Solving Nose Wheel Shimmy Once and for All: A Practical Guide for Cessna Owners

One of the most irritating and frustrating parts of flying a Cessna single is the notorious nose wheel shimmy. The nose wheel shimmy fix is a known problem that has affected scores of aircraft over the decades. Still, it can also be a serious issue for the plane and the pilot, as was witnessed in a 2013 incident in which the nose landing gear collapsed on a C-206 in Boise, Idaho.

This problem has been known for over 4 decades, with Cessna acknowledging it in the SE84-21 Service Information Letter. We tackled this topic over three decades ago, with our tech team writing our first tech note on it, which was appropriate, as it impacts so many Cessna singles.

Let’s take a look at this issue and the Cessna nose wheel shimmy fix.

Start With the Balance: Tire and Wheel Assembly

The first place to start is with the nose wheel/tire assembly. Aircraft tire and tube manufacturers paint a red dot on the tire for the “light” spot. A yellow stripe on the tube, or the valve stem, should be aligned with the red dot for coarse balance during tire buildup. Then the tire/wheel assembly is balanced with a static (bubble) balancer, which generally does an acceptable job.

Dynamic balancing is the single most crucial step in diagnosing and correcting shimmy. Static bubble balancing may work in some cases, but spin balancing ensures proper dynamic alignment. And sometimes there is no other way to get them balanced other than using a dynamic or spin balancer. However, most aircraft shops do not have a dynamic balancer.

One option is to find a motorcycle or powersports shop that has a balancer, as they usually have mandrels that work for the wheels. The tire will be balanced using lead weights just like a car or motorcycle tire.

There have been cases where an owner got a brand-new tire that would simply never balance correctly. If this happens to you, you need to send it back for a different tire or a refund. This is a bad tire, and you will only create more problems by trying to stick it out.

Tire Condition and Roundness

Tire condition is the next step in the process. After you have checked the tires for proper balance and balanced them, check their physical condition. If you have ever been driving down the interstate and noticed your car riding extremely rough, a broken belt in the tire is a common culprit. Well, the same thing happens in aircraft.

If the belt is broken, you will notice a wicked shimmy, although it will be fairly obvious if the shaking and shimmying occurs at a position other than the nose landing gear that it isn’t the problem.

Finally, tires can and do often get out of round. An easy way to spot if a tire is out of round is to spin the tire on an axle and look from both sides and from the end-on. You should have no problem noticing if a tire is out of round from these angles.

Inspect the Torque Links (Scissors)

The torque links connect the nose tire/wheel assembly to the fork, and the steering collar and shimmy dampener. Therefore, any wear, slop, or looseness in the torque link bolts, spacers, or bushings will allow the shimmy to continue, undamped by the shimmy dampener.

For testing, temporarily replace the torque link castle nuts with self-locking nuts and perform a controlled taxi. The self-locking nuts are tightened tightly than a castle nut (which should not be particularly tight; already read the torque specs for castle nuts to avoid overtightening). If oscillation continues during high-speed taxi, you need to re-bush and replace all spacers and bolts as a set.

Always use the correct high?strength NAS bolt marked with a triangle head or part numbers NAS?464?/?NAS?1103?/?NAS?6203. Pricing has increased substantially since this technical note was published in 1996, but you should be able to find the appropriate hardware with the listed specs.

Steering Collar and Shims

The steering collar and shims are a problem area that is routinely missed when a nose wheel shimmy is noticed. The upper end of the torque links attaches to the steering collar, so the shimmy is transmitted from the wheel to the torque links, then to the collar. The collar must rotate only around the strut; any vertical motion, up or down, will cause binding and ultimately a shimmy.

If cocking is detected or shimmying continues after all other solutions have been attempted, removal of the entire nose landing gear will be necessary to re-shim the collar. So, check for excessive play or “cocking” in the steering collar—a common hidden cause of persistent shimmy.

Watch for vertical movement while another person shifts the wheel with a towbar.
Re?shim the assembly using standard shim sizes (.006, .012, .020?in.) to remove play and restore alignment.

Shimmy Dampener Function

Finally, we have the shimmy dampener. This small unit is a closed chamber full of hydraulic fluid. When a shimmy occurs, the motion is damped by hydraulic fluid being forced through a small hole in a movable piston.

These units have failed due to fluid leakage past the shaft and end cap seals, which breaks down the seals. Also, the piston shafts have bent, rendering them useless.

These are functionally the same as a steering dampener commonly used on full-size pickups and SUVs. They are used on large vehicles that tend to “wander” on the road, and the same principle is used here.

Since you know that the dampener absorbs movement through hydraulic resistance, be sure to verify the following before service:

Fluid leakage or degraded seals and O?rings.
Bent piston shafts or elongated attachment bolt holes.

Remember that a faulty dampener will not cure shimmy unless wheel balance and mechanical joints are corrected first, so make sure to check all other items listed here first.

Key Takeaways and Prevention Tips

There is an order you need to follow to isolate the cause of the shimmy systematically. We all know that throwing parts at a problem is inefficient and ineffective; careful diagnosis saves time, money, and frustration.

Begin every shimmy diagnosis by dynamically balancing the wheel and tire.
Replace worn torque link hardware entirely rather than piecemeal.
Correct collar motion through proper shimming and inspection.
Only rebuild or replace the shimmy dampener after confirming all mechanical causes are resolved.

Parting Thoughts on Shimmies

There are only five primary sources of a shimmy on a Cessna single: nose wheel and tire imbalance, nose tire condition, torque links, steering arm collar shims, and the shimmy dampener.

By walking through each of these in order, you will find the Cessna nose wheel shimmy fix culprit and fix it without spending undue time or money on the project. Oh, and be aware that it could be more than one factor, so always test the results, and if you have rectified one problem, move on to the next.

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