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Landing gear Motors and Transmissions.

landing-gear related Service Letters and Bulletins

SL-447 - Inspection of Landing Gear Transmission Retract Spring; all models.

SL-650 - Inspection of Landing Gear Retraction and Flap Control Transmission Assemblies. Read this, there is a mention here about defective Dukes transmissions on page 2.

If you want me to service your landing gear transmission and/or landing gear motor, contact me for details. See the overview below.

Click here for a brief overview of the process for servicing a Dukes type landing gear transmission.

I currently have 2 Dukes transmissions for sale on an exchange-only basis. These belong to an "investor". I didn't set the $3995 price; I just make them pretty and servicable, and ready for sale.

Above is a typical Dukes transmission assembly complete with motor and brake asm.

you probably already know how rare this item has become.

Here is the Dukes #4 lubricant called out in the Comanche special service instructions. It is a 2-ounce tube, adequate for 3 transmission services. FYI - Dukes instituted a minimum purchase per invoice of $475 back in 2010 which is why I previously stocked this grease. Their new policy excludes this service item so you can now purchase it directly from Dukes; here is the phone number (818) 998-9811. BTW their new price is $91 per 2-oz.


If you're interested in making your own "Dukes" type grease, here is how to proceed. Referencing the Mooney bulletin I have made these simple instructions for you to print.

Landing Gear Motors.

There are 2 slightly different American Bosch motor styles used in the landing gear system. The difference - one has a cast end housing and one a stamped end housing. The motors are interchangeable, however some internal components are not.

MO72218A disassembled
1711920M027MM [OHC]
Cast-type end housing American Bosch motor; click on the photo for a look at a ready-to-assemble motor.
Stamped-type end housing American Bosch motor; click on the photo for a look at a "finished" motor and brake coil.

Click on the photos for further details; here is a video/audio of a running motor [without legs!] on the bench.

I stock landing gear motors which have been remanufactured by an FAA repair station; they have the 8130 forms. For you overseas customers this seems to be the "cleanest" approach to your dcumentation problem. Since there is no mention of servicing these motors in the Piper Comanche service manuals we are either to ignore any un-approved service or bite the bullet and pay the fiddler.

Transmission types.

There is one basic Piper part number covering the two manufacturers; they are interchangeable.

A suggestion for easy determination of which transmission manufacturer you have installed; click on each photo below, print them and take to your airplane for comparison.

Dura Transmission
Dukes Transmission
Dura Transmission - most common type
Dukes Transmission - more durable type

The above photos show you how to identify the differences between the manufacturers; there are a few ways besides the above illustrations. The Dukes uses 6 countersunk screws holding the end plate to the housing; the Dura uses 5 non-countersunk 10-32 screws. The Dura must have the bearing retainer; the Dukes design does not require that band-aid. The Dura has 4 holes, 2 used for the motor mounting; the Dukes uses either a slotted design [above] or one with 2 holes, one hole per leg [below]. The Dukes photo above shows the slotted design. So there you have it again, more information than you really wanted to know.

click to enlarge
click to enlarge

Dukes with 1 hole per leg - note hole offset aft of centerline

Illustrating "clock" position of mounting plate

Contact me with any questions about availability or servicing these transmissions.

When we're out of landing gear transmissions; we're out of Comanches!

BUT WAIT! I have finally completed the prototype "dukes" replacement transmission, a 7-year battle. I'll post a picture when I figure out how; this newer version of the web disigner has me baffled.

Comic relief - we may all need some of this

Notes and repair information.

The Dukes transmission [without motor, brake, and release arm] can be overhauled at Dukes, Inc for approximately $3,200 which is the latest quote I have from them; I no longer keep a Dukes overhaul on the shelf for exchange. However I do have exchange Dukes units available [not Dukes, Inc OH]. See the parts for sale page. If you choose the Dukes Inc repair, your transmission will be returned overhauled but they [Dukes] do not consider cosmetic improvement of the tube and release lever a part of their service, because they supplied the transmission to Piper without that component. I have the tube and release lever done separately; you may likewise.

Dukes, Inc says that they have never released a repair or maintenance manual for these transmissions. They continue to say, therefore how can anyone else claim a repair on an 8130 referencing what manual? So if this is accurate information, then the only approved repair facility for the Dukes transmissions is Dukes, Inc. I could be wrong on this opinion.

And if you aren't bored enough just yet, there is a note in the Single Comanche Parts Catalog concerning the Dukes transmissions. It seems there was a bad run of actuator screw from serial number 919 through 1068 [see SL-650 above]. If you have one in that serial range you must replace it immediately.

