L3400 Weak Power steering

J252 · Apr 17, 2011

We have recently acquired a used L3400DT w/ loader to replace an older L345DT.

I think I may have a weak power steering issue. Doing field work, when I am trying to turn around, the power steering feels taxed. Specifically, when I am trying to turn the front wheels in soft soil (when stopped) the power steering system get overtaxed and can't overcome the drag load and I can't turn the wheel any farther.

I first suspected air-entrainment so I removed and checked the rubber hydraulic suction hose but I couldn't see any obvious holes or cracks in that. I will likely replace it anyhow.

I now have the feeling the relief valve on the power steering system is set too low.
Has anyone come across that before? I doubt the pump has any issues since the tractor only has 120 hours on it. I don't have a gauge setup to check this.

The other possibility is that this may be normal operation though I somehow doubt that this is all she has, since the old L345DT seemed to have more grunt in the power steering when doing the same work.

teg · Apr 17, 2011

I would be very surprised if it's NOT the return hose by your right foot. I used duct tape on my hose while I had one on order. It sucks air in, does the FEL work perfectly? That would be a quick and easy test.

What RPM were you running when it stopped steering? 1500+?

J252 · Apr 18, 2011

I was working well over 2000 rpm. I think the problem came about after working for and hour or so, or at least that's when I started to notice it. I did try the loader (empty) at that point since I immediately suspected the suction tube. It did seem to move up OK, though the fluid flowing through the lines did sound more "hissy" than usual. Is that a sign of air entrainment?

If it turns out to just be the suction tube, I will be very happy. It's just that when I took it off, I couldn't find any flaws in the old one. It's not painted gray so it's been replaced at least once. Nonetheless, I'll order a new one anyway and swap it next weekend.

ssmith general · Apr 18, 2011

I assume you're in 4wd.

My PS gets taxed in a lot of heavy turning in deep dirt with not much forward or backward move movement. This is normal and can be attributed to operator error. With more practice planing my turning, it doesnt occur. Think about the force needed to turn those tires when they are down in the dirt. I think my PS works better than I would expected in those situations.

J252 · Apr 19, 2011

ssmith general said:
I assume you're in 4wd.

My PS gets taxed in a lot of heavy turning in deep dirt with not much forward or backward move movement. This is normal....

It's possible for sure, but I'd be really surprised if this thing had a weaker power steering system than the old L345

J252 · May 1, 2011

I did not replace the suction hose.

So, I used the tractor again today. More field work for a couple of hours.
When I first started working, the power steering worked great. After some time (an hour or two) I noticed the steering getting weaker. Again, I tested the loader (empty), and found that it sounded quite hissy.

I think the hyd. fluid is getting aerated. The fluid does not seem to be getting too hot, or at least it doesn't feel like it when I touch the hard hydraulic lines below the seat. Warm, but not not unreasonably so.

I now have 3 different theories I'm thinking about:

1) My sight glass looks like the trans is slightly overfull. I say slightly because I see a bubble in the upper part of the glass. Maybe the high level is causing aeration in the fluid?

2) I used a generic brand tractor Trans/Hydraulic/Diff fluid. It said on the label that it is Kubota UDT compatible. Maybe its not as stable and viscosity changes too much with heat?

3) Even though the suction hose looks perfect, it might be leaking a minute amount (like a pinhole) and it takes some time before it entrains the oil with enough little air bubbles to make a difference?

Chilly807 · May 1, 2011

I think you'll find no difference after changing the hose, my power steering acts the same as yours does. As soon as the tractor moves even an inch or so ahead or back, it's fine, will turn the wheels with no problem. Sitting stopped, if the ground is resistant to the wheel turning sideways, it won't.

I think it's possible Kubota sets the relief pressure low to prevent dismounting the front tires if you're up against something solid.

As far as I know, there's no problem with the suction line on my tractor.

Sean

kuboman · May 1, 2011

I am sure you will find that this is normal operation. The reason it seems worse after operating for an hour is because the oil has warmed and thinned some. If it was set to turn no matter what then there would be breakages everywhere. The system is designed to not break the steering when the tractor is not moving. Heavy loads on soft ground is very hard on the steering.