Leak in slide-out Hydac valve causing landing gear to sink?


Well-known member
A few days ago, the front landing gear on our 2013 Landmark began to sink. They dropped 7 inches from level overnight. The rear and middle jacks extended as the front dropped, so all six of the Lippert Level-Up pads were on the ground.

I found a small puddle of hydraulic fluid in the front generator compartment under the Lippert hydraulic manifold. Further investigation revealed that the Hydac cartridge valve for the kitchen slide-out on the manifold was leaking. There do not appear to be any leaks around the landing gear themselves.

I've ordered a new Hydac cartridge because that one obviously needs to be replaced if it's leaking. But I'm wondering now if the leak from that cartridge is the cause of the landing gear drift-down, or if there are two separate problems.

If the Hydac cartridge for the kitchen slide had an internal clog or malfunction in it that caused it not to close completely, could that bypass allow hydraulic fluid to bleed from the front landing gear back into the rest of the system? I know that the landing gear has its own Hydac cartridge valve, but the valves for the rear jacks are on the same manifold as the slide-outs, so I don't have a complete picture of the plumbing.


Well-known member
With 6 point level up, there are usually 3 control valves; one for both front landing jacks. A second for the middle and rear jacks on one side. A third for middle and rear jacks on the other side. If those valves are closed completely, no fluid moves and the jacks will move only if a jack has a leak. So, a leak in either front jack will allow the weight of the trailer to push fluid through that leak. The leak could be at either end of the hose going to the jack, or inside the jack. A partially open control valve would also allow the front jacks to be collapsed by the weight of the trailer.

A leaky front shouldn't compromise the middle/rear jacks on either side as their valves would still be closed, preventing fluid movement.

A problem with the jacks shouldn't affect the slides or vice versa, other than perhaps to leak enough fluid that what remains in the tank isn't sufficient for proper operation.

I've not heard that a malfunctioning control valve would itself leak fluid outside the system. Normally a leak at the valve would be from a loose connection or a bad crimp on the hose. But perhaps I've not heard everything there is to hear.


Well-known member
Thanks Dan. That's where I'm confused. On my system, the control valve for the landing gear is on the driver's side landing gear itself--it's not even on the manifold with the slide-out valves. (The two valves for the left and right mid/rear jacks ARE on the manifold though.) So I'm wondering if there are two separate problems: a leak in the valve for the kitchen slide, and a sticking valve for the landing gear. It's just odd that they'd happen simultaneously... I guess I'll have a better idea once I replace the kitchen slide valve. If the landing gear sinking continues, I'll know it was a separate problem.


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Circling back on this. I replaced the hydac valve for the kitchen slide, and that stopped the leak of hydraulic fluid in the generator compartment. I don't know if it was just one or more bad o-rings on the valve that caused the leak--that seems to be the most likely explanation since I can't see anywhere that fluid could get out of the valve externally. But in any case, that problem is solved.

For a month or so after that, the front of the trailer didn't sink. However, a couple of days ago, after operating one of the slide-outs a few times for an unrelated issue, both front landing gear sank rapidly (several inches over the course of a few hours). I re-extended the landing gear and the same thing happened, and that has repeated several times. I'm now back to supporting the front of the trailer with jack stands under the frame.

So there is obviously another problem with the landing gear that I haven't solved yet. When the landing gear sinks, hydraulic fluid is being returned to the reservoir, so it's not an external leak. That points to either the hydac valve on the road-side landing gear not closing all the way (either a bad valve or debris in the orifices), or an internal leak in one of the landing gear hydraulic cylinders.

Edit: following Lippert's instructions for testing hydraulic cylinders, I found that there's a leak on the left (road) side. During the test, fluid came out of the Extend port on the landing gear while the pump was pressuring for retraction, which shouldn't happen. Does that definitely indicate that the hydraulic cylinder is bad, or could the same symptom be caused by the hydac valve not closing? Is there a way (short of just replacing the hydac valve) to isolate the problem to one of those two components?
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Pennsylvania Chapter Leaders-retired
Thanks. Thought so but wanted confirmation.
I’ve experienced front jack drift on both travel days and when extended on a site pad
I have the lippert instructions too. They say it’s a bad seal in one of the front jacks. I replaced leaky hose hoping that was the cause but it wasn’t