If your Dura transmission has a loose bearing, you are probably out of luck. I usually have a Dura on the shelf for exchange. I am not aware of any facility holding an approved process to repair this problem except the facility in Michigan who charges about $3,300; some may be on the horizon. Again if your Dura has a bearing retention problem you had best find a Dukes to replace it before the supply dries up. The Dukes transmissions were demanding $2,250 in used condition, no motor. From there you'll have to do an inspection and if the gears are bad, add another $3,200 to get it repaired at Dukes.

More recently these transmissions [without release arm and motor] are fetching nearer to $3,000 on the tail of the statement that Dukes quoted me $8,000 for new PMA transmissions.


Next comes the discussion of greases and which to use inside the transmissions. The Dukes transmission and its specified grease is a no-brainer but what about the MIL-G-23827 [Aeroshell 7] specified for the Dura? The manuals say "no substitution is allowed in either transmission". Gear wear is the issue [from lack of service specified annually or 500 hours; or inadequate grease spec - Dura; or normal wear - things do wear out you know]. there are better greases available than the #7 for this application. My point is, use the Dukes grease in the Dura also. If you don't have that grease at least use the Aeroshell 33MS which may be somewhat easier to get your hands on in short notice. See above "ALTERNATE GREASE" discussion.

Read this about Aeroshell 33MS which is a 5% molybdenum disulfide additive [Dukes is min 10%]. i would recommend this grease in your Dura transmission if the Dukes grease is unavailable [get some, the grease is cheaper than the gears!]. FWIW the Lubriplate® MoLith #2 is 2% molybdenum disulfide.

Don't tell anyone but I use the MoS2 grease on the actuator screw also.

Dukes grease as specified in the Service Manuals. There are 2 Dukes greases found in the Single and Twin SMs; I asked Dukes about this - they are the same specification grease. I no longer stock the Dukes grease.

Transmission service as specified in the Service Manuals. This applies likewise to the flap transmissions; wouldn't that figure? I'll wager the flap transmission service is the 2-nd most-ignored service in all of Comanche-world.

Here's my bet on the 1st place for most-ignored. If you search the SMs you'll find a note requiring 2000 hour or 7 year repetitive inspections of the airframe requiring headliner removal and upholstery panels. Aren't you happy to know that? I know, "quit reading"!

The brake coil assembly; reference Piper's P/N 23042-000 & 24948-000. A note concerning the brake coil mounting plate; if transferred from a Dura to a Dukes it may need a little attention. I can provide this component "owner produced".

Transmission problems.

A normal transmission makes an even noise like a, well - a normal landing gear transmission noise; how else would you describe such a unique sound? Listen to the audio of a cycle procedure. The purpose here is to demonstrate there are no abnormal noises.

This next lengthy audio [load time may be > 1 minute unless you have a really fast system and high-speed internet connection] demonstrates a retraction and extension procedure. It's purpose is manifold. 1) - you can hear the changing sound at the end of the retraction cycle when the main gear legs contact the gear bumpers snuggly. 2) - the video also shows an ammeter in the system, while the voice is reporting the voltage.

Worn actuator screw [aka jack screw] and nut. If there are pits in the grooves of either component this will make a noise sounding like a rock crusher, a garbage disposal, or a thrashing machine depending on what area of the country you are from. See the 100-hour lubrication requirement; failure to perform this can lead to failure of the actuator screw and nut. Here is a photo of a pitted actuator screw; this will be very expensive to have repaired. A possible cause - Balls that are severely worn or damaged? Again, probably lack of adherence to the service recommendations.

Worn gear; the mating gear is not too pretty either. This condition may not be detectable except during the 500-hour or annual inspection and lubrication requirements specified in the Service Manuals. The gears in these photos are from a Dukes transmission that had no reported abnormal noises.

End play in the actuator screw where it enters the transmission housing casting. This video also shows the early style brake assembly which should be replaced with the later "plunger" style brake coil. See "brake coil" above.

There is a Checking Procedure in the Service Manuals for this loose bearing; also see the "Various Videos" link where you will find 3 videos of this condition. This is partially due to the weak design of the Dura type transmission. The offending bearing is swaged into the casting; Piper added a bearing retainer to prevent catastrophic failure after serial number 24-735, and provided a kit to retrofit serial numbers 1-735. This bearing being pulled out of the casting can be aggravated by excess friction in the push / pull cables [conduits] and improper down-lock micro switch adjustments - too close to the end of travel. Read this switch adjustment procedure, it's better than the vague SM description. Piper also issued a SL-315 covering this transmission problem. This Piper publication is several pages long, covers quite a breadth of issues, unfortunately however contains errors. I'm working on a corrected version but it isn't top priority. I'll post it when available.

The Dukes type transmission is a more durable [sic] unit not suffering from this loose-bearing syndrome.

Resetting the landing gear transmission after a manual extension procedure - A really easy method and explanation.

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