Oil in Belly
 

My 1969 D Model has fresh oil IN the belly in front of the landing gear transmission. No further aft than 1 compartment and no further forward than two compartments. The color of the oil is yellow like. Same as fresh engine oil. I know the transmission has no oil in it. I also know the gear legs have no oil in them. Also the fluid used to actuate the landing gear system is 5606, which is red. I can't find the source and the amount is not very much but enough to pool. Does anyone have any thoughts? Insights? I've cleaned it up before and it comes back. Also it comes out of the weep hole in the belly compartment and streaks back in the airflow on the outside of the airframe.

Look carefully and find the pin-hole in the oil pressure line from the rear engine.

Dave

What he said.

metal oil pressure lines from aft, low likelihood of getting pinhole (pretty secure little movement to create a hole but could be possible). It's been a couple months since I looked at mine but see if there are any unions along the route of rear oil pressure line through the tunnel. A union might be better potential site of ooze.

Also, check where metal oil lines join flexible lines behind panel. Hose or union could ooze, travel along line until finds low point and drips into belly. (all this provided you still use mechanical gauges in panel)

Likewise look behind rear firewall under engine where the metal line joins the flexible feed line. An ooze at a union here could travel down follow the turn in to the tunnel, and drip off of a low point. (My thinking more likely than above.)

I discovered an ooze at flexible-metal line union behind panel just like that a couple months ago. Didn't pool but was making metal line wet/sticky with oil and everything else close to it too.

Those flexible lines behind panel out of sight out of mind-can get old, deteriorate, crack or worse. Might be good time to inspect them or replace if old/unknown age.

The oil pressure lines from the motors are copper lines. They are prone to cracking. Over the years they lose their ductility. There are no unions in those lines until they meet up with the barely flexible lines at the inside of the front firewall behind the gauges.

A good test is to pull the line from the rear motor at the T on the passenger side in the middle of the case. Pressurize that with your nitrogen tank to no more than 50psi. You can T in a tire pressure gauge to that test line too. This will facilitate finding a leak and give you an idea of the accuracy of your oil pressure gauge.

In performing this test to repair a leaking oil pressure line in the belly I found that the response of the oil pressure gauge is poor. Below 30psi the needle didn't move. At 50psi it slowly came up. I flushed out the line with solvent but it made no difference.

Dave

Superior idea!

Correction
 

The information I wrote last night about the oil pressure lines was absolutely wrong. The oil pressure lines are made from aluminum tubing. There are a few unions along the entire route. For some reason I was thinking about the copper primer lines. The aluminum lines can leak at any of the unions. Look closely for any splits in the flared aluminum pieces. My oil leak was a pin-hole in the middle of one of the aluminum lines. It was not rubbing on anything.

I am sorry for the previous mis-information.

Dave

Liquid grease
 

I cannot find an oil leak. The gear transmission or what ever you call it has grease installed at manufacture. Perhaps it is a grease that has exceeded its temperature limit. 200-500 F. If so what’s making it so hot? The oil as described is a yellow color and now the oil in the engine has a few hours on it since the change. Ideas?

is your oil level dropping? Is your hydraulic fluid level dropping? I believe you are describing the main gear actuator. nothing should make the grease that hot. Could it be grease wetted/mixed with hydraulic fluid? ie, maybe you have hydraulic leak of main gear actuator. Also, brake line passes through that area. Old brake fluid can look funky. Brake function? Brake fluid level?

Hot Grease
 

Oil level is not dropping. Hydraulic fluid level seems to need servicing occasionally. I can always tell because the left main gear door pops open. Put a little fluid in and its fine. That has stabilized. Hydraulic power pack was overhauled less than one year ago. The fluid doesn't look polluted with another fluid or dirty such as old oil. Brakes work no leaks, not the greatest stopping power. If you clean up the belly inside and remove the fluid from the bottom of the aircraft it returns on the next flight. Yellow, consistency like a thick oil and doesn't really have much of a smell.

