal.

 

[bruiserstone75]

Thanks for the super detailed responses.


I was refilling the axle housing via the upper fill plug until fluid ran out.

I pulled the strainer and cleaned it with solvent but didn't see any metal filings.

I am getting lots of foaming in the fluid.

At this point when i push the levers, I get slow movement from the rear axle for about 30 seconds then it stops. The PTO does turn the deck but the deck lift does not move.

I was unaware there was that significant of a difference between the Kubota UDT and other brands, I guess I assumed that Valvoline or Amalie bottled it all to the same spec. When I refill it I will see if I can find the Kubota branded fluid.

I will go take a closer look at the lines and see if they are leaking or drawing air in.

Thanks for the advice!

 

[TheOldHokie]

Thanks for the super detailed responses.


I was refilling the axle housing via the upper fill plug until fluid ran out.

I pulled the strainer and cleaned it with solvent but didn't see any metal filings.

I am getting lots of foaming in the fluid.

At this point when i push the levers, I get slow movement from the rear axle for about 30 seconds then it stops. The PTO does turn the deck but the deck lift does not move.

I was unaware there was that significant of a difference between the Kubota UDT and other brands, I guess I assumed that Valvoline or Amalie bottled it all to the same spec. When I refill it I will see if I can find the Kubota branded fluid.

I will go take a closer look at the lines and see if they are leaking or drawing air in.

Thanks for the advice!

Your problem is not the brand of oil.

Dan

 

[whitetiger]

Thanks for the super detailed responses.


I was refilling the axle housing via the upper fill plug until fluid ran out.

I pulled the strainer and cleaned it with solvent but didn't see any metal filings.

I am getting lots of foaming in the fluid.

At this point when i push the levers, I get slow movement from the rear axle for about 30 seconds then it stops. The PTO does turn the deck but the deck lift does not move.

I was unaware there was that significant of a difference between the Kubota UDT and other brands, I guess I assumed that Valvoline or Amalie bottled it all to the same spec. When I refill it I will see if I can find the Kubota branded fluid.

I will go take a closer look at the lines and see if they are leaking or drawing air in.

Thanks for the advice!

Your problem is you do not have the system full of oil, you can not fill the system with the plugs at the top of the axle housings. You need to tip the seat forward to access your dipstick and a fill port. Fill the reservoir and drive the unit, recheck until it stays full.

When you are mowing, if you notice it whining, jerking while turning or when you start moving, save yourself a lot of money later by changing out the economy oil and refilling it with SUDT 2. We play this little cheap oil game with customers several times a year, year after year. Most ZD hydrostats benefit greatly from the Kubota SUDT 2 oil.

 

[bruiserstone75]

Sorry, should have been more clear on how I refilled the HST. I filled the transmission from the fill port under the seat (changed the filter too). I filled the left and right axle housings via the upper plug. According to the dipstick I'm at the full mark. I put in almost 2 full gallons of fluid in total. I've cranked it up several times to check for leaks and try the hydraulics. The local Kubota dealer thinks it may be hydrolocked. Sounds like the consensus is that there is air in the system somewhere but darn if I can figure out how to get it out.

I had no idea that the Super UDT was that much different than the average hydraulic fluid. I'll happily refill it with that if I can get it back up and going.

i appreciate everyone taking time out to offer advice. Thanks a bunch

 

[TheOldHokie]

Sorry, should have been more clear on how I refilled the HST. I filled the transmission from the fill port under the seat (changed the filter too). I filled the left and right axle housings via the upper plug. According to the dipstick I'm at the full mark. I put in almost 2 full gallons of fluid in total. I've cranked it up several times to check for leaks and try the hydraulics. The local Kubota dealer thinks it may be hydrolocked. Sounds like the consensus is that there is air in the system somewhere but darn if I can figure out how to get it out.

I had no idea that the Super UDT was that much different than the average hydraulic fluid. I'll happily refill it with that if I can get it back up and going.

i appreciate everyone taking time out to offer advice. Thanks a bunch

The choice of oil will not influence basic operation. It is not the source of your loss of power. The system should operate on any decent UTTO if properly filled and free of other mechanical issues. I am not disputing Whitetigers assessment of the value if UDT2 in this application but it should function with anything even remotely close.

Dan

 

[bruiserstone75]

Hello All,

Just to follow up and close out this thread, I sent my ZD211 to the local Kubota dealer. Took about 4 weeks to repair, but they finally diagnosed the issue as being a worn lift pump. Just got it back yesterday and so far, so good! Thanks to everyone who took time to respond, appreciate the help!