Possible cause for Cherokee nose wheel shimmy?

Timbeck2

Final Approach
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Timbeck2
Yeah, I've got it and it is somewhat controllable but my annual is due and I want it fixed. So far I've: serviced the shimmy damper, replaced the torque link bushings and bolts and replaced the wheel bearings. I'm going to remove the nose wheel and take it to Discount Tire to have the wheel dynamically balanced today. The only other option I know of is to adjust the rudder rods to the steering yoke to remove any play which my A&P will do. Am I missing anything? Anyone else have a shimmy story with a fix action?
 
I've got a 177B where it shimmys bad without tighting the axle through bolt more than I normally would. Nothing is obviously wrong with the axle or wheel parts.

Also, the holes in the nose wheel fairing were shot. The old nose wheel fairing is pretty heavy from being repaired mutiple times.

I've got a brand new fairing to go on which is much lighter. Hopefully it increases resistance to shimmy.
 
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Follow up questions: The red dot on a tire is supposedly the heaviest part of the tire, correct? If so, the red dot is supposed to go 180 degrees away from the valve stem correct?

Edit: disregard, the red dot is the light part of the tire.
 
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Check the part that connects the linkage to the nose gear. It being loose, will cause a shimmy.
 
If you do a search on this forum for "nosewheel shimmy" you will get an awful lot of results. I have posted numerous times that dynamic balance is the only way to address the root cause; everything else is either dealing with static balance or is aimed at suppressing symptoms.
 
The control horn on top of the strut has 2 bolts in it that can wear and cause shimmy. One goes through side to side and commonly wears the holes in the horn to an egg shape causing slop. The other bolt goes down through the top of the horn into the strut and wears as well causing slop. With the steering rod ends disconnected from the horn the should be NO play between the horn and the strut. If there is remove the horn and inspect the holes for elongation. If not worn replace the bolts with new and be aware they are not just bolts but are specific to the horn, as in not just any old AN bolt will do even if it apears correct. Order them by the proper part number. Next inspect the steering rod ends for play both at the rudder pedals and the horn. Repair as needed. Next jack the nose off the ground and grab the strut and try to lift it straight up. This is where I found my problem as the bearing adjustment lock ring on top of the strut was not safety wired and had loosened allowing the strut to move up and down about 1/2 inch. There was no preload on the strut bearings at all. Adjust the nose wheel bearing preload after checking the bearings. Balance the tire. Recheck the scissors to ensure there is no side to side play in them even though you installed new bolts and bushings. One or all of these things together should cure your problem.
 
Vaflier, thanks for taking the time for that excellent answer. Blue Rooster had the same comment. Dan, I did indeed dynamically balance the wheel yesterday (thanks to Adrian at the second Discount Tire I went to) and it required 1 3/4 oz of weight to balance the wheel which seems like a lot on a 6" wheel. The stick-on weights were placed near the valve stem and the red dot ironically. Today, the horn bolts and the bearing adjustment lock ring will be removed and/or inspected as my annual starts this morning.

Walt - thanks as well but grinding off good rubber seems to be more labor intensive in 112 degree heat and counter-intuitive to my issue. ;)
 
Slowing down and pulling back on the yoke always helped.

But now that it's solved:
 
Vaflier, thanks for taking the time for that excellent answer. Blue Rooster had the same comment. Dan, I did indeed dynamically balance the wheel yesterday (thanks to Adrian at the second Discount Tire I went to) and it required 1 3/4 oz of weight to balance the wheel which seems like a lot on a 6" wheel. The stick-on weights were placed near the valve stem and the red dot ironically. Today, the horn bolts and the bearing adjustment lock ring will be removed and/or inspected as my annual starts this morning.

Walt - thanks as well but grinding off good rubber seems to be more labor intensive in 112 degree heat and counter-intuitive to my issue. ;)

It's not uncommon to require that amount of weight. Aircraft tires are notoriously poorly made, often being way off balance both dynamically and statically, as well as out-or-round. The weights are stuck to the inside of the wheel at a very small radius and closer to the plane of rotation relative to a car's wheel, so it takes more weight to correct things.


McFarlane's balancer and the grinding off of rubber will only correct a static imbalance. Many of us here are old enough to remember when our cars only got a static balance job, and we put up with the steering wheel shaking constantly on the highway, with some particular speed being especially bad. The tires and steering parts suffered badly. In the '70s tire shops finally got electronic dynamic balancers and fixed all that, though primitive mechanical dynamic balancers had been available for ten years or more but were a pain to use. Most airplanes get, at most, a static balance, which is why nosewheel shimmy is such a frequent topic here. And most owners spend obscene amounts of money replacing torque links and bolts and shimmy dampers, all of which reduces the shimmy until those expensive parts get beat up again by the dynamically imbalanced wheel.

I built a mechanical dynamic balancer that I use on nosewheels. Stops shimmy dead. You can buy electronic balancers for smaller wheels such as motorcycle wheels but they cost $4K and more.

Aircraft main wheels can't be dynamically balanced. The brake disc is on the inside, and attaching the stick-on weights there won't work. The heat of braking will debond them. Dynamic imbalance on mains isn't much issue anyway; the gear's rigidity prevents noticeable shimmy and a static balance there makes things acceptably smooth.
 
I had a nose whee shimmy on the Bo that was cured by adding air to the nose wheel.
 
I've seen a Cherokee shimmy. At least I think she was a Cherokee. She was certainly Native American. Anyway, not sure I'd have tried to put a damper on that shimmy.
 