I would look at the gear door actuators, start with the left main and keep going.
They have to be rebuilt just like the powerpacks...I think Rick Cox did mine.

as per Rambo
making a list, 4 fluids in the airplane: gas, oil, hydraulic, brake (also hydraulic)
it's not gas collecting
oil level not dropping and if you did Dr Dave test, that's out
brakes not great: possible
hydraulic needs topping off (must be going somewhere) and gear door dropping-suspicious
I had a very small leak from my emergency hand pump. By the time the hydraulic fluid mixed with the dust and grit in the belly it was black, not red, dripping out the weep hole. Don't count on the color. I ended up using scope to confirm hand pump was the source of the leak. You can get from harbor freight and on occasion have seen at hardware store.
Chase what you know is wrong. Hydraulic fluid is going somewhere. Plus I would put a hydraulic leak pretty high on the list of something to investigate whether or not it's the problem in the end.

Okay, let me add one more thing. I promise this won't be wacky like the copper line mistake. We developed a small collection of oil in the center bay of the floor under the gear actuator. The oil would also drip off the left gear leg door if it was left open. I put towels under the motor for a couple of days. After two days the towel under the sump quick drain was wet. The oil was running off the sump drain and down the inside of the lower cowling into the belly.

I tried to attach a picture. Hope it works.

Dave

Picture of oil and area
 

Here is a picture. It's not oil, it's not 5606, it's not fuel. My mechanic's theory on the hydraulic fluid disappearing after the power back overhaul was, air bubbles were stuck in the system and as the gear was cycled the hydraulic fluid needed filling. The hydraulic level has stabilized an I have not added hydraulic fluid in quite awhile. He may be right. I don't know. I appreciate all the input. Please keep it coming.

Mystery Fluid
 

Based on the picture - it sure looks like engine oil...if not pin hole in pressure line, then it is breathing out of front engine or leaking like Dr. Dave's issue.

Is it sticky? I have seen old contaminated 5606 (Hydraulic fluid) take on a yellow color before...very rare but it can happen. OR - Did someone put a different fluid in your brakes?

I have personally just purged my brake system after resealing my brakes and installing new flex lines. I have one of those brake bleeding pressure pots from ATS, and I took a polyFlo fitting and screwed it (pipe thread) into vent hole on the top of the master cylinder. Off the polyflo fitting I attached a length of polyflo tubing into a container, and just pushed fluid up from the brake bleeder through the system with the ATS pressure pot. This flushes the whole brake line from the bleeder to the master cylinder. Once the fluid ran clean and fresh, close it all up and your system is clean, filled and bled all in one shot.

The area you have the fluid is coincidentally where the swivel fitting is for the brake lines.

Let us know...

Jeff

Fluid Consistency
 

It is not sticky but is a heavier weight feel to it than the oil I use in the engine. But I do recall seeing the same fluid running from the right side of the front engine several months ago. I'll check the fluid color in the breaks as well.

just as an experiment, I took some brand new red 5606 hydraulic fluid and put it on a dirty old paint can lid. Next morning it wasn't red. (I don't know why: because it spread out, dye evaporates, fluid evaporates or what.) Looked a lot like your picture.

Drying hydraulic fluid evaporates and thickens. More copious old hydraulic fluid very thick approaching gummy.

Your picture also looks a lot like what it looked like around my leaking emergency hand pump. I looked for a hydraulic leak and not an oil leak because that was what was most likely for the circumstances. I found a hydraulic leak and it stopped the problem.

