Gear Motor & Light

[djarrett]

Over the last of couple months when we put the gear up I don't get a light and the is visualy up and the Hyd motor is heard to continue to run. cycle and sometimes we get all indications or other times we get the same. My Maintance folks have jacked it up twice and we can't duplicate the same indications on jacks. works for a while and then on Friday we cycled 4 times and then aborted the flight and the Maint. folks are going to work on Monday. ANY SUGGESTIONS.
N268 DAVE JARRETT

[SkyKing]

Not familair with this version of the 337... in fact, never have heard of it before. Do you have a service manual for it??

SkyKing

[Kevin McDonnell]

Skyking,

This version of 337 is a 1975 T337G.

Dave,

I'm no expert but here's my 2 cents...

Normally the gear pump will continue to run until a certain pressure is achieved (I think it's 1500 PSI). If the pump runs continuously, then either you're not developing 1500 PSI - or the switch is faulty.

Using a ground mule (external pump & pressure gage), the shop can test & adjust the pressure switch so that it trips at the correct pressure. Maybe the switch is sticky (explaining the intermittent behavior) and can be cleaned up.

The up-light is a function of some micro switches that sense the gear is in the up (or down) position, one on each wheel. If these are not rigged correctly, then the gear could be up - but the light won't come on.

I'm not sure if the inability to achieve 1500 PSI will also cause the up-light to not illuminate. I don't have my service manual with me at the moment so I don’t know if there’s a connection between the two.

[Jerry De Santis]

I had similar problem on my 1975 P337G a few years back. The gear up position limit switch needed adjustment on my plane. BTW, if it is the same as my plane, the circuit breaker is a pull out type. If it occurs again, pull the limit switch out and a few seconds later push it back in. This should give green light with landing gear tucked away and stop the hydraulic pump from continous running.

Jerry
N34EC

[SkyKing]

Dave,

You should 'update' your aircraft type in the personal profile, since it appears from the tail number you've acquired the 1975 P-model from Arizona, N268 from the paving company. I wonder, did the previous owner provide you with any sqwauk list of his having this problem, or is this something new that's cropped up?

As I recall, the Cessna P337 model series Service manual (1973-1980) contains a rather detailed troubleshooting chart for the very symptoms you describe, but mine aren't handily available. Maybe someone else can jump in here with the info.

You did get the manuals for yours, right?

SkyKing

[Pete Somers]

Dave
I assume you have a P337G??

This sounds like one of the uplock switches is intermittant?
However if the HYD motor keeps running after the gear is up and locked, it looks like the power pack is not getting up to pressure to shut it off.
Are you sure the nose gear is up and locked.

Check the 28 volt on the motor, make sure there is no voltage drop from the contactor or the circuit breaker.
That is with the gear operating.

The pressure switch on the power pack are a source of problems, you best bet is to replace it, as it is a sealed switch.

The amber light is controlled by the uplock micro switches, any switch that is open will cause the amber light to go out.

Do all the gear doors close up propely, with the gear both up and down?

Let me know how you get on.

Peter

[Kevin McDonnell]

Dave,

I got a chance to read the maintenance manual this evening. From what I understand of the schematic, it looks like you cannot get an "up light” indication if the pressure switch has not tripped (it's "open" when there's 1500 PSI present). If this pressure is not sensed, then it grounds the voltage that otherwise would have illuminated the up or down lights.

Since the symptom involves the motor running continuously, I think the pressure switch is the first place to look (vs. the uplock switches). It can be disassembled, cleaned, and adjusted (with shims) to set it to trigger at the desired pressure. The bottom line is that you need to figure out if the correct pressure is being achieved and not sensed, or it’s not being achieved.

The book also points out that the gear system is very current hungry (30 amps starting & 20 amps running) and somewhat sensitive to low voltage. You may find that running it on the ground off of a healthy mule gives you good voltage, but due to dirty connections/corrosion etc., in flight the plane’s electrical system may not be providing the same voltage.

Let us know what your mechanic finds.

[djarrett]

well Here is the results from the maintance shop. we cycled it ten time before the battery got low and then things stoped working. We always got a lite and the motor would run and hit 1500 when we hooked the system to an outside guage. So we couldn't duplicate the indications on the ground. we did notice that the main gear leg squat switches were a little loose so we made sure they were set properly, and secured. Did a little test hop to see if we figure out the problem. Gear up fine and with the generates off the battery never missed a beat. Once everything stabled we droped the gear no problems, the outside gage hit 1500 and the motor shut off and cycled once and then the pressure guage hose poped a hole and blew fluid all over everything and we went home and landed uneventful. We will try again wothout the extra pressure gauge after cleaning up the inside.

