Help...Gear Won't Come Up - Page 2

GMAs · #16 10-01-02, 10:17 PM

Well you just spured my funny bone.. and I got up and went and got the service manual... sure enough the old grey matter hasn't gone south yet... ahhhh the battery switch turns on the master... the master is connected to the battery... and then thru the contactor to the two starter contactors thru them to the starter.....

Now on one side their is this big piece of copper strap... that ties the two starter contactors togeather.. and attached at one of them is the cable that comes from the master contactor...

Page 6.1.0 shows the wireing diagram of the starters system and pp 4.1 Battery circuit shows the bat contactor...

Now it might be wired different on yours... but, I am going with the factory wiring in the book... and what I have seen on the planes... smile...

I am sure you mean the copper strap.. that goes between the two starter contactors... thinking that it comes from the battery at that point... ahhh well I guess I should go snap a picture eles if you have one.. to show.. would end the cold fussion... smile...

ya the contactors are good for about 5 years.. or less and in the tropics I am sure they go out even more often... their just isn't anything better out their yet... they haven't come across with a 400 amp high surg transistor yet that can take its place.. smile.. when they do.. change smile...

the gear pump is rated for 60 amps surge and 35 run... so one alternator will do the run.. but, yes the two of them have to be on line to make a good start of things... or else the battery has to be their too... I agree.. but, it will run on one alternator...
G.M>GMAs...

Bob Cook · #17 10-01-02, 10:45 PM

GMAS

Apparenty mine is wired differently. the current shunt is in series with the battery and goes the the Master solenoid. the other shunts (2) are in series with the alternators. The master solenoid coil goes to a fuse on the firewall then thru a switch to the battery.

There are small parrellel cables connecting the 3 solenoids (no copper straps). I know for a fact the starter current DOES NOT go thru the master solenoid. The coils are energized thru the master.

I was planning on putting a lamp on each starter solenoid so that it would be lit when the solenoid was energized in the event the starter solenoid stuck closed which could cause either a fire or a burned out starter. I remember distinctly that there was no real way of disconnecting the starter solenoid in the event the contactor "welded" together.

In fact this has happened on occasion with other owners.

either the P is different or my aircraft is different.

FYI

Bob

Dale Campbell · #18 10-02-02, 02:42 PM

My 337H has 2 little amber lights at top of panel, 1 for each starter contactor. If either stay energized the light stays on. I do not know if it was there from factory or added later.

Ernie Martin · #19 10-02-02, 04:51 PM

We’ve run some of the diagnostics tests suggested (couldn’t do more because my A&P is busy on something else).

1. Gear doors were opened with the hand pump, the master was then turned on and the doors closed swiftly in 1 or 2 seconds. Powerpack performance seemed perfectly normal.

2. Nose gear was jacked up, the oleo came out smoothly and the squat switch clicked to the “closed” position. We didn’t actually confirm a closed circuit, but the switch clicked each time the test was repeated.

3. Voltages were measured as GMAs suggested and all was found normal. Specifically, there was negligible voltage drop across the master solenoid. (Also, it seemed from the wiring that current to the starter solenoids flows first through the master solenoid; since both engines are starting normally, that suggests that the master solenoid is OK.)

4. While not strictly a test, an IA who was with us when we were discussing the problem said that it sounded to him like an OVERVOLTAGE – not undervoltage – condition. He says the alternators may have dropped off, not because of excessive load current (which would have tripped the breaker), but because of an overvoltage. I seem to remember that the overvoltage light went on, but I can't be sure. Any thoughts?

Since I’m sure that in-flight not even the doors opened, seeing the powerpack work flawlessly in test 1 suggests to me that it may not be the powerpack. I’d like to continue diagnosing this, but my A&P is unable to get to my plane full time until Friday of next week, when he’s planning some retraction tests with the plane jacked up. He has, however, an hour here and an hour there. Are there simpler tests that we can do on the ramp to further diagnose this? I’d like to do the test suggested by Skyking (and I think also by GMAs and by Skymaster?) of jacking only the nose gear (to activate the squat switch) and try to raise the gear with the powerpack while the mains are on the ground, turning the master switch off as soon as the doors open and the nose gear starts to move. But I’m a little concerned of doing damage to the airplane and I want to get clear procedures on resetting everything back to normal-gear-down status. Is this safe? I take it that Skyking, GMAs and Skymaster have done this before? Any further thoughts on this – or on other tests – would be very welcome.

