This is the third, and last post in the series about rebuilding the Globe Swift landing gear. In the first post I covered the rebuild of the Swift landing gear downlock and in the second I described the rebuild of the Swift landing gear actuator. In this post I will cover the removal, disassembly, installation of seals, reassembly and reinstallation of the Adel landing gear strut. I used Swift Parts Store rebuild kits S-145 (Adel strut seals) and S-144 (landing gear bolt and bushing kit) in this project.
I am writing these maintenance articles to make it a little easier for individuals to rebuild the Swift hydraulic components. This is NOT intended to be comprehensive or step-by-step advice about how the rebuild of these components should be completed. In order to accomplish this work you must hold either an A&P or AI certificate or you must be supervised by an individual who does and you must have in your possession the manuals and tools necessary to accomplish the task. I do not discuss all of the steps shown in the hydraulic manual. This is not considered to be preventative maintenance.
The Parts Book
The Swift Parts Manual and the Swift Hydraulic Manual both show this page when referencing the Adel landing gear strut.The Swift was built with two types of landing gear struts. The Adel strut is an oil-spring strut while the ELI strut is an air-oil strut. Both of the Swifts that I have owned have had the Adel strut, so I will only talk about that type of rebuild. I’ll leave the ELI strut to be discussed by someone more qualified.
As you can see from the diagram, in order to pick out the details of the strut assembly you will need a magnifying glass and some experience with cut-away drawings. The parts breakouts are described on an adjacent page. Some parts are described by their AN hardware designation and some are listed with a Globe part number. Often these Globe part numbers are also available with AN designations. As an example, breakout number 15 on this diagram is described as Globe part number 17284, but it may be purchased as an AN26-64 Clevis Bolt.
The simple explanation is to remove the four hanger bolts on each side of the upper strut and remove the strut from the wheelwell, however, several additional steps are necessary before you can do this. Since the intent is to replace the seals inside the strut, the strut will have to be taken apart and to do that the lower portion of the strut will need to be removed. That is the part that includes the wheel axle and brake assembly.
Since we have already removed the actuator and downlock, the actuator arm bolt has been removed and the upper actuator arms have been removed. There are two castle nuts with cotter pins on the front and rear of the upper part of the strut. Removing these will free the lower actuator arms.
Now might be a good time to remove the wheel and brake assembly from the lower strut and to remove the landing gear door. The doors on this airplane are the original Swift gear doors, held to the strut with two stainless clamps. You may be able to see in the right picture that this plane also has the braided brake lines running behind the landing gear door supports. That required dismantling the doors a little more than if the lines had been secured with cushioned clamps held by the door hardware. Lastly, the lower scissors arms will need to be taken off by removing the bolts on the upper and lower attach points.
The lower portion of the strut is held in place by a single bolt running front to rear at the bottom of the polished inner strut. This is actually a clevis bolt with a low-profile nylon lock nut on the rear side. When this bolt is removed, the lower strut may or may not slide down off the chrome strut. On this plane the left gear lower strut came off fairly easily while the right strut required ‘help’ in the form of dry ice, a propane torch and a rubber mallet. The Swift Hydraulic Manual describes the correct procedure to use.
Once the wheel, brake, lower strut and upper and lower retraction arms are removed, the four bolts on each end of the strut hanger can be removed and the remainder of the strut assembly can be removed from the wheelwell. With an empty wheelwell, you are now free to clean all that accumulated dirt, oil and grunge from the wheelwell walls and get it ready for your newly overhauled assemblies.
It is possible to dismantle the strut and replace the seals while the strut is still attached to the aircraft, removing only the lower portion of the strut and leaving the remainder attached to the aircraft. The process is described in the Swift Operating and Maintenance Manual (blue book). You might want to do this if only the strut was leaking and you didn’t plan on rebuilding the downlock or actuator. I wanted to do a more in-depth rebuild of the landing gear hydraulics, so I chose to remove the strut from the plane.
Dismantling the Upper Strut
The upper strut assembly will now have the hanger fittings/bushings and hanger tube attached to the upper ‘T’ portion. The hanger fittings/bushings are pressed onto the end of the hanger tube and attached with two clevis bolts, castle nuts and cotter pins. Remove at least one of the clevis bolts and you can remove the hanger tube from the strut housing. You will find the upper cavity full of grease, giving you an excellent chance to make a huge mess cleaning it out. (Remember: You’re not making progress if you aren’t bleeding, you don’t have chapped lips or you haven’t ruined at least one t-shirt.)
In the first photo you can see the top portion of the strut, the hanger tube and support brackets. The strut spring and metering tube are also visible the the right side of the photo. You can also see the threaded plug removed from the upper strut housing. The Hydraulic Manual tells you to be sure and remove this before dismantling the strut so that you don’t damage the bronze bushing when you remove it. The second photo shows the polished portion of the inner strut and the bronze bushing that is the home for the seals we are going to replace. The polished portion of the strut is held in the upper strut by a steel clip or ring that fits into a groove on the inside of the end of the upper strut. You can see a pin hole at the right end of the upper strut in the photo that can be used to work the clip out of the groove. I used a hydraulic press and a machined cylinder that fit over the polished strut and fit inside the upper strut, allowing me to compress the inner spring enough to access the retaining clip and remove it, then slowly relieve the compressing pressure to allow the spring to extend. I was actually pressing down on the end of the bronze bushing which was, in turn, resting on the flange at the top (left) end of the polished inner strut, pushing the whole thing down into the upper strut housing and compressing the spring. The flange on the upper end of the polished strut is referred to in one of the Swift recurring ADs.
Now the strut is dismantled and can be cleaned and new seals installed in the bronze bushing. Once that is completed and you have cleaned up the strut and wheelwell to your satisfaction, you can start the reassembly process, which is just the reverse of what we have just completed.
This last photo shows all of the strut parts in their relative positions and, I hope, gives you a better idea of the inner workings of the Adel strut.
Although this is an Adel strut, you may have noticed in some of the photos that there is an air fitting on the strut. Some Swift owners have removed the strut fluid filler plug and installed an air valve in its place. They have found that pressurizing the strut with 15-40 psi (opinions vary) of air pressure tends to keep fluid pressure on the seals and helps to keep them from drying out and leaking.
When you replace the bushings and bolts during the rebuild, make sure that the bushings allow unrestricted movement of the rotating parts. You want a snug fit, but not a clamping action as friction from the parts will add together to make the actuator work that much harder to retract and extend the gear.
Make sure that the retract arm bolt is installed with the head of the bolt to the rear and the threaded portion forward. This is contrary to normal aircraft hardware installation, but necessary due to the close clearances of the various parts when the gear retracts into the wheelwell.
When the reinstallation is complete, be sure to accomplish the Swift Landing Gear recurring ADs (47-06-01, 51-11-04 and 58-10-03), check the emergency extension cable routing and tension and accomplish normal retraction and extension operation and emergency extension.
I hope this has given you a better look at the inner workings of the Swift Landing gear parts and operation. If you have any questions about the process or the parts, please do not hesitate to send me and email or leave a comment.
One response to “Globe Swift Landing Gear Rebuild – Landing Gear Strut”
excellent information. well done