DJarrett

[SkyKing]

Did you or your mechanic ever check the gear selos to make sure yours are in compliance with the Cessna service bulletin? The earlier units didn't have removable tops for cleaning the plungers and could definitely lead to a problem. They were supposed to be changed out.

SkyKing

[djarrett]

Well I think we have got everything working right at this time. we have had a total of 8 cycles in the air and we haven't had a problem. Thank you everyone for your input,

DJarrett

[SkyKing]

So... now that we've all been held in total suspense awaiting the final outcome, just what WAS the problem anyway... was it ever isolated?

SkyKing

[djarrett]

what we found. left main gear squatswitch was loose and sometimes gave indication or flickered. switch was tightened and properly positioned. the hyd pump was working properly and turning off when it reached 1500 psi and then a short cycle and turned off. When your head was lowered to attempt to hear the pump the cooling fan sounded different when you head was lower than the dash. The cost of figuring out the bugs and time and no parts, was a little over $300. the shop ate the cost for the cleaning of the cockpit and scrubing the carpet.

Thanks again

Dave Jarrett

[Learjetter]

Gang,

Ran across a neat blurb in a Cessna Pilot Assn Tech Note (#337-T02) that relates to this issue. The Tech Note advises installation of a "HYD WARN" or "HYD PACK ON" annunciator.

Here is a summary of the relevant text:

Adding a gear motor running warning light, your option

The addition of a warning light connected to the control coil circuit of the gear motor contactor can help in determining proper gear operation. This light is connected in parallel with the contactor and would be on whenever the closing coil of the contactor was energized. With the high noise levels in the cabin and the invention of noise canceling headsets, it is difficult to hear the powerpack running.

The normal gear retraction cycle takes 12 to 16 seconds and gear extension cycle 10 to 14 seconds. Timing the light on and off cycles can check these times. The normal cycling of the gear motor in flight that occurs once every 20 minutes would cause the light to come on momentarily. This event
is usually observed by the pilot as a flash of the discharge light or a negative short time duration pulse in the ammeter. The pump motor contactor can fail to close preventing power to be directed to the pump motor. The warning
light on and no gear movement would indicate this condition. A failed pump motor or open circuit breaker would give the same indication. A failure in the gear down switch circuit, a faulty switch, or broken wire, will stop the gear
system from completing the cycle. The gear will be down, the doors will not close, the green light will be off, and the pump will continue to run. In this example, the pilot would be alerted to a problem with the absence of the green light and the warning light staying on past the normal 10 to 14
seconds. Pulling the 30-amp breaker can shut off the pump motor and a landing with the doors open can be made. A little troubleshooting and repair and gear function should be normal again. This light is not a cure all but can help in determining the difference between a problem or just normal operation.

The part number for the light is MS 25041-4; this is the same light as the amber gear up light installed in the aircraft now. It is available from Aircraft Spruce & Specialty Co. www.aircraft-spruce.com (800-824-1930), (877-477-7823), (fax 714-870-7551), and sells for about $26 ($45 in 2021).

The bulb is the standard GE-327 lamp used for all the post lights. This light has the press-to-test feature so it can be checked any time to be sure the lamp is not burned out. The light should be installed where it can be seen easily and not buried down by the powerpack in the lower quadrant. A
placard with the lettering, HYD WARN, or some other similar worded statement should work. The wire size should be 20 gage, which is the same as all the other indicator light circuits, and connections made as per AC 43.13-1A. Pin 2 on the light connects to the small closing coil terminal on
the power pack contactor, and pin 3 on the light connects to the gear indicator 5-amp circuit breaker for the test circuit. Pin 1 of the light connects to a good ground point. The current draw of the lamp is .04 amperes, which has no effect on the charging system total load. This installation would
be considered a minor alteration and weight and balance change negligible. An entry in the aircraft logbooks by an appropriately rated mechanic would return the aircraft to service. Check with your mechanic to get his feeling on the light installation.

We installed a blue annunciator light in my aircraft just under the cowl flap switches and left of the gear down light. Works as advertised.

[kbecker]

I had this HYD WARN light installed a couple of years ago. I have a copy of the 337 form we filed with the FAA if anyone would like a copy. It works as advertised. 1977G

Kevin