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  #1  
Unread 07-19-09, 02:54 PM
Hank Hank is offline
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Gear problem

On my 1965 Skymaster raising the gear, normally the gear up light comes on, then the gear doors close, then the gear handle goes back to neutral. Lately however the gear up light comes on briefly then goes out and the doors stay open. Bringing the gear down and up again cures the problem, though sometimes it takes 3 tries. The doors close normally every time on the gear down cycle. Any leads I can give my A&P would be appreciated.
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  #2  
Unread 07-19-09, 04:36 PM
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skymstr02 skymstr02 is offline
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Sounds like you have an up lock switch that is losing its contact when the gear settles into the up locks, or a wire going to the switch is deteriorated.
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  #3  
Unread 07-19-09, 05:14 PM
Hank Hank is offline
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Thanks. I have visually checked the main gear uplocks and all appears fine, the nose gear uplock is under an inspection panel that only be opened when the plane is on jacks. Can the switches be tested when the plane is on the ground or does the plane need to be on jacks? And to add to the confusion sometimes the gear works normally on the first try.
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  #4  
Unread 07-19-09, 05:46 PM
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The panel on the belly behind the nose gear can be opened without the plane on jacks. Take the two tie rods from the aft door to the NLG loose, and swing the door towards the gear. This will expose the row of screws on the leading edge of the panel.
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  #5  
Unread 07-20-09, 08:43 AM
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WebMaster WebMaster is offline
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Would anyone be willing to take some pictures of the various limit switches, up locks, and adjustment points??
Since the landing gear is always an issue, I would gladly make up a web page for gear issues.
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  #6  
Unread 07-22-09, 02:38 PM
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Skymaster337B Skymaster337B is offline
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Switches are the usual suspects. However, I always start with the basics. Is the hydraulic fluid full? Since the gear seems to work after trying it 2 or 3 times it might be low of fluid...because the pressure has to be build-up to complete the uplock sequence even after the limit switches have made contact. The other possibility is air in the system too, and since it is a "self bleeding" system after 2 or 3 cycles any air will "bled" out thus allowing pressure to build up on the 2nd or 3rd try.
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  #7  
Unread 07-23-09, 07:41 AM
Hank Hank is offline
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The level was checked and a little low. After filling with fluid the gear did the same thing on the up cycle - the gear would go up, light comes on, doors close but before the handle would go back to neutral the light goes out and the doors open. However on the next flight the gear operated normally. Tom Carr at CPA suggested a broken wire in the uplock circuit. So today the plane goes on jacks and the wires in the uplock circuit are flexed to see if any cause the light to go out and the uplock switches are tested. He said any break or loss of contact in that circuit would case the doors to open.
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  #8  
Unread 07-23-09, 10:55 AM
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I am somewhat reluctant to mention this as there are a lot of A&P's here that probably know better, but I will merely advise what has worked for my like gear problems in the past.
a) Open the doors
b) Wipe all the switches off with a clean rag
c) Spray the switches with a degreasing compound
d) Blow air on the switches with an air compressor.
e) Wipe them off again
f) Spray them with WD40.



My experience has been that the switches are so sensitive that a bit of oil, grease, sand etc... has a tendancy to make them finicky. Keep them clean and lubricated, and it will potentially help with their operation.
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  #9  
Unread 07-23-09, 12:00 PM
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Skymaster337B Skymaster337B is offline
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WD-40 will fix anything! I use it by the gallon.
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  #10  
Unread 07-23-09, 12:58 PM
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1. Make sure Nose strut is serviced to specs. A models=35psi. 5606 @ correct level.
2. Check up limit switches( page 205 Serv. Manual ebook)- These can split/expand along case joint when in compression. (They look perfect and check fine when static but when compressed will split enough to become a fault.)

Sometimes the Nose strut will not make the up limit switch when not serviced properly. If you fly the plane off at T/O with minimal pitch intially the nose strut sometimes will not extend to the extension limit with non spec charge. The Nose strut fights the aerodynamic load when placed up. If it isn't correct this can cause a few problems.
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  #11  
Unread 07-25-09, 06:18 AM
billsheila billsheila is offline
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Similar Issue on my 65!

I had a very similar issue on my 1965 and spoke about it already on this forum and on the CPA website where Tom Carr was most helpful in getting to the bottom of it. In my case it turned out to indeed be adjustment of the main gear switches, as was already suggested in this thread. The issue would arise in flight but not on jacks, making it that much harder for my A&P to diagnose. As I recall him explaining it, there is a certain amount of play in the main gear when they are in the lock saddles and when system pressure and wind would fluctuate, we were getting intermittent contact in one of the main switches. It would make contact properly when first actuated, also make contact properly when relaxed in the saddle, but if you pushed up hard on the gear leg (when up and locked and on jacks) it would lose contact. Once the gear were up and locked in the saddles if this would happen the only thing would happen is that the door solenoid would de-energize sending fluid from the pack to the door circuit, opening the doors. The switch needs to be adjusted on its bracket such that it maintains contact when first actuated, when relaxed in the saddle and finally when pushed upward as hard as you can by hand (to simulate wind and system pressure changes). Not sure if this is your issue, but it certainly was in my case.

I also totally agree with the suggestion in this thread to keep the whole affair clean and properly lubed. The other suggestion (which my A&P did throughout my process was to solder the crimped wire connections on the switch wires). I am not sure if this is standard good A&P practice or what but my wires had at some point had new terminals put on, but they were not soldered and my A&P said that with something as critical as gear (and where vibration and the elements can get at the terminal) he solders the crimp.

I had exactly your issue where it was intermittent at first, and if I cycled the gear it would usually correct itself, but it got worse with time and I got it corrected at annual.
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  #12  
Unread 08-25-09, 12:47 PM
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Bill,

I have this problem chronically when the aircraft sits for a while with a low (not full) hydraulic quantity. It’s always on the first retraction cycle after a few days of sitting. I have a pair of gear door actuators that weep a little while they sit. I believe this is causing the system to lose its prime. When the gear is cycled up there are certain positions on the sequencing valve that will time out if there’s not enough pressure. I believe this is what’s happening in my case and resetting the selector resets the timer and allows the pumps to finish priming the system and complete the cycle. This annual I plan to rebuild the actuators, but in the mean time the key is to top off the hyd quantity periodically. Also with my system I don’t need to cycle the gear, just take the gear lever to the idle position for a five count then back to the up position and the cycle will complete!

_travis
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  #13  
Unread 12-23-14, 11:09 PM
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Skymaster337B Skymaster337B is offline
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Gear issue solved

I've been having the same problem, gear goes up, no amber light, gear doors stay open in the air. But everything works ok when jacked up in the hangar. I put new switches on the up locks and power pack, checked tire pressure, checked fluid levels, and serviced nose gear strut; but still nothing worked.

I finally put new springs on the main gear uplock pushrods, and I'm happy to report all is good. However, good luck finding a new spring. It seems Cessna doesn't make them anymore, and I got the last one in the system.

There's plenty of used springs available, but good luck using them since you already have a used one installed. The new spring was a full 1.5" longer than the old worn out one.

Enjoy,

Rob
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  #14  
Unread 12-26-14, 12:00 PM
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hharney hharney is offline
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The new spring is longer? Does that make sense, wouldn't the old one be weak and stretched?
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Herb R Harney
1968 337C

Flying the same Skymaster for 47 years
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  #15  
Unread 12-27-14, 10:57 PM
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Skymaster337B Skymaster337B is offline
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The old spring is shorter because it was under constant compression for the last 40 years.
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