Thanks,
Ernie

stackj · #20 10-02-02, 10:20 PM

After rebuilding the nose strut on our 1967 skymaster I had the idea of testing the retraction mechanism by doing just that. I only used the hand pump as my hydraulic pumps are engine driven. I called the Cessna service center and talked to Cliff Ives and asked if this would be a safe way to check the nosgear for proper retraction. He supported it fully and when I tried it, everything worked fine.

I'd be very cautious when running the retract test with the ELECTRIC pump. Make sure you shut it off as soon as the nosegear starts to retract (Use the master switch). I don't really think the electric pump would be able to fold the main gear with the aircraft weight on them, but I'd certainly hate to be the one to test that theory.

I wouldn't think there would be any problem letting the electric pump extend the gear.

GMAs · #21 10-02-02, 10:35 PM

Naw... look for the extra few min of jacking the plane up... I would rather get it all the way up.. and let the gear swing... if you put it up on the ground.. you are putting a huge strain on the actuators as they will try and make the gear come up.. and can't because of the over center part... but, it will put a lot of load on the gears and hydralic stuff... not good... I would think trading one problem for another is not what I want to do... so I would just as soon jack her all the way up... heck it only takes 15 min... and then you can cycle the gear and give the pump motor a good work out... because I think you will find it has a bad segment in it... from what you have said...

sounds like the rest of the system is working but, I would also go do a contenuity check on the squat switch... too.. just to be sure.. clicking the switch is one thing.. making contact is another... and then also I would pay close attention the the wires going to the switch... as they could have a intermitent thing also...

got to be one or the other of them two.. and I would hope the switch but, from the indications you mentiond the first time... I put my money on the pump motor being bad... we have seen a couple of them now go south strangly... and it sounds like yours is headed that way too...

As to the overvoltage... ya it would trip the alternators out.. but, so would a spike and then a surge... G.M. GMAs...

SkyKing · #22 10-03-02, 03:58 AM

Ernie,

You won't have any problem jacking the nose and working the nose gear with the pump... just pull the breaker before the nose gear completely retracts. The hydraulic pressure isn't going to get switched to the mains until the nose gear is all the way up. Once you've pulled the breaker on it, then you can freely move the nose gear up into the wheel well all the way if you like by hand. When you're ready to put it back down, move the gear handle to the down position and then push the breaker in. Pretty simple, but as GMAs says, you don't want to be putting a strain on the motor/pump, so just don't let it go all the way... when it kicks up, and it will happen pretty fast... pull the breaker.

Hope this helps... BTW, we've done this a few times and you're not going to break anything... but DO make sure the jackpoint is secure on the jack... and make sure the nose wheel is off the floor... you don't want the nose gear kicking up and causing the airplane to 'roll' and cause it to fall off the jack. Just be cautious and careful. And block the mains so in case the nosewheel isn't off the ground it won't cause the plane to move.

SkyKing

Dale Campbell · #23 10-03-02, 09:32 AM

I agree with all GMAS & the other say with the precautions. The best way to really test things is on the jacks. Use the power pack to move the gear because I also think the power pack motor is your problem. As far as doing damage to system, remember the system turns off when the pressure reaches 1400 PSI with the switch on top of pump. Thats what hold pressure on gear when gear is all the way up or down, even though the locks are in. I to have had a lot of problem with gear, both going up & down.

Guy Paris · #24 10-03-02, 09:39 AM

Ernie, I would personally wait and have her jacked up totally. Why chance anything of this nature. Its scary enough seeing her fully jacked as it is. My last annual I had the main gear actuators removed and gone thru, new O rings etc. the size of them to me looked like they could lift a small dump truck.... Remember Murphy's law.... My .02 cents worth. Guy....old72driver....

Mark Hislop · #25 10-03-02, 10:34 AM

Ernie:

In your earlier posts, you mentioned several times that the "red undervoltage light" came on. In my 73 model, the red light is an indication of over voltage. The over voltage circuit then trips out the alternators. Perhaps your IA is on the right track.

Mark

Ernie Martin · #26 10-16-02, 08:14 PM

For those of you who followed this thread, we’ve found the problem and it may surprise you. To remind you, the gear failed to retract on my 1973 337G after take-off and both alternators tripped off. Several tries failed the same way. Notice that none of the gear-retraction elements occurred (doors didn’t even open) and that the circuit breaker never popped.

After tests showed that the squat switch was OK and that if you manually pumped the doors open the hydraulic powerpack would close them promptly after the master switch was turned on, some people (principally Bob Cook) suggested it was an electrical problem, not a gear problem. The master solenoid switch, the alternators, the battery and all connections (including ground) became suspect.

OK, ready? It was a bone-dry battery. Filled it with distilled water and charged it, and everything is working fine now. I, of course, will take the heat for not being on top of this the way I should, but I thought you’d be interested. Couple of lessons here (aside from the importance of doing routine maintenance). First, the airplane is a system, and if one element is out of whack, some of the other elements may not work satisfactorily. Second, look for the obvious and simple stuff first. Don’t go off sending the powerpack to be overhauled.

Ernie

GMAs · #27 10-16-02, 08:49 PM

I thought you said that you checked the battery... before we started this exercise... and said it was good... Well no reason to put water in now.. that one has probably already starte to sulfide out... if it is dry... means that the resistance inside is shot... and thus boils the water because of cells starting to short... its is a sign that the battery is going.. need to do a load voltage test to be sure... the old way was with a hydromiter...

So no reason to service it now... once dry.. throw it away.. and get a new one... adding water will only strand you someplace.... if it doesn't test out...

Mantance huh... how long you owned this plane... battery water is supposed to be checked every ... how many hours... what else hasn't been checked on this bird... that should be... ernie...

they print a neat little chart in the front of the service manual and in the POH for frequency of service to what part... and surprise.. its part of the pilot responsibility... thing... that is supposed to be done before flight... according to the FAR's... your plane was not serviced and as such was not in contenued airworthyness... shame shame on you ernie...

Ok ernie... turn in your secret decoder wings... glad you found the problem ... smile... poor old alternators... were working their little shafts off... smile... good thing the regulators worked... and tripped out... else you would have been buying a lot more than a battery... by the way when you put the new battery in.. you want to check the alternators out too... for voltage level.. as they might be just a little hot... and the other reason for the battery being boiling... smile.. Nope... I don't think your out of the woods yet... ernie... you got more problems... because the alternators should have stayed with you and made the gear motor work... even with just a smiggin of a battery... G.M> GMAs

tropical · #28 08-13-09, 07:31 PM

Quote:

Originally Posted by SkyKing

Does yours have the later solenoids -- as recommended by Cessna for changeout --that have the removable tops so the plungers can be cleaned?

My door solenoid is sticking on my 74 G and I have the new style. How do you go about cleaning this?

tropical · #29 08-28-09, 04:39 PM

OK, nevermind, I found it in the MM Chapter 5-171H.

JERRY KAONO · #30 11-02-09, 03:33 AM

I have a 74 337G non turbo, during annual and in inspection and gear actuating cycle, I had a similar problem that for months I grappled with everything from the power pack to electrical, to mechanical and isolating micro switches. I was baffled, read, read and read some more.
I inspected other skymasters on the field and couldn't for the life of me figure out what was going on. The Schematic was tattooed on the back of my eyelids. weeks later I was laying on my back, stairing into back of the pedestal, all but ready to cry when the back of my hand happened to touch against the power pack gear down solenoid !

It was hot and every time I cycled the gear switch the doors would open, gear would just hang up in the wheel wells.

I cut the safety wire, disconnected the wires and unscrewed the solenoid. I bench checked the solenoid on 24 volts, it would get hot. I took a needle nose reached in and pulled the needle bearing like piston. It was discolored brown, not rusty but very sticky. I cleaned it up in solvent, wiped it off, lubricated it and put it back inside the solenoid and applied 24 volts again, this time it remained cool! HOWEVER.....

The piston shot out clear across 50 feet and hit the hangar wall like a bullet! I spent a week looking for that plunger. A long story short........ I cleaned up the other solenoid, installed and doors and gear open, come down, close, doors open, retract and doors close. Not another problem since.....