I've found that rotating the tire on the wheel can correct an imbalance problem with zero added weights.
But you'll have to add your own dot to locate the valve stem. :D
 
Yeah, I've got it and it is somewhat controllable but my annual is due and I want it fixed. So far I've: serviced the shimmy damper, replaced the torque link bushings and bolts and replaced the wheel bearings. I'm going to remove the nose wheel and take it to Discount Tire to have the wheel dynamically balanced today. The only other option I know of is to adjust the rudder rods to the steering yoke to remove any play which my A&P will do. Am I missing anything? Anyone else have a shimmy story with a fix action?

You state you serviced the shimmy dampener, did replace seals or just add fluid?
 
Both. But I've got a bigger problem. There is a pin and two stepped bushings that connect the steering horn to the strut. The problem is that the bushings aren't listed in the parts manual and the pin is different.
 
Both. But I've got a bigger problem. There is a pin and two stepped bushings that connect the steering horn to the strut. The problem is that the bushings aren't listed in the parts manual and the pin is different.
Sounds like your steering horn has been REPAIRED . Replace the horn with a good used or new one and new bolts or pins. Some of the Cherokees did use a pin instead of a bolt for the cross bolt in the horn. My 69 140 has no bushings in the horn just a bolt. All of them I have seen did not have bushings. You could have new bushings turned by a machine shop if you mechanic is willing to aprove it. What year and model is your aircraft.
 
Same as yours, my serial number is 28-26457. It is registered as a '69 but the finance company says it is a '70. My mechanic won't sign off on that and I don't blame him, I wouldn't either.
 
After finding two used steering horns and inquiring about the hole condition with no answers, I decided to bite the bullet and order a new steering horn and clevis pin. You never know what you're going to get with used. That together with the wheel balance should clear up the issue.

My "good" annual isn't good anymore. :(
 
I had a slight shimmy on my 66 180C. I replaced all parts that you have and it persisted.. I found that the bolt that runs through the middle of the bottom of the nose strut and through the square block. It was bent and wore out the lock.. I developed a "creak sound" replaced the bolt and the shimmy was gone.
 
That bolt, the bushings in the block and the other bolts and bushings in the scissor link have already been replaced.
 
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If you have not ordered the new one I would call Joe Jenkins in Delaware at 1-302-697-7743 and see if he has a good used one. If he sends you one it will be a good one. Great to deal with. Will not send you junk. Quite often will send it and a bill with it and you send him a check.
 
Dang it! Ordered the new one 2 hours ago from Chapparral. And one hour ago Texas Air Salvage listed one that I couldn't tell in the pictures the condition of the holes for the clevis pin for half the price of a new one, so it was "iffy" at best.
 
I feel your pain. These things are frustrating because it difficult to see or find a smoking gun. Everything that moves wears, all those flying cycles wears everything before it finally develops noticeable symptomatic problems. The cheap things are replaced first hopefully solving the problem but the other more expensive things get ignored till they can't be.
 
Dang it! Ordered the new one 2 hours ago from Chapparral. And one hour ago Texas Air Salvage listed one that I couldn't tell in the pictures the condition of the holes for the clevis pin for half the price of a new one, so it was "iffy" at best.

I tried . Sorry
 
Well, Chaparral hasn't shipped yet even though they have until the end of today to keep their "shipped next business day" claim. It wouldn't be the first time that I've ordered something and get an email back later informing me that they're "out of stock on that item." So, I'll keep that phone number handy in case the order falls through. It's all good.
 
Tubes may have a heavy spot mark, that should be taken into consideration when mounting a tire.

It's a yellow dot that identifies the heavy spot and should line up with the tire's red dot.

Even then, it's still a static balance and does nothing for shimmy, which is a dynamic balance problem.
 
Well the poo just gets darker the more we dig. Upon removal of the old steering horn, we discovered the bolt on top next to the strut fill schraeder valve (that gets saftied) was finger tight and the strut retainer ring was movable by hand. These things can't be found easily on a pre-flight. Looks like it was several issues all at once. Annual isn't over yet but I'm pretty confident my shimmy issue is resolved.
 
It's a yellow dot that identifies the heavy spot and should line up with the tire's red dot.

Even then, it's still a static balance and does nothing for shimmy, which is a dynamic balance problem.
Yes, so in cases like that, the tire red dot may not be oriented with valve stem, as expected. And if the tube and tire were oriented incorrectly, you wouldnt know without disassembly, and if incorrect, could require more weight to balance, statically or dynamically. I've seen wheels that have balance weight limitations noted in their overhaul manual. That is all. Hope OP has it fixed.
 
Well the poo just gets darker the more we dig. Upon removal of the old steering horn, we discovered the bolt on top next to the strut fill schraeder valve (that gets saftied) was finger tight and the strut retainer ring was movable by hand. These things can't be found easily on a pre-flight. Looks like it was several issues all at once. Annual isn't over yet but I'm pretty confident my shimmy issue is resolved.
Just what I had with mine. The bolt on top is a special bolt which can be had from spruce. I do not remember what is different about it but there was something.
 
It isn't anything special, just a close tolerance AN bolt with a specific torque. The manual states it needs to be saftied with .40 wire. Common is .20, .32, and .41. So I used .41. Hope the sky police don't show up.
 
It isn't anything special, just a close tolerance AN bolt with a specific torque. The manual states it needs to be saftied with .40 wire. Common is .20, .32, and .41. So I used .41. Hope the sky police don't show up.

Forgot to mention.. my bolt on top of the horn actually sheared one time.. didn't notice it until inspection but did find that the steering was much tighter feeling after that was replaced.


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