Hydraulics slowly quit working

[Carlaisle]

This Kubota L345DT's hydraulics become slower and slower the longer it is used until they completely stop. No 3 pt lift, no auxiliary, no steering (it uses a double pump with the front pump powering everything except the power steering and the back pump powering only the power steering), nothing. Engine is not laboring, filter is clean as a whistle, fluid level is good, outside temperature has no impact on the issue. If you go take a long lunch and return to the machine, it works fine. Seems to suggest something is overheating and needs to cool down, but precisely what is not readily apparent to this non-expert.

I picked this machine up used and it has had this problem since day 1. When it first happened I inspected the filter and found it installed incorrectly (it's an internal screen, not a spin on canister) and plugged nearly solid. Cleaned it, put it back together, worked fine - but it had cooled down by then. I've checked the filter since the initial discovery and it's spotless. Does anyone have any suggestions?

 

[K5lwq]

I would suspect the pump. I have bought some time using Lucas Hydraulic Booster & Stop leak. I would add a gallon to the system and see if that helps. I have bought it before at TSC. Works good for what it is.

 

[RNeumann]

If the original filter was that plugged and suddenly everything is spotless I’m thinking something was missed. Internal screen or a second filter? Have you put a pressure gauge on it- is the pressure dropping or (my guess) is the flow restricted? Working but slow could be a flow issue instead of a pressure issue. My SWAG is something is plugged! But I don’t know that model to be able to point to the common causes. It would seem unlikely that both “sides” of the pump would fail at exactly the same time with exactly the same issue- again that’s my SWAG

 

[Carlaisle]

Appreciate the responses. My logic may be flawed here, so feel free to poke any holes that may be needed in my theorizing. If a hydraulic pump is worn, it should have greater than desired/engineered tolerances. This would suggest to me that performance would be poorest when cold. As everything warms up, tolerances should close up and performance improve. This seems to be the exact opposite of what is happening.

As RNeumann mentioned, it seems extraordinarily unlikely that both sides of the pump would fail at the exact same time. That sounds more like a supply problem. The shop manual only shows the one filter, although that's not to say there isn't another covert operative in play somewhere...

Here's an interesting thought. I think the power steering pump has a separate reservoir from the main pump. Unfortunately, if true, that just leaves me more in the dark as to what might be the cause of this problem.

 

[riderpriderking]

I think tolerances actually open up once warm because the fluid becomes less viscous, or thinner, which allows it to squeak through leaks. I had an o-ring blown on my tractor and so the hydraulics progressively got worse as fluid more readily squeezed through where the o-ring was supposed to be. Mine obviously only affected everything downstream of that o-ring, in your case it seems to be affecting everything which is why a pump seems plausible. Pumps do tend to last a while though so unless it's a fairly old tractor I'd be looking for something else before I went out and spent the coin on a pump.

 

[K5lwq]

In my case, as the fluid heated up it thinned out. This would cause the hydraulics to be very weak. If I ran at full throttle I could use but would barely lift a bucket of dirt. I added the Lucas and it made a big difference. That stuff is thick and it seamed to help other things like the brakes.

I have since replaced my pump but I used the Lucas for more than a year without any issues.

Hopefully you will find another issue that is less expensive fix, but doesn't hurt to give that stuff a try.

 

[dannoGT]

Interesting problem I am assuming that when you say double pump that you mean it has a common shaft running through the pump ? And the pump has front section and back section with a seal between the two sections? Could that seal be leaking?

 

[Carlaisle]

It does make sense that the fluid could thin more as it warmed up than the tolerances tightened up. Viscosity is much more temperature sensitive than metal.

Sounds like an easy test I've yet to perform that may (or may not) be instructive is to see if revving the engine up will overcome the loss in hydraulic function to any degree. I'll try to remember to try it the next time it happens. Needing to work it for an hour+ before the problem presents itself frustrates the whole diagnostic process...

I've used the oil thickener in a worn out engine before. It ran just fine like that for several years until I got around to rebuilding it.

 

[Carlaisle]

Interesting problem I am assuming that when you say double pump that you mean it has a common shaft running through the pump ? And the pump has front section and back section with a seal between the two sections? Could that seal be leaking?

Correct. A single drive shaft enters the front (main) pump and drives both. I suppose there would have to be a seal on both ends of the shaft. There's no leakage to the outside of either pump which seems like it would eliminate that as a possible cause.

 

[Carlaisle]

I just looked up the price of that pump :shocked: