April 24, 2017

The Danger of ‘Wheel-wobble’

• By John F. Chisholm •

The ‘Steering’ section of the service manual for my antique Land Rover refers euphemistically to a phenomenon it calls, “Wheel-wobble.” Really. Until recently, I read that perplexed. To exact what were they referring? How serious could it be? It certainly sounded benign.

Trust me. I am now experienced. ‘Wheel-wobble isn’t benign. Far from it.

Have you ever held a bicycle wheel by the axle and given it a spin? If you subsequently attempt changing the orientation of the wheel, the physics of the situation fights you. Hard. Essentially, the wheel has become a gyroscope. It takes surprising force to move it. It takes even more to calm it down afterwards. In fact, depending on the speed, weight and size of the wheel, even attempting it can be a major workout.

As it turns out, that’s exactly the issue the service manual refers to as ‘wheel-wobble.’

Now consider that the Land Rover wheels are much heavier than a bicycle’s. Plus, of course, we’re dealing with the steering, so there are two of them involved.

Remember as well that the Land Rover has four-wheel drive. The front axle pivots are intended to allow both power transmission and steering. (Please bear with me. There’s an important point to all this.) As a result, the upper pivots are spring-loaded to keep them in place. They’re nasty springs, big and stiff, held into place by four bolts. The service manual gives figures for the exact amount of compression. Shims are provided to achieve that tension precisely.

I did all that when I rebuilt the truck. I did it according to the specifications, too. In fact, I did it precisely according to the manual. I even rechecked my work, just to be certain.

None of that matters. Under certain circumstances, those springs simply don’t work.

That’s because any really serious bump further compresses them as the wheels are jolted upward on their pivots. It doesn’t have to be by much. No. That, in turn, has serious ramifications. Without those seats in place, the front wheels aren’t held tightly in their orbits.

The result?

‘Wheel-wobble’ wrests control over the steering from the operator. The front tires, rims and brake drums become out-of-true gyroscopes. The steering wheel jerks violently back and forth in your hands. Control is impossible. Certainly I couldn’t wrestle the truck back under my direction. I tried. Your only option is coming to a complete stop. NOW. Pray that you have enough room to do so harmlessly.

Curiously, once stopped, everything returns to normal. It fact, it’s difficult believing anything actually occurred, so benign has the handling become once again.

Whatever else that can be said about it, it was certainly terrifying. I was on a short jaunt around the farm, warming the motor oil prior to changing it. Call it driver inattention. I struck a frost-raised crosspipe with more violence than I would have normally. The steering wheel was literally jerked from my hands in the resulting reaction. In fact, a wheel spoke struck my left thumb with such violence that I’m losing the thumbnail. Fortunately I had the space to stop the vehicle safely.

What I experienced was a design flaw. A serious one. I’m guessing that this issue caused the early demise of the Series II Land Rovers. They lasted only two years before the Series IIA came out with a vastly improved steering apparatus (among other improvements).

Today, my Land Rover is no longer completely original. I admit it. Like most Series II owners, I’ve changed my steering over to the newer arrangement. I did the job last Monday. It took all day. (Remember, I had to convert both sides.) Nevertheless, I did what I had to do. I consider it time and effort well spent.

It’s worth learning from the experience that however benign a euphemism such as ‘Wheel-wobble’ may sound, untreated, it can still kill you.