5606 Hydraulic fluid is in the brakes as well as landing gear system.

Follow up on Oil in the Belly
 

I'm still trouble shooting the oil in the belly. We have discovered it is coming from the transmission that houses the worm gear which actually cranks the wheels up and down. Does anyone have a better name for this device? The hydraulic engine pump drives the worm gear based upon gear handle selection. When I select up it leaks when I select down it doesn't. I was trouble shooting why all the gear doors would not stay closed with the gear up. It turns out they will when the aircraft is on jacks and operated by a hydraulic mule. But when the engine pump is put on line and the fluid gets low in the reservoir the gear doors will not stay up. I'm talking a half pint low and bubbles are in the system. It seems when the seals leak on the transmission it draws in air when it is not under hydraulic pressure. Air being sucked into the transmission creates the bubbles and while it looks like you have sufficient fluid on the site glass it did not. Bubbles are bad for the system to work properly. The yellow fluid I was reporting is in fact older hydraulic and maybe it turns yellow because of the cavitation the system is experiencing. To get that transmission out is 2 days of work. The local mechanic won't open it up to replace the seals and wipes so off to the overhaul guy. $1700. Plus days and days of labor troubleshooting and R&R. Hopefully the gear doors will stay closed. Don't know.

Thanks for the follow-up on this issue - sure is nice to have some closure when people discover something like this. That main gear actuator (aka transmission) is a bugger to get out - but looks like you have solved the issue. Thanks again for sharing.
Jeff

Out of the shop
 

I finally got the old girl out of the shop. Doors close normally and stay closed. So Far...But not after some real gut wrenching trouble shooting. It took more than twenty gear cycles on jacks before the nose gear door would stay closed and some additional rigging of the nose gear door up actuator.

Glad you are making progress with that issue Gary.

So, did servicing the gear actuator/transmission seals fix the leak? I'm having the same issue of hydraulic fluid leaking from the belly. It's red, so no question of fluid type. After the last flight it leaked a puddle of fluid about 5 inches in diameter in just a few minutes after parking and shutting down, but after removing the interior and deck plates could not find any source of the leak. We're thinking of running the front engine and placing the gear lever in the Down position to pressurize the system and watch for leaks, before jacking and running the system with a mule.

I had puddle this weekend on asphalt. Opened gear doors and more dripped out. Worried it was the worst. Checked hydraulic tank and no drop in fluid. took up floor panels, hydraulic fluid everywhere. felt brake line and right where the flexible line joins the swivel on the gear it was wet. But that drip had worked it's way into the belly around main landing gear drive and everything seemed wet with fluid. That fluid has a way of crawling through seams and around everywhere. Confirmation came with checking brake fluid reservoir and finding it was empty. Be careful to identify your source so you don't do something excessive.

But, on next annual I plan on overhauling main gear drive just like I did nose gear actuator this year to be on the safe side. It's been untouched for 50 years....long enough.

Servicing
 

Servicing the actuator did work. You are on the right track by running the engine and putting the gear handle down and time the gear handle return to the normal position. Use the service manual for that procedure. If something is about to fail it will fail big time after 4-5 cycles. Getting that actuator in and out will be a lot of labor and getting the system primed will take way longer than it should. Also all the other seals in other actuators in the system that has not been touched will now start to seep because of the added pressure. Order some extra seals and be ready to chase door actuators and things like that. Word of caution. Jack the aircraft to remove the actuator. It must be off the gear or the gear will fold. My project took ten weeks from start to finish. But the gear works great now.

Leaks
 

Gents,
Had a similar event with oil on the floor, last month. It had been a few days after flying, there was a small puddle (2" diameter) on my hangar floor. (NOTE: I have resealed all my actuators, hand pump and replaced all flexible hydraulic hoses last year.)Oil had come out of drain holes in front of, and aft of, the handpump. I pulled up center floor board to note that the whole area was wet, and could not quite trace it to anything. started going upstream, and noticed it may be coming from pilot side forward. Looking at brakes, brake lines, etc, and did not see anything. Looked at power pack and did not notice anything major, but one line and a little fluid on it (not good). Looked in little drip tray under power pack, and there was a bit of fluid. Ran some mineral spirits down that tray drain tube, and voila - that confirmed the source. That drain tube does not drain overboard, but rather into your belly underneath the pilot's rudder pedals.
I ended up removing and overhauling my power pack - there was a hairline crack on the manifold at the "gear down" fitting.
Jeff

Thanks for the advice and suggestions! We will investigate further and I’ll report back to the group.

Well, it’s the main gear actuator. Any suggestions on sources for overhaul or replacement?

Cox Airparts.