The Stovebolt Site Forums The Shop Area General Truck Talk Bump steer isues on 51 half ton.

After 30 years of ownership my truck was no longer fun to drive.My drag link was wore and i was unable to remove the ends or tighten them.Tryed penetrating oil,torch,and they wouldnt budge.I got out the sawzall and cut off the ends and replaced the draglink with a new one.WOW,WHAT A DIFFERENCE.I still have a small amount of bump steer.I adjusted the steering gear but havent tryed it yet.i was wondering what all will cause bump steer?

I have wondered for years, what exactly is "bump steer"?

Joe

Slow..Rider,

Using my definition of bump steer, you would have had to change some steering geometry to create this problem. Just changing the drag link without altering the linear (?) relationship of steering arm and pitman would not create it.

Are you sure something in your retrofit isn't loose or adjusted wrong and you are merely having a tracking problem.

Bump steer is just that, when you front wheels hit a bump, the upward or downward movement of the axle changes the distance from steering arm to pitman arm which either pulls the steering arm or pushes the steering arm which causes the truck to steer right or left...without you turning the wheel.

If the angular plane of the drag link to steering arm and pitman arm isn't flat, a bump will shorten the distance or increase the distance which will tend to drive the wheel one way or the other.

This is how I have always understood it.

Stuart

Bump steer is the truck going the way it wants when going over a bump,veering one way or the other,not the way its pointed.The problem existed before changeing the drag link.Changeing it improved but did not eliminate it.

hey slow
the cause is ''in theory''
http://www.naxja.org/html/techarticles/bumpsteertech.htm
http://www.bakerprecision.com/longacr17a.htm
see the tech tip
talk about