604-530-9160 sales@dalesauto.ca

What is “Death Wobble”?

What is “Death Wobble”?

First of all you have to understand the dynamics involved before you can fix this issue.

“Death wobble”

Is a phrase used to describe a quick oscillation of primarily just the steerable wheel(s) of a vehicle. Initially, the rest of the vehicle remains mostly unaffected, until translated into a vehicle yaw oscillation of increasing amplitude producing loss of control. Vehicles that can experience this oscillation include motorcycles and bicycles, skateboards, and in theory any vehicle with a single steering pivot point and a sufficient amount of freedom of the steered wheel, including that which exists on some light aircraft with tricycle gear where instability can occur at speeds of less than 50 mph; this does not include most automobiles. However, coil-sprung vehicles with a track bar setup such as the Dodge Ram 25/3500 pick-ups, Jeep WJ, XJ, ZJ, TJ, and JK with both stock and after-market suspension lifts may also have this problem. The initial instability occurs mostly at high speed and is similar to that experienced by shopping cart wheels and aircraft landing gear.

 

 

“Caster Flutter”

One major disadvantage of casters is flutter. A common example of caster flutter is on a supermarket shopping cart, when one caster rapidly swings side-to-side. This oscillation, which is also known as shimmy, occurs naturally at certain speeds, and is similar to speed wobble that occurs in other wheeled vehicles. The speed at which caster flutter occurs is based on the weight borne by the caster and the distance between the wheel axle and steering axis. This distance is known as trailing distance, and increasing this distance can eliminate flutter at moderate speeds. Generally, flutter occurs at high speeds.

What makes flutter dangerous is that it can cause a vehicle to suddenly move in an unwanted direction. Flutter occurs when the caster is not in full contact with the ground and therefore its orientation is uncontrollable. As the caster regains full contact with the ground, it can be in any orientation. This can cause the vehicle to suddenly move in the direction that the caster is pointed. At slower speeds, the caster’s ability to swivel can correct the direction and can continue travel in the desired direction. But at high speeds this can be dangerous as the wheel may not be able to swivel quickly enough and the vehicle may lurch in any direction.

Electric and racing wheelchair designers are very concerned with flutter because the chair must be safe for riders. Increasing trailing distance can increase stability at higher speeds for wheelchair racing, but may create flutter at lower speeds for everyday use. Unfortunately, the more trail the caster has, the more space the caster requires to swivel. Therefore, in order to accommodate this extra swivel space, lengthening of frame or extending the footrests may be required. This tends to make the chair more cumbersome.

Caster flutter can be controlled by adding dampers or increasing the friction of the swivel joints.[2] This can be accomplished by adding washers to the swivel joint. The friction increases as the weight on the front of the chair increases. Anytime the caster begins to flutter, it slows the chair and shifts weight to the front wheels. There are several online anti-flutter kits for retrofitting wheelchair casters in this manner. Other methods of reducing caster flutter include increasing swivel lead, using heavier grease, reducing the mass of the wheel, or increasing friction with the ground by changing materials.

 

alignment01

 

This is a very common issues that are very common to a few automotive brands out there. The two most common are Dodge 2500/3500 trucks and Jeep Jeep WJ, XJ, ZJ, TJ, and JK. These vehicles have very similar suspension systems that tend to be more prone to this condition. Even in stock trim(tires, suspension) the “death wobble” symptoms can happen, now if you add larger tires and suspension modifications to the mix the chances of death wobble happening increases.

Dales Auto Service has seen many different scenarios that will cause this and it is not only one or two things that bring the symptoms to light. It can be something as simple as the front tires being out of balance or to high air pressure coupled to a worn steering damper. We have a process in place to diagnose the issues and to repair at a cost effective rate. We see many manufacturers offer their “fix” to the problem and many times their part will help but 9/10 it is a combination of parts, wheel alignment etc. that will correct the issue.

If you have had the dreaded “death wobble” experience and you do not feel confident driving your vehicle please call Dales Auto Service anytime, 7 days a week. We will fix the problem and bring your confidence back in driving your vehicle.

 

Share This