Landing Gear Issue, 1967 T337B

OhioSkymaster · #1 03-01-22, 02:30 PM

Thanks for the suggestions. My main concern is the gear handle issue. If I understand correctly the switches only control operation of the indicator lights and not the handle, so the indicators may actually be correctly showing that the gear is not fully stowed. We did a number of gear swings at annual time just last month and had no problems. We used a homebuilt "mule" built from a pump removed from a 337 and driven by an electric motor. I'm wondering if the pump may be suspect. We did check the fluid but will re-check and check for air. Had the same problem just before annual, so it wasn't introduced by connecting the mule.

Jhogan0101 · #2 03-01-22, 02:35 PM

I recently had a problem with air being introduced into the system, fluid was foaming out of the front hydraulic vent. The lock nut on the return side of the pump was loose and sucking air in like a venturi. I doubt this is what youre experiencing but who knows.

GAdams · #3 03-01-22, 06:22 PM

I had some loose nuts in the system and yes it does induce air. The handle is all about pressure. Put a wrench on every nut you can find. Top off frequently. Bleed the system again and again. Put the plane on the ramp and run the front engine. Put the handle down. Wait for it to retract. If it doesn't purge then fill, purge again. Repeat. Once you get the handle to return from the down position. Go fly it. Land. Do it again. Repeat as necessary. Many Many Many times.

wslade2 · #4 03-01-22, 11:48 PM

Check the hydraulic screen and relief ball valve for clogging.

If you’re sucking air, it can make the fluid foam. Foamed up fluid is more compressible and won’t actuate the system firmly. ie-may not get firm up operation leading to unexpected lamp indication. Foamy fluid can come out the vent. Look for hydraulic fluid on the ground under the vent or streaking under belly of plane.

I capped off my pump and hooked a hand operated vacuum pump from auto part store to the other port to check for air leak at pump. If it doesn’t hold vacuum, you’re sucking air at a worn pump shaft and bad internal seals.

If you’re on jacks, you can operate your on plane pump with splined socket from harbor freight hooked to a 1/2 inch drive drill and observe for issues.

If you unhook the lines from your pump, you can fill the intake side with hydraulic fluid (I use a hand pump oil can from tool store), then turn the prop by hand. A good functioning pump will move fluid to the output side efficiently and directly. You will see smart fluid movement without a lot of prop movement once primed. Observe for sluggish or no flow.

Look for hydraulic leak anywhere and everywhere. What wasn’t leaking before can be leaking now. I did high speed taxi this weekend to check some brake work and darn if it didn’t make a door actuator start leaking that wasn’t before.

OhioSkymaster · #5 04-17-23, 10:53 PM

Still fighting this problem. Tried the bleeding process mentioned below, no joy. We recently jacked the plane and, after some false starts, found that the right mains up switch was not functioning properly. The plunger of the switch was depressed per the manual, but we found that it was open-circuit when measuring voltage around the daisy chain. I pressed on the switch plunger a bit and, lo and behold, the switch made contact and I heard the door actuator solenoid engage. We replaced the switch and cleaned the terminals. Under test with a mule (electric motor driving the same type of pump as installed on the plane) we cycled the gear 10 times and it worked perfectly. Then I flew and had the same darn problem. The pump was recently rebuilt by Aircraft Accessories of OK, us thinking that it might be the problem but no change. Any ideas? Also, any recommendations for a shop in or near Ohio with expertise on the Skymaster landing gear system?

hharney · #6 04-18-23, 05:23 PM

Check with Griswold Aviation in Marshall Michigan KRMY
(269) 330-2908 Craig the owner knows the system very well

wslade2 · #7 04-18-23, 10:48 PM

Thinking about this problem I am going to compartamentalize.

When hooked up to the mule, system works fine. When hooked up to engine driven pump, it doesn't. Sounds like (at least now after your switch repair) everything from the firewall back works ok-because it does on the mule. The pump has been overhauled. Provided the overhaul hasn't failed, or the pump is not being spun at adequate rpm (unlikely), your problem is basically between the pump and firewall. Not much there, except the connections.

In one of my other lives, having dealt with heavy duty diesels, it's amazing what impact a fuel line suction leak can have on operation of the fuel pump and engine. ie-a little suction air leak into the fluid stream can dramatically reduce the fuel pump output.

Maybe check carefully your suction line. Maybe pressure test the suction line for leaks? What I also recall is that the fittings on the pump involve compression nut, oring and a teflon back up ring. Are these all in good shape/new? How many years has that o ring been compressed under that nut loosing some of its sealing capacity?

Also when you switch from mule to engine driven some air can be introduced.