Tail Wagging the Dog

February 2, 2009

477

February 2, 2009

Steering problems can manifest themselves in many different ways-and in some instances, it isn’t the steering system that’s to blame. One of the most common problems we address at Henderson’s Line-Up is an issue we call “Tail Wagging the Dog”. It’s the sensation you get when the coach seems to have a mind of its own; you steer the wheel back and forth, and the rear half steers the coach.

The first coach we really experienced this on was a P32 chassis; we checked the steering gear, we tried adding stiffer springs, added a leaf on each side. It wasn’t until my brother, John, discovered that the bolts on the rear leaf spring pack had moved far enough in either direction to make contact with the adjacent spring hanger bracket. That could only mean that the axle was moving from side to side-and that was causing the loose sensation in the steering. Those early coaches only had 2-inch wide leaf springs, and they would flex. Plus, they had rubber bushings that would deflect, adding to the problem.

The newer Workhorse chassis have much wider, tapered springs, but the coaches are also bigger and heavier than they used to be, so the problem can still persist. Even the smallest amount of axle side-to-side movement can contribute to a “loose” steering feel, where the rear of the coach continues to move after steering input. The long wheelbase coaches, especially those with a long rear overhang are particularly susceptible; the overhang creates more leverage on the rear of the coach especially in high winds, etc. That leverage exerts its force on the leaf springs and bushings, causing them to flex.

So what we did to solve the problem was create our Trac Bar, which is essentially a large Panhard bar. It is mounted horizontally at one end to the frame of the coach, and the other to the axle, creating a rigid connection that stops axle side-to-side movement. The first time we installed our Trac Bar was on a Safari Trek motorhome; when the owner got finished with his test drive, the first thing he said was that the steering felt better.

It should be noted that coaches with air suspension should already be equipped with a trac bar of some kind from the factory, as air springs won’t do anything to control side-to-side movement. If your coach still suffers from Tail Wagging the Dog, you could have fastener(s) that have worked themselves loose and/or bushings that are getting worn out.

The lack of a Trac Bar, or a worn out/loose factory bar are not the only causes of Tail Wagging the Dog, but they are the most common. Other causes excessive rear overhang that creates weight distribution problems, which contributes to “light” steering feel. In these instances, we analyze the weight distribution of the coach and see if the ratios are where they’re supposed to be. If not, we may take measures to re-distribute some of the weight in the coach, even add some weight to the front (providing there is adequate capacity remaining) to correct the problem.

Tail Wagging the Dog is an issue that can affect both Class A and Class C motorhomes. Our manufacturing division, SuperSteer, offers Trac Bars for all popular coach chassis, and is developing new bars for other applications such as pick-ups and SUV’s. Once a Trac Bar is installed, you’ll find that the coach requires less course correction and reduced steering input. At left is a picture of our newest Trac Bar kit for the new Kodiak chassis.