Leak Down Rate On Loader?

robertm · May 18, 2004

So, I contact Kubota directly about the leak down rate of my B7500/LA272 loader. They tell me 32 inches (empty) of fall in 6 hours is "Normal", and to the floor in 12 hours is also "Normal". I understand this spool valve is not precision equipment, but I think, as well as a few other dealers, think this is NOT normal. What are all of you experiencing? I don't use the loader as a scaffold or anything like that so it really doesn't matter, but when I have to keep starting the tractor to raise the loader when I use it to scrape the MMM and change the blades, I get irritated. What's up with that? Thoughts anyone?

MarkLeininger · May 18, 2004

Hi Bob,
That's about like my JD. If I stop to talk with someone with the bucket up, it will drop an inch or two every 10-15 minutes. Don't know what normal is supposed to be.

To20Chris · May 18, 2004

On my Rhino 2408, leakdown is imperceptable over at least a week (empty). Same with the 3ph with a BB on it. The backhoe does move some though.

Will_C · May 18, 2004

That sure seems excessive to me. My brother routinely leaves the FEL on his B2400 in the air for long periods of time with no perceptible drop. I know I have left the loader on my BX 2200 in the air for 1-2 hours with no more than an inch or so of drop.
Will

frank_f15 · May 18, 2004

i can't tell u what is normal, don't think anyone else can either. my b2400 will drop the bucket from a foot off the ground in an hour or so whereas my friends b8200(14 years old ) holds steady, the tractor dealer in town parks some of his with the buckets fully up and they never seem to leak down. My 3 pt. tho, will hold my finish mower in the raised position overnight without dropping an inch.

8561 · May 18, 2004

Robert - I experienced exactly the same thing. I have a B2410 with a 352 loader. Both my dealer and I thought it was in the loader valve. I removed it and and swapped my loader valve for a new one. The bucket still leaked down excessively. Turned out it was one of the cylinders leaking by the seal internally. The quick way to tell is to raise the bucket up and shut the tractor off. Remove the hydraulic return line on one of the lift cylinders. A little fluid will come out that is in the line. If fluid continues out while the bucket drops, that's your leaker and your problem. Remove the cylinder from the loader and have it replaced. If not, hook the return back up and try the other side. Between sides, it might be a good idea to start the tractor and cycle the loader up and down to work out any air. My guess is you have an internal seal in a lift cylinder that's not holding fluid.

uhmgawa · May 18, 2004

( So, I contact Kubota directly about the leak down rate of my B7500/LA272 loader. They tell me 32 inches (empty) of fall in 6 hours is "Normal", and to the floor in 12 hours is also "Normal".)

Kubota has a wide range of what they considerable acceptable.
Frankly what you describe sounds rather excessive.

( I understand this spool valve is not precision equipment, but I think, as well as a few other dealers, think this is NOT normal.)

Actually the valve spools and bores are precision ground. To such close
tolerances that valve housings mount with three bolts rather than four to
avoid racking the housing and causing the spools to bind in their bores.
That said there is some daylight between spindle and bore so oil under
pressure does have a leak path.

( What are all of you experiencing? I don't use the loader as a scaffold or anything like that so it really doesn't matter, but when I have to keep starting the tractor to raise the loader when I use it to scrape the MMM and change the blades, I get irritated. What's up with that? Thoughts anyone? )

It may be also be the cylinder seals have worn. With some effort you can
plumb in a A/B selector valve or high pressure ball valves to determine if
the cylinder still drifts when the spool valve is factored out.

kubmech · May 18, 2004

Leak down rates vary across a pretty wide spectrum. I remember when I was working primarily on Deeres they had them published and I was pretty suprised myself at how much was "allowable". One of the biggest culprits was the Husco valves they were using at the time (which Kubota still uses, not sure about Deere anymore) and there tolerances did vary quite a bit. Now the simplest way I know to test a hyd cylinder for internal leakage is to remove one hose from one side of the cylinder if it's a bucket cyl. remove the upper hose and cap off the hose. Then curl the bucket all the way back and hold the control valve against relief, after the cylinder stops travelling you should see very little to no fluid coming out of the open port of the cylinder, when I say very little I would put that at one drop per minute. Any more than that and the cylinder piston seal is leaking or there's a problem with the cylinder barrell or piston itself. Same with the loader lift cyl's. If all cyl's check good using this method then it's in the spools of the control valve. 90% of the time the spool valves are fine and it's cyl. internal leakage that's causing the problem, however like I said if the day that spool was matched to the valve was'nt a good one you will be dealing with tolerances that are a little loose and the only fix is to hope for another valve that was built a little tighter. Now some are under the assumption that if they replace the o-rings that seal the top or bottom of the spool it will fix there problem...well don't go there, those o-rings have nothing to do with this problem. Like I said it's the way the valve was machined to match the spool that will cause this leakdown problem if the piston seal in the cyl is not at fault.