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Landing Gear Problem Solved -- finally!


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Electric landing gear would always extend normally but intermittently would not retract.  Troubleshooting confirmed motor needed overhauling (bump motor with fist when in failed mode or reverse leads and it started immediately).  Overhaul shop found brushes were completely gone.  Overhauled motor was reinstalled in plane.  Same problem.  Diagnosis found motor was again not working properly (same symptoms).  Motor was returned to shop where a new armature and another set of new brushes were installed.  Reinstalled motor in plane.  Same problem, but troubleshooting confirmed motor was now working normally.  But now when the DN relay was tapped lightly the motor started immediately.  New down relay was installed.  Same problem. Tapping the DN relay did not start the motor now but tapping the UP relay did!  UP relay was also replaced.  SUCCESS!!

Moral of the story... if your Mooney has over 3,500 hours and/or is over 40 years old, you probably should have the gear motor overhauled.  There is a 200-hour requirement to inspect the gears and coupler in a Dukes actuator, but the brushes (inspection not required) cannot be inspected without destroying the caps (which are epoxied in), so they need replacing anyway in order to inspect them.  The motor overhaul was under $1,000.  You might also consider replacing (or cleaning if you’re lucky enough to have Cutler-Hammer relays) the gear relays since they have had a good life and can start causing real problems when they get weak.  If one relay is bad, chances are that the other one is not far behind.

This happened in a '77 M20J with 4300 TT that has a Dukes 1057 gear motor with 40:1 gears but could happen in almost any Mooney.  I don’t want to hear from you guys with Johnson bars though!

Hope this saves someone the headaches and expense I had wrestling with this compound problem that was defying resolution.

-Lee

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I've found that you can get the epoxy off of the brush caps with dental picks. If you get under it with a chisel point you can pop it off. After inspecting the brushes I seal them back with tank sealant. It holds the brush caps on better and is easier to remove.

I had the gear fail once and had to use the crank because the epoxy failed and the brush cap vibrated off.

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  • 3 years later...

I had the same issue with our 1977 M20J and the Dukes 1057 actuator. It is very easy to shatter those old brush holders due to the epoxy on the caps. So folks are not pulling the brushes for inspection and they will eventually wear away completely, causing this:

IMG_2638.thumb.jpeg.820e5d385d29ea1381647c56d6efba50.jpeg

Luckily I was able to crank the gear down and land OK.

After a LOT of research I was able to track down the original brush holder and brush manufacturers and had new engineering drawings created for these parts.

414766680_ScreenShot2022-01-07at9_33_22AM.png.aaa30b49098d2e08ed810635b4d561df.png

There are minimum order quantities and so I went ahead and ordered to get N201JX back in the air. Kind of expensive but......

For 1977 M20J owners with serial numbers below 377, this may be interesting. The brushes, bearings, and wire necessary for the rebuild are all "standard parts" and would require no PMA or STC. The brush holders and caps are another story, for me personally they were "owner produced parts" and a "minor modification" (e.g. the method of safetying the brush caps). However, to have some of these parts available for others will require consultation with my local FAA MIDO.

The threaded caps can be sealed on with tank sealant as others have suggested, but safety wiring the caps may be a better idea. That is still in work, as I said below. With the safety wire it will be very easy to inspect the brushes as an added part of the normal 200 hour inspection called out in the Mooney M20J Service Manual 5-20-06, Section 3, paragraph L:

877086471_ScreenShot2022-01-07at9_20_29AM.png.bf6cc4601a687c95a09317a0f0a506b4.png

I would add:

Inspect the gear actuator motor by removing the brush caps from the brush holders, remove and inspect the brushes. If the brushes are worn to a length of .25" or less (33% of original), replace the brushes.

Now, that .25" (33%) is subject to review, I was balancing remaining wear versus spring tension in suggesting the criterion. Comments and suggestions welcome.

Inspection and servicing of the gear motor bearings and commutator for the gear motor is not specifically addressed in the SM, but this level of work is outlined regarding the starter motor. So it should be doable by any A&P.

LASAR used to send their Dukes gear motors to George's Electric in Sacramento for rebuild but he is closed down. Our 40:1 Dukes gears are still in great shape (proper maintenance, yay!) but replacing the unit with the $8500+ ITT actuator (if you can get it) versus rebuilding the electric motor and setting it up for continued easy inspection and service is kind of a no brainer.

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  • 3 months later...

Hi all,

Long time lurker. Finally decided to join. I had this problem a couple of days ago. I couldn't get the gear down and had to bring it down manually. It's funny because when I bought my Mooney, that was my biggest fear - being alone and not having the gear extend. I will say, however, that it wasn't really a big deal to extend the gear mechanically. It was a bit strange to land with the fire brigade standing by next to the runway. Apparently the problem was - as you have pointed out - the actuator motor and associated brushes / brush caps. FYI, my Mooney is a 1977 with 3700 hours.

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  • 3 weeks later...

So.... My mechanic tried to replicate my problem. Gear up - check. Gear down - check. He then cycled the gear up and left the plane for 1-1.5 hours. Gear down - problem. Then they removed the motor and sent it to a specialist. Some things were found, but when they tested the motor, it worked. There is nothing wrong with the electrical system/relays. Now they're telling me that they can't find a problem to fix and they can't put the motor back in without fixing it. They recommend to replace it, but can't find a replacement.

Any thoughts from you guys?

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Do keep in mind Sue is on Swiss reg, so the usual N-reg ways won't work.

Sue, to be honest, I would look for a mechanic / shop that is more reasonable. You can do A LOT of stuff the FAA way on privately owned planes under EASA. If you are at a loss, perhaps try talking to Malte Holtken from https://aufwind.aero/ - he works with EASA on things like CS-STAN. You also might want to join EuroGA and look around there.

Whatever you do, don't let your current shop put anything in any logbook.

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4 hours ago, Sue Bon said:

So.... My mechanic tried to replicate my problem. Gear up - check. Gear down - check. He then cycled the gear up and left the plane for 1-1.5 hours. Gear down - problem. Then they removed the motor and sent it to a specialist. Some things were found, but when they tested the motor, it worked. There is nothing wrong with the electrical system/relays. Now they're telling me that they can't find a problem to fix and they can't put the motor back in without fixing it. They recommend to replace it, but can't find a replacement.

Any thoughts from you guys?

Did they check the brushes? As the brushes wear they can hang up in the holder causing a failure, as the gear motor gets bumped around while removing/handling the brushes free up and the motor starts working again 

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Lubing the relays seems to have a similar effect when they get dirty.  “Exercise” them a few times and a little lps 1 and suddenly they are fixed, but we didn’t do anything??? We’d likely be able to enter the logbooks with “ lubed gear relays, lubed landing gear 40:1 gears, ops checked gear, all systems working normally, airplane is airworthy…”. 

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  • 1 month later...

Update: I finally got my "Old Girl" back today. The actuator and motor were sent to LASAR and the problem was indeed, the brushes. I got some explanations, but they were in different languages and so I didn't really understand it. I don't even understand it in English, but I did understand "brushes" and "inconsistent contact."

Did one Touch 'n Go and one full stop and everything worked perfectly, except the pilot who was very rusty after two months on the ground :wacko:

 

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