Hydraulic leak - can't find the source

[AV8ing]

I've got a 337D that's been leaking hydraulic fluid from the belly for some time, usually dropping 5" to 10" puddle but only after 7 to 10 days AFTER last flight.

I've pulled up the floor and there's hydraulic fluid just about everywhere from firewall to firewall !

Many hours and a few liters of white spirits and gas later I've gotten the mess cleaned up.

So I've jacked the plane and swung the gear multiple times and can't see any leaks.

Two weeks later, I've got more fluid and a puddle under the plane.

Wash - rinse - repeat and still unable to find the source despite using mirrors and borescope ....

That said, it appears to be under or near the main actuator , but I haven't actually been able to positively confirm this.

I don't want to pull out the main actuator unless I'm 100% sure it's the culprit.

Running out of ideas - any help appreciated !

[Rick Erwin]

Try cutting about 3”x3” squares of white pig mat and place under each hydraulic joint to see what shows up.

I’m doing the same thing right now.

I’m thinking that should help to narrow down the location.

Rick

[Skymaster337B]

My experience with that kind of leakage is the main gear actuator. It’s the only one big enough to put out that much fluid in the belly.

It happened to me. I overhauled the main actuator and discovered the back-up ring was installed the wrong way. It came out of the factory that way. But still worked for 50 years.

[AV8ing]

Skymaster337B - That's my current thinking and I'm pretty sure it's been going on for many years.

Did you overhaul your actuator or send it out to Cox or another Repair Station ?

[wslade2]

I had a belly leak that was dripping from seam in belly skin. Similarly left a hydraulic stain about size dinner plate after a week. Floorboards up and hydraulic fluid all over from front to back by mains actuator.

After clean up and quite a bit of time (hard because the fluid weeps everywhere) finally found I had a drip from the emergency hand pump. At first didn’t suspect it because your brain goes to the worst case scenario, kept examining the main’s actuator.

I finally found via a good clean up and using a flexible scope (like from harbor freight, very affordable). I would see wetness in the well around the shaft. Suck it out with corner of paper towel. Wait a while, scope it and start seeing the fluid build up in the shaft well. The scope magnifies things making the tiny leak findable.

The pump was an easy rebuild. Just some o rings.

[AV8ing]

Wslade2 - Actually, I started with the hand pump since I used to own a Cessna 210 and the only hydraulic fluid leak I ever had was from the hand pump.

I can say unequivocally that the hand pump is not leaking.

So will probably bite the bullet and pull the actuator next week.

Any tips on rebuilding the main actuator ?

[Skymaster337B]

Originally Posted by AV8ing

Skymaster337B - That's my current thinking and I'm pretty sure it's been going on for many years.

Did you overhaul your actuator or send it out to Cox or another Repair Station ?

I overhaul it by removing the aft end. It unscrews like a jar top. Then Jack it to pull the piston out.

[AV8ing]

Finally found the leak(s) ! ! !

Turns out it was the up-lock actuator - the last place I looked, all the way in the back under the rear seat rail. I can't believe that it made the mess that it did, that said there's no doubt it's the source.

Has anyone compiled a list of O-rings and packing required to overall ALL of the gear actuators ?

So The plan is to overhaul all of the main gear actuator except the big main actuator that's dry as a bone.

Thanks!