power pack repair

SteveG · #1 10-05-20, 05:28 PM

Hello all,

My 337A with the all hydraulic power pack has developed a fluid drip from the priority valve which vents to the exterior. Guidance from anyone with experience in remedying this problem would be greatly appreciated. Rick Cox of Cox Airparts has quoted me $2450 for an overhaul and is unwilling to repair as necessary. This seems like an awfully expensive o-ring replacement but considering the work required to r&r this unit I certainly do not wish to do it more than once. That would seem to preclude a salvage yard part of unknown condition. Anyone else attempted a field repair and how did that go? Any and all insight gratefully received.

Regards, Steve G.

cessnadriver · #2 10-05-20, 07:56 PM

Steve G. IF YOU ARE SURE IT'S LEAKING AT THE PRIORITY VALVE! I personally have NOT disassembled the power pack, but looking at the parts manual, FIG 113, Items 44-49 is the priority valve. ALTHOUGH not much room to work, you'd have to remove all the hydraulic fluid, remove the reservoir top and remove the priority valve, from the inside of the reservoir, with a socket, replace the two o-rings Items 45 and 46. Re-install the valve, fill reservoir with H-5606. Then check for leaks. Again I have NOT preformed this type maintenance but looks fairly simple.
Regards, Bill Story
'65 C337 owner/pilot/A&P

SteveG · #3 10-05-20, 08:24 PM

Hi Bill,

Thanks for the reply. But my analysis of this is less optimistic. Removing the cover and working from the top down into the bottom of the canister does not seem feasible. The service manual says to remove the unit from the aircraft, a job I conservatively estimate as being 5 hrs. of backbreaking work. And then there's the matter of setting the pop-off pressure. Apparently requiring capping outlet ports and connecting a lever pump & gauge. Both the manual and the overhaul shop suggest that once opened it is indeed a Pandora's box of cascading problems and that an overhauled unit may be the more cost effective solution in the long run. That said, I'm still considering the field repair option if anyone can report an actual success story.

JAG · #4 10-06-20, 11:53 AM

Steve,
I have not tried the field repair - but my thoughts are like Bill's; the maintenance manual has the steps to do this. Removing it sure seems like a nightmare, but once you take the seats out, drain the fluid and get up under there with some good lighting, it is not that bad.

I have built myself a hydraulic power cart with a regulator and pressure gauge that I use for swinging the gear - if you have something like that it would be fairly straight forward to use something like that to do the testing (may need a few extra hoses, etc.

If that seems like too big a job to pull off - my next step would be to take Rick up on his overhauled unit. The PowerPack is the brains of the landing gear.
Jeff

SteveG · #5 10-06-20, 09:12 PM

Hi Jeff,

Thanks for the reply. Unless I completely misunderstood Bill, I think he was suggesting pulling the valve in situ rather than removing the entire assembly but trying to work from the avionics access plate downwards doesn't seem feasible and won't allow for portable power to be connected. I have a power cart, in fact posted a picture awhile back in a different thread topic, it just seemed like using it was like using a chainsaw when a scalpel was the right tool, no finesse in measuring the pop-off pressure. The service center rebuild would be convenient but I'm usually disappointed every time I try just throwing money at a problem and 25 c-notes for some o-rings just seems excessive. When I suggested same I just got the usual blather about "well, you know, liability and all". The only reason I'm considering it is I don't much want to revisit this project site next year when the other shoe falls and I end up wishing all the seals had been replaced while it was out and open.

JAG · #6 10-07-20, 11:44 AM

Sorry Steve - when I reference Bill, I was just referring to doing it yourself - but if I was doing it, I would likely take the PowerPack out, and replace some of the other seals as well. I recently had a leak on mine and had to replace the o-ring and the backup ring on the "landing gear down" fitting on the bottom of the unit - was just old and installed improperly and finally started to leak.

Bill's suggestion of going through the top is not a bad idea if you don't have too many avionics in the way - mine has good access since I installed G5s in the panel.

I like the chainsaw analogy - ha ha. I suppose even a handpump set-up could be used. I have used this handpump in the past for engine pre-oiling. May work for this? I think you can find higher pressure ones...

https://www.amazon.com/VEVOR-Hydrost...89684056&psc=1