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I am well into my second thousand of miles since putting my truck on the road (57 3100), and it is a challenge to drive. I have the original straight axle with new kingpins and new tie rod ends, and 76 Chevy pickup power steering. Wheels are 15 X 8" rally with 235/70 Goodyear Eagle rubber, and the Goodyear dealer aligned it. If you read the anecdote at the bottom of page 15 in the June issue of Vintage Truck, it describes my experience perfectly. There is nothing loose, but the truck is all over the road, especially when it hits a bump, goes over RR tracks, or is subject to a quick flick of the steering wheel.

The Vintage Truck article suggests that returning to a narrow wheel will correct the problem. I sure like the looks of those 8" rallys, but I would rather enjoy the drive. The Goodyear techs said there is no adjustment to those old straight axles except the toe-in. My mechanic says the steering feels like a caster or camber out of whack, and that there are shims which can be inserted or removed for adjustment. The only place I can imagine inserting shims is between the axle and the leaf spring, and,since I put the truck together,I know there are no shims in it now. Help me out guys ??!!! Thanks in advance.

Russell;
There should be shims between the axle and the leaf spring. Any spring shop and most FLAPS should have them. I believe the factory put in about 3 degrees of caster so ask for 3 degree shims (one for each side). Install the shims with the wide end at the rear side of the axle, the narrow end towards the front.

This should help your problem.

The shim suggestion is right on for a caster adjustment, but there is no camber adjustment for the I beam axle on the GM trucks. If camber is out, that means the axle is bent (unlikely), and GM does not suggest bending to fix ( Ibeleive it can be done, with proper equipment and a knowlegable mechanic working on it). One problem with using the shims is that thay no longer produce the 2" shim that fits the light truck (no demand), but the wider 3' ones could be cut down to fit.
BTW, I have read that article, and agree with most of it. However, on the 8" rim part, there is a failure to suggest the other cure for the problem. The tire mentioned in the article (as well as what you have on your truck) are actually too narrow for the rim. That size tire is better suited for a 7" rim, not an 8". So the other option would be a wider tire, perhaps a 255/70/15, or like what I have on mine, a 30x9.50x15 C. That will correct a wander. due to a rim/tire mismatch. Same applies using a wide tire on too narrow of a rim. The rim must support the sidewall correctly for proper handling.

If the caster shims do not fix your problem, I would find an alignment shop that does large trucks with straight axles. These axles can be cambered and are able to provide you with a safe driving experience. There is no reason why a "tight" front straight axle suspension should not perform as well as any modern "tight" suspension. The only difference my be ride quality, but remember, it is a truck.

Have you considered a steering stabilizer? I believe they are available but not sure. I'm not a mechanic but my Jeep had exactly those symptoms and a new steering stabilizer corrected the problem.

Here is what you need, you can get them at NAPA as well as the supplier in the link.
http://www.chevsofthe40s.com/browse.lasso?&dept=Truck&cat=190T&skip=18

(next part up and down are more wedges)

My truck drives 100% better since adding a 2 degree. The factory setting may not be right any more if you changed the ride hight or front to rear angle. Start with 3 and reduce down if it to hard to steer when setting still. It will try to lift the truck when setting still if you have to much caster. Another way to tell if you need more is if the steering wheel doesn't return to center after making a turn.

To install them just loosen the front u-bolt with axle hanging, and slip them in. You should notice a change right off.

Joe

I grew up around a shop where we bent straight axles as a matter of every day alignment practice, so the idea that a camber problem can't be corrected is a bunch of hogwash. Camber problems cause sidways pull problems and inside/outside tread wear, however, not wandering troubles. If both wheels are approximately the same on the caster measurement, shimming the axle will help. If only one wheel is out, the axle will have to be twisted on one side to bring the caster into specification, not an easy task, but doable with the proper equipment.

One problem most people totally forget, or wish they could, at least, is wheel offset. When a noticeably wider wheel than original is installed, there's only one place for the extra width to go, toward the outside. This moves the tread centerline out, which changes the "scrub radius", the intersection of an imaginary line drawn through the kingpin, and one through the tread centerline. Ideally, these lines should intersect at the road surface to create a good pivot point for steering the wheel. In practice, the lines only do this on a very tall tire/wheel assembly (like the engineers put on the truck when it was new!) Shortening the spindle-to-ground distance with a low-profile tire, and/or a smaller-diameter wheel, plus moving the centerline out creates a great deal of leverage on the spindle, creating- - -you guessed it- - - -steering wander! Increasing the caster will reduce, but not eliminate the problems created by installing those cool-looking, but totally incorrect tires and wheels. The only proper fix would be to re-engineer the axle dimensions to accomodate the shorter, wider wheels by changing the kingpin angle and scrub radius.

Also, be sure the steering gear is exactly on center, and the sector preload is adjusted correctly. There should be absolutely no free play at the center of the steering travel, and the wheels should point straight ahead at that zero-clearance point. Sector gear preload is adjusted with the Pitman arm disconnected, and the turning torque at the steering wheel center nut should increase approximately 10 inch-pounds as the wheel rolls over center. Adjust the sector preload nut on the side of the steering gear opposite the Pitman arm to adjust the preload. Once that adjustment is made, be sure the wheels point straight ahead with the steering gear centered by adjusting tie rod ends.
Jerry

Excellent post Hot Rod except you can't center the steering gear on a sraight axle truck useing the tie rod ends. You can on IFS. About the only way is to build an adjustable drag link. That gets into a whole other discussion.

Good catch! Of course, if you read the original post, he's already modified the steering somewhat, with some sort of power-assisted steering gear, so there's no telling how much inaccurate steering geometry he's dealing with. I seriously doubt if any 3-axis trigonometry got involved in swapping that gearbox. It's possible he's dealing with massive bump steer in addition to the caster, scrub radius, and other troubles. Some hotrodded steering systems are downright deadly in anything but a slow-speed straight line.
Jerry

Great suggestions, and thanks to one and all. For Hotrod, I can confirm that there was no 3-axis geometry applied to the power steering swap. I bought a kit from Chevy Duty and a PS pump and box from a junk yard, and followed the instructions.

I appreciate the description of the intersection of imaginary lines, and why wider tires lead to problems. I certainly don't want wider tires on the truck, because the ones I have already scrape the inside of the rear fender with any kind of load.

Please explain 'bump steer'.

I didn't think a beam axle vehicle would have problems with bump steer. As I understand it, with IFS, if you hit a bump at speed the suspension would 'collapse' then rebound, changing the camber and possibly the caster temporarily.

The fix involved removing the front springs and jacking the front end of the vehicle through it's full travel, measuring caster and camber at various heights. Then add/remove shims until the caster and camber changes are minimized. For F1 cars the suspension mounting points are adjustable to get bump steer to 0.

Brake squat can also be minimized the same way. You don't really want to go nose down when you hit the brakes because it unloads the rear wheels.

Unfortunately, I don't think that there is enough adjustment built into modern IFS systems to get true 'neutral' steering.

Sorry. That should say anti-dive instead of brake squat. Anti-squat is a slightly different thing.