Help-- Gear Problems (Hydraulic)

Sorry to say I haven't been much a follower of the message board for several months. Every thing working flawlessly logging 10-15 hrs a week! untill now. Hate to be that kind of guy... any-way glad your still here!!

Details... 1966/A 337 front pump only... After full fluid gear operates about 6 times flawlessly (10 sec. cycle time) after 6 cylces the gear will retract with all but the last door closing at which time gear handle stays up and all doors sag open, cyle gear down... no problems down and locked.
re-fill reservoir gear again operates with no problem 6 times. Corrective action so far has been replace all fluid, replace all lines, clean filter and yes belly is wet (red) no change in symptoms.

I hope some-one can help

Thanks again
Mel Smith (Guy with 3 children in T.C.pictures)

[WebMaster]

Of course we remember you Mel!!
My wife still has the hat that Chachi made her.

I would suspect that you got a leaker Mel, and while you can look at the things, it's going to take a mech to fix it. Ernie says he has a good one down at TMB, suggest you give him a shout.

Someone else can point you to a precise location, but it could be the hydraulic resorvoir, one of the hoses, or even the pump filter.

[SkyKing]

Mel,

If you've got a wet, red belly, you should NOT fly this airplane until you get the leak fixed... or you may find more on the belly than just red 5606.

Sounds like you have a slow weep somewhere in the system. Time to get out the Service Manual for YOUR airplane and read-up FIRST and go through the troubleshooting section.

You didn't mention it, but did the airplane just come out of maintenance or annual with some hoses being replaced, or did this problem just show up one day? Most of the time there are symptoms leading up the problem.

You should completely clean off the belly, then pull the landing gear circuit breaker and pump the doors open with the emergency hand pump. Visually inspect those areas you can gain access to with a mirror and a bright flashlight. Any Sears store or automotive store carries the small inspection mirrors. And we find the smaller flashlights with Krypton bulbs give the brightest light.

Since it sounds like your problem is related to the front hydraulic pump, check the hydraulic actuators and hoses in the nose wheel well area... up front you have the nose gear door actuator, the main nose gear actuator, and the up/down lock actuator, the latter which is back behind the nose gear on the pilot's side.

Let us know what you find... your exploratory efforts will help keep the expense to a minimum when it comes time to get your mechanic involved.

SkyKing

[Bob Cook]

Check actuator seals especially on front as they have the highest pressure.

bob

[Ernie Martin]

Hey Mel. Good to hear from you, even if it's due to a problem. Call my A&P, Luis, at 305-622-6849. My 1969 had the same problem and he fixed it fast. He's got lots of experience on your type of bird (less with my current 337G which has the electric powerpack). While he works on yours, we'll go flying in mine.

Ernie

Thanks for responding:

Ernie, I have made contact with Luis, hope to see you guys soon.

Sky-King to answer questions this has not instantly developed after service, first noticed 20 hrs into reservoir fill-up (intermitent).
Bob-- actuators are not leaking (externally!). After replacing hoses all panels were removed cleaned and inspected (nothing) wet belly is from reservoir overflow. My concern is a pump sucking air?? causing some sort of foaming? Or are actuators in need of re-build. Both scenarios could be expensive and un-necessary. Are these items field serviceable?? Proper (type specific!) Diagnosis is worth everything. Which I realize is one of the core values of our group.

Thanks again... Mel

[SkyKing]

Mel,

Doesn't sound like you have a Cessna Service & Parts Manual... most of your questions regarding the system and field serviceability would be answered in those pages... hint... hint!

SkyKing

[GMAs]

If you have checked the actuators... and they are not leaking then you need to concentrate on the pump and its inlet hoses... and the priority valve... as the rest of the system is pressure driven... no suction.. so air can get in from a actuator... through the actuator seals... pressure drives it from one side to the other... the only thing sucking is the pump from the resivor... and if the seal is leaking on it.. yep your going to put air into the system... and with air being put in.. it will force the retun fluid from the other side to appear like it is too much... easy to spot...
...

Here is how... with a mule... put the plane up on jacks... and run the system... if you find that the oil level remains the same.. then it has to be in the pump section..and its supply hose...and or filter.. if it changes... If on the other hand... it goes down and doesn't come back up when you cycle the gear.. then you have a hose or tubing leak... but, that would be easy to spot by pulling the keel beam cover.. and checking...with the red fluid being present... somewhere... now if the priority valve is leaking you would be getting air back into the system again... and it would burp the resivor...if no leaks...or burping... then were on to the engine dirven pump and its feed line from the resivor... now if it is the pump putting air into the system by leaking seals... you would be getting a contenual rise in the resivor level...when you cycle the gear with the engine runing... until it burps out the overflow tube... but, if you have a engine driven pump... unless the plane engine is runing you don't know...

here is a little way to test it... on the ground... with the engine runing test thing...

if you are runing the engine on the ground and the pump is circulating the oil from and back in the resivor tank... you would only get bubbles... inside the tank...now how can we check for that.. easy.. put a piece of tigon hose (rubber hose) on the outlet... overboard vent.. from the resivor tank...making sure the system is sealed up... caps tight etc... except for the overboard vent... and then put a little 5606 in a jar... put the other end of the hose into the jar under the oil... start the engine... and look for bubbles in the jar... if you get a constant stream of bubbles... your pump is leaking...and putting the air into the resivor tank... because it is presurizing the resivor tank and the air has to come out the vent... which it should not if it is good... now does that mean the pump is bad.. no... not necessarly... again we would go look at the supply hose to the pump and the priority valve... where the suction side returns to the pump/tank... pressure testing would not necessarly get you anywhere because this is on the sucking side to feed the pump... so it would have to be vacuum tested... and they make a little pump for testing things from the car section of the auto parts place... has a little guage on it to show when the leak is happening... capping off the pump outlet from the filter and applying suction to it by the feed line fitting... if it doesn't hold.. you got pump that has leaking seal... other wise advance to the the priority valve... will show if the O ring is bad at that end.. and allowing air to enter...


applying the suction tool to the feed line going t the priority valve will show if it is also leaking in the priority valve... as a second methode...

check the pump first... as they have been known to leak.. and usually its sucking air in... and foaming the fluid... with cause the resivor to burp...

So their is two ways to test the system... and one other thing that I would look at real close is the fittings...that feed the pump...too along with the hoses.. if some mechanic got a little too torquie with the fitting they can mash down the flair part... and it will leak... hoses can have a problem too.. but, I don't think the rest of the pressure systems hoses are the problem.. from your discription...otherwise you would find red on them as they are under about 1000 lbs pressure... when attached to the mule... no instead it got to be the pump or hose that feeds the pump or priority valve O rings..

Now leaving nothing to chance.. so we get a curve like ernie did... with his bad battery... you did put the right fluid in it...5606... no aditives... etc...

By looking at the service manual you can see where the lines are... and its in the supply lines that you want to concentrate your investigation...

Ya I am sure the mechanic with a enough time...will find it... too... with enough time... but, my money is on the pump seal, or its feed hose... for your air getting into the system...and forcing your fluid out... them pumps do get tired and while its out.. if it is the seal.. you want to check the shaft for clearance... because the seal leaked for a reason... old age... worn bushing... etc...

Start with determining that it is air getting in... by doing the vent test...in a jar thing... then go look for where it is leaking in... is your best shot... then do the suckdown on the pump.. and last do the prioity valve check... I am betting your going to find its the pump seal... sorry... G.M>GMAs

[george bertrand]

i have a 337b that the pump was leaking from between the housings on the pump. replaced the pump and no more leak