Ask Away! with Jeff Smith: Fixing a Dangerous Front-Wheel Shake in a Vintage Chevy II

I have a Chevy II with a 355 cubic inch small-block and a Muncie four-speed. Over the years, I’ve made some small suspension modifications with Global West De-A-Lum bushings. On the freeway, the car can get into a violent front-wheel shake where the steering wheel wobbles really badly in my hands. It gets so bad that I have to stop and then lightly get back up to speed. It seems to happen more often when I give it more gas. It’s so bad I don’t want to drive the car until I can get it fixed. What should I do?

C.T.

Jeff Smith: The Chevy II is a great little street car that is light and fun to drive. But while it’s small and nimble, the front suspension leaves much to be desired compared to its larger Chevrolet cousins.

The front suspension is different because the coil spring is located above the upper control arm rather than between the upper and lower control arms as it is on cars like the Camaro and Chevelle.

The steering linkage creates a serious bump steer issue when the suspension runs through its entire length of travel.

Bump steer is a term used to describe massive toe changes aggravated by big camber changes that occur as the front suspension moves through its entire length of travel.

Let’s start by looking at one side of the car. We’ll choose the passenger (right) side looking at the suspension from the front.

As the front wheel moves through its suspension travel, the spindle creates an arc as it moves up and down because it pivots from both the upper and lower control arm mounting points. The steering linkage is hooked to the spindle through the steering arm and if everything is right with the world, it would create the same arc as the spindle.

Unfortunately, the Chevy II doesn’t work that way and the arc of the steering arm is different than the arc for the spindle. These converging/diverging arcs move the steering arm to create either toe-in or toe-out depending upon the changes in the arcs. This toe change is called bump steer and the problem is often magnified by worn parts and/or poor alignment.

The most common cause for this kind of problem is usually a worn idler arm or drag link, or both.

The drag link is the long linkage rod that connects the steering box to both left and right tie rods. The idler arm is used to support the steering linkage on the right (passenger) side and to maintain the height of the steering linkage opposite the Pitman arm connected to the steering box.

Unfortunately, the Chevy II idler arm and the drag link are fitted with rubber bushings that wear quickly. When the idler arm and/or drag link become sloppy, this allows the steering linkage to move which will aggravate the front suspension’s already-precarious bump steer issues.

An easy way to test the idler arm is to jack up one front corner and support the car with a jack stand beneath the subframe.

With one corner of the front suspension off the ground, use both arms to move the front tire and see if things feel loose. Watch the idler arm and drag link carefully, followed by the tie rods. If there is movement in the steering linkage, you’ve found your problem.

Next, place the floor jack under one of the lower control arms to remove the spring load from the ball joints. Now place a long pry bar between the tire and floor and attempt to pull upward on the outer end of the pry bar. If the ball joints are in good condition, you should feel no looseness or movement. If you can feel movement or clearance, it could also not be ball joints but simply loose front wheel bearings.

Another possible wear point is either upper or lower control arm bushings but you say you have the Global West Del-A-Lum bushings which are excellent, so unless you’ve put 100,000 miles on them, they should be okay. Still, it would be worthwhile to check them for wear.

Another potential wear point is the strut rod bushings. These can be replaced with higher durometer bushings that will deflect less. If the strut rods are moving under load, that could also be causing the problem by allowing the lower control arm to move fore and aft—which it shouldn’t do.

Another issue is the car’s alignment. While technology has made alignment racks more accurate and sophisticated, this tends to work against owners of older vehicles.

Not long ago, you could take your car to an alignment shop and tell the technician the alignment specs you wanted. Today, only specialized shops can perform a custom alignment. This is because many “big box” shops use computerized machines that only allow the stock specs listed in their software. I’ve been told more than once that shops will inform an enthusiast that they can only set the alignment to the stock specs and that custom alignments aren’t possible.

We recommend calling the shop beforehand to determine whether they will help with performance settings. It’s also possible that a non-stock alignment request can be used as an excuse to not mess with the car.

What’s disconcerting is that the stock specs for most ‘60s cars are a long way from what most would consider a proper alignment.

Here’s why this is important:

The factory specs for a ’66 Chevy II is to set the caster at +1 degree, the camber at +½ degree and the toe-in at ¼- to 3/8-inch! For those of you who know what these specs mean, these are a far cry from acceptable.

A better generic spec would be 3-4 degrees of positive (+) caster, ½- to ¾-degree of negative (-) camber, and a total of 1/16-inch of toe-in, or 1/32-inch of toe-in per side.

Those 1966 factory specs were designed for bias-ply tires and according to our friend David Pozzi—who knows much more about suspension dynamics than we do—when the industry went to radial tires, it became common practice to reduce the toe-in by about half.

The “generic” specs we listed are aimed at improving handling. We won’t get into the details on alignment since that could demand a lengthy discussion. If you want to know more—ask a specific question and we’ll try to answer it.

Back to the Chevy II.

It’s possible that it would only take a combination of perhaps a worn drag link, idler arm, and perhaps a less-than-ideal alignment to create the situation you describe. Global West will rebuild your existing drag link and idler arm with Del-A-Lum bushings if you send them the pieces. If there’s any question whether your parts are worn, we suggest improving the drag link and idler arm, along with adding Global’s lock-out plates that eliminate the eccentrics that set the camber.

Those original eccentrics had a bad habit of moving, which immediately alters all the other specs. So the lock-out plates are an ideal addition. But pay attention to the idler arm and drag link first.

In our research we also uncovered a company called Open Tracker Racing that mostly specializes in early Mustangs, but because the Chevy II front suspension is similar, they make a neat rollerized lower spring perch mount to replace the stock rubber mount that, even when new, tends to bind and reduce freedom in suspension movement. You might want to check them out as well.