Cessna 205 Nose Strut, Steering and Shimmies
Last week after seeing my Nose Strut lower than it was supposed to be I checked my log books and the last time I completely serviced it was 5 years ago. I had put Nitrogen in the strut last year.
So, I decided to disassemble the strut and replace the “O” rings and other worn parts. Since I am OLD and no longer do aircraft maintenance work 7 days a week this is a big deal for me. But if I do it myself then I know it will be correct. Also, this is not considered allowed Preventive Maintenance.s
I thought I would explain the process and what to look out for because many A&Ps are not aware that the 205 Nose Strut is different. Many years ago I was in this same inexperienced position. Making simple mistakes in this process can get someone hurt. Remember telling you I was OLD, I stupidly didn’t take pictures, so I copied images out of the 200 Service Manual Section 5B and Figure 35 out of the Parts Manual to help explain what I am writing about. I will use part numbers when I can.
Safety first. Chock the aircraft on both mains and use what ever process you use to raise the nose wheel. Follow the process in the service manual to remove the Nose Tire and deflate the Nose Strut. Remove the lower bolt on the Torque Link.
If you go to illustration 5B-7, (enclosed), you can see that the C205 has a different style Torque Link without a flat centering device to center the nose gear when the strut is extended. Most other Cessna aircraft have the type of Link with the flat spot that when the nose gear strut is extended it locks the Nose Gear straight. Since the C-205 does not have this flat spot they need to have a different way to center the nose gear when the strut is extended, while allowing it to turn with the rudder pedals while it is on the ground.
Look at the illustration Figure 35 of the parts manual. You will notice # 38 and # 58 shown larger on the top right of the illustration. They are brass sleeves with one end of each cut on a 45 degree angle. Notice # 38 has a slot on the top inside and # 58 has a slot on the bottom outside. Then there is pin # 39, but there are 2 of them. # 38 is slid over the top of # 1, the lower strut, and # 39 is mounted in the middle and has a bunch of “O” rings and backups as shown in Illustration 5B-3, (enclosed, you can see it in the center of the page). The little pins discussed before slide into the slots on the strut # 1 and #38 and on the bottom outside between #59 and #17 the Trunnion. These pins lock their respective pieces together, so they cannot turn. This explains how the centering works when the strut is extended and locks in place.
All this being said, this is where the problem comes in. When the lower strut is pulled out of the Trunnion the one little pin #39 falls either on the floor or into the hydraulic fluid and is lost, out of the strut, when it is disassembled. Not knowing this pin # 39 is there and no specific mention in the re-assembly instructions it is left out, lost at least until this happens.
You take off and apply right rudder or left rudder sometime in your flight. If all pieces especially the pins are in place the rudder turns, but because the Nose Gear is locked, straight, the Nose Gear doesn’t turn, and the Nose tire hits the ground straight when you land. That is if you land straight.
But if a pin is missing when you apply rudder pressure in the air the nose gear will turn, because there is nothing to keep it centered. And you will not know it. Now when you land you will head for the side of the runway that the wheel is turned to.
Don’t ask me how I know how exciting this can be.
If someone works on your Nose Gear, lift the nose until the strut is locked and using a tow bar see if you can turn the Nose Gear. You should not be able to.
Hope this discussion about how the Nose Gear centering helps you 205 drivers become safer pilots.
The second part of this discussion is about some shims that are in the Nose Gear assembly and you should check them while the lower strut is out, because it is easy. Cessna never expected these aircraft to last as long as they have, so even though they had a way to set up the Nose Gear at the factory they never explained in the Service Manual how to set this up. I met an OLD Cessna assembly guy and he explained how to do this. I will pass it on. This works on all the other Cessna aircraft also. Anyone who has a problem with a Nose Gear shimmy, this is the cure most of the time. Of course, all the other parts need to be rigged also. After fixing this, please don’t put a shimmy scuffed up tire back on the airplane.
The shims are listed in Figure 35, #42. When you go to the parts list you will see Cessna has 3 different shims of different thickness. Also, # 40 is important. If you need to replace the shims replace these washers also. There is 1 above and 1 below the collar assembly, # 41. They all work together.
The trick here is to use a feeler gauge and see if you have more then .012 between the washers and the shims. Check 3 or 4 different places around the collar. If you do, anywhere, then you have a problem.
To fix this take the snap ring # 60 off, disassemble the collar assemble, clean everything very well. Clean it again. Then look at the collar which has a bearing inside. If that bearing looks damaged or rusty, replace the collar. The bearing can’t be replaced by itself. If it looks good and it is clean, because you cleaned it well, put it back together with new washers and measure the space with feeler gauges between the collar and the washer. THIS HAS TO BE DONE DRY, NO GREASE. What ever that amount is add shims so that you have less than .012 DRY. Then take it apart, grease pack the bearing, and re assemble with the shims. It will be hard to get it back together with the grease packed in it. This is how they were set up at the factory. DO NOT USE ANY OLD SHIMS. They might look good but trust me, they are worn somewhere if you had more than .012 to start with. This will fix 99% of Nose Gear Shimmy problems.