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Gar-Kenyon shimmy damper Servicing

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sierrakilo99

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I'm posting this to assist someone in the future who may need this... you CAN service this unit.

I'm rebuilding the nose gear on my Arrow and one of the items that needed attention was the circa 1980's shimmy damper made by Gar-Kenyon. Reviewing the service manual Piper states:

"The shimmy dampener requires no service other than routine inspection.
In case of damage or malfunction, ~ dampener should be replaced rather than
repaired."

Well, looking around there are options for replacements available:
1 - used on ebay for about $300 and not working correctly, or who knows what condition... same result
2 - used, and 'serviceable' for $1200 from one of the salvage yards... ouch... that's expensive!
3 - new, for $3200 from Boeing/Aviall - not going there...

So mine (Gar-Kenyon p/n PS50152-3) was leaking at the shaft end, and after looking at my (expensive) options, I opted to attempt to service... having done a few repairs to hydraulic units like this one, I figured, how hard could it be? It couldn't be that difficult to 'repair / service'... well, it's a bit tedious to put the o-rings back in, but it can be done w/o the expensive tools nor sending it back to Gar-Kenyon (who still offer repair services for a price...).

Once I figured out how to take it apart, as I expected there were only three o-rings, a couple teflon backup rings, and a 'circlip' that keeps the end 'gland' from popping out under pressure.

On the gland end of the device is a small screw and star washer... take this out, and with an angled pick, pop off the cover... behind this is the circlip (its a bent piece of square aluminum). Work the clip out with a pick, and now you can push the rod / piston assembly out the gland end. If there's any fluid left in it, be ready to keep the mess to a minimum... ask me how I know...

Pushing the rod / piston assembly out, you'll see:

The gland end pops out easily and has the large o-ring, this one is easy...
The rod end has two o-rings and teflon backup rings... this end... not so easy...

On the rod end there are two groves about 1/4" apart inside where the shaft rides... each groove contains a small teflon backup ring and a small 3/8" ID. o-ring underneath the teflon ring. You'll need to 'carefully' remove the teflon rings if you intend to reuse them. Do that first, then you can pick out the old o-rings. A set of dental picks from Harbor Freight worked really well here... but be careful not to scratch stuff or damage the teflon rings as you can reuse them if they are not damaged.

Clean everything and make sure there's no scratches / gouges in the shaft where it rides on the teflon rings, then you can put it back together.

Putting things back together is really trial and error but with patience you can do it w/o damaging the new o-rings / old teflon rings ...

I used the (cleaned) piston/shaft to help keep the o-ring from poping through from the inside, and I used a 1/4-28 AN bolt threaded into the end of the shaft and a small 1/4" drive extension to 'help' get the o-ring going into the groove. Do the outside most one first, then the second o-ring won't have anywhere to go except into the inner groove. Pushing the teflon rings back in, you have to push them into the grooves, using the piston/shaft to prevent them from popping thru to the inside. If they look a little 'ugly' you can smooth them out on the rod end / shaft and once they are installed use the drive extension to smooth them into the grooves before you attempt to push the shaft all the way through during final reassembly.

Once you've got the piston/shaft back in the body, pull the rod all the way out to the end and clamp the unit upright into a bench vise you so can fill it with hydraulic fluid. You'll need to 'bleed' the trapped air out to make things work correctly...

You do this by pressing the end gland and its new o-ring into the body, some fluid will escape when you do this, but there will still be air trapped behind the gland. Next hold the end gland in place with the palm of your hand (covered with a paper towel as hydraulic fluid will leak out while you do this) and simultaneously slowly push the rod 'up' towards the end gland... air and excess hydraulic fluid will be expelled during this process.

Once you've pressed it all the way to the end gland, you can put the circlip back in so the end gland can't pop out under pressure. At this point you should be able to pull the rod back to the other end (away from the end gland) and there should be resistance. Push it back towards the end gland, there should be full motion AND you should feel resistance. If it seems to get 'stuck' in either direction, you've still got air trapped inside. Repeat the bleeding process.

If you did everything correctly, you'll have good resistance in both fore/aft travel of the rod and you won't have any leaks at the rod end nor at the gland end.

Sorry,... I didn't get pics while I did this, I just started the process and had hydraulic fluid all over myself and didn't want to get it on my phone... LOL

Here's the O-rings you need:
qty 2 - MS28775-013
qty 1 - MS28775-118

I re-used the teflon backup rings and the circlip as they looked fine, so I don't have the p/n for those.

PM me if you need help or have any questions
sk
 

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