Leaky Shock Struts

Helidesigner

Helidesigner

Helidesigner
I just completed my annual conditional inspection. I checked the Automatic Transmission Fluid (ATF) in the shock struts and I was pretty low. I filled them to the top fill hole. I did not notice any difference in the gear behavior before or after. However, I did immediately have some leaks. The day after a flight I had a small drip puddle under each gear fairing. I took a look today and the top of the strut where the large spring clip retains the metal insert is all wet. The gritty stuff in the picture is dirt and stuff from my shoes that works it way down there. The fill plug is dry. It looks like the fluid is being forced out around the spring clip, then it runs down the strut, gets on the gear fairing, collects at the lowest point, then drips on the floor. Has anyone else had this problem? Is this what is happening? I have yet to have a particularly hard landing in 320 hrs so I do not think it is landing damage. Is something worn?
 

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Some folks have had them leak at the rod end bearing threads. Did you put any loctite on those? Perhaps your o-rings are leaking?
 
jaredyates said:
Some folks have had them leak at the rod end bearing threads. Did you put any loctite on those? Perhaps your o-rings are leaking?
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Agreed - mine leaked at the threads immediately, until Mark G. advised I use thread sealant there.

Lucky for me I noticed this about 3 days into the build . They have NEVER leaked a drop since then, despite all kinds of heavy work-outs.
 
I have wondered about this. It seems like it might be possible to overfill when the strut is extended some sitting on the ground. When the strut retracts after takeoff, I am thinking it will decrease the volume available for fluid. If this is happening, then the leaking would only occur in the air but residual fluid might take a while to run down thriugh fairings. Also if this theory is correct, it should stop leaking pretty quickly once the small excess fluid is pushed out. No problem so far on our Patrol.
 
Good point Ed, I have always filled mine with the strut removed, but with a little load, the volume of the fluid chamber is increased based on the amount of piston that is outside of the seal. I had never thought of that.
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I see fluid on the threads. I did not use sealant. Maybe, hopefully, that is the problem.

I was looking at the drawings. Frankly I can't figure out how the fluid moves under spring deflection. There are no holes in the lower cap. It looks like the piston will try to compress the fluid. If the entire cavity is full, including the center of the inner shaft, there is no air to compress and the fluid can not migrate to the bottom of the cylinder. What am I missing?
 
Helidesigner said:
I see fluid on the threads. I did not use sealant. Maybe, hopefully, that is the problem.

I was looking at the drawings. Frankly I can't figure out how the fluid moves under spring deflection. There are no holes in the lower cap. It looks like the piston will try to compress the fluid. If the entire cavity is full, including the center of the inner shaft, there is no air to compress and the fluid can not migrate to the bottom of the cylinder. What am I missing?
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There is a tiny pinhole drilled in the bottom of the plunger, that hole is important for making the whole fluid-damper system work as far as I can see.

If you can't see a tiny hole somewhere there on the plunger, then that would definitely be part of the problem.
 
There is the big hole (almost 3/4") on the very bottom which is the I.D. of the piston shaft, and the 5/32" hole a few inches up the piston shaft. Mark
 
OK, I see it, thanks.

How do people support the plane if one or both gear leg struts are removed? Do people support the plane with a vertical wood or other strut directly under the outboard wing strut attachment point to unload a gear leg?
 
Safest way seems to be to lift it at the engine mount and maybe stabilize it at the strut attach points. I've seen posts where people have lifted it the way you described, but I would think that would be for a short duration lift like for a tire change where the gear can still support it if something happens. It would really suck if it slipped while you have part of the gear off.

I think I used fuel lube EZ Turn on my rod end bearings, I figured its good against petroleum products and will still be good later when I have to adjust it for length to get the gear width right.
 
I was just doing this to swap out my original streamlined struts for new ones with a round cross-section. Bob recommended to run a beefy ratchet strap or come-along across from one tire to the next, you can pull the gear together to a point where the shock struts are unloaded. Use some soft rope to give the device something to attach to without scratching up your gear legs. Roll the plane a little as you tighten it if you are working in an area where your tires have good traction, or provide some sort of traction reduction. He said he has used two pieces of countertop formica with grease between them. I work on a gravel floor, and with a little rolling it works out.

Once the gear is unloaded, you can remove one strut, service it, and reinstall it before repeating the process on the other side. You can also connect an engine hoist and lift the nose up, but if you do that, don't remove both shock struts unless you have a plan to keep the airplane from banking. If you have a helper ready with a wooden support, when it starts to roll, they can identify the heavy side and prop it up. As for products, Bob has said that in the past that he likes blue loctite there, and that if it is necessary to eliminate the jam nut in order to get the right tread width, the loctite is also an acceptable substitute for the jam nut. Don't forget that there is a bushing inside the upper rod end bearing that may be inclined to fall out on the floor if you remove that top bolt. You might be able to complete this job without disconnecting the rod end, by rotating the shock strut around the stationary rod end.
 
I filled by Patrol shock struts up to the tippy top about 4 months ago and installed them onto the fuselage. I did not seal the rod end bearings, and they both have been leaking very slowly since. There is no weight on the gear other than an empty fuselage cage. I thought by now the leaking would have stopped. My theory is the cylinders are under no pressure and the cylinders are held up with the spring pressure. But they are still leaking.

There is a way to seal up the rod end bearing threads by removing the rod end bearing, and installing a hex cup point socket set screw (that with 1/2" - 20 threads, and 3.8" long) with sealant. Install some sealant down inside the threads with a straw, then install the set screw all the way down. I did not do that with mine because I was concerned about having that set screw down there and taking up space that I might need for future adjustments of the rod end bearing. I also wondered if I would forget that the set screw was hidden down there. For now its a trick I might use if they never stop leaking....but I think the laws of physics will stop the leaking at some point.

Or am I wrong? Is there any force behind the fluid pushing it?
 
Jared, I like the strap the gear legs together idea. I think that will work. The trick seems to be getting just the right amount of travel so the strut does not lock up hard in compression.
 
Helidesigner said:
Jared, I like the strap the gear legs together idea. I think that will work. The trick seems to be getting just the right amount of travel so the strut does not lock up hard in compression.
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Just make absolutely certain you don't remove both struts at the same time! The gear legs will collapse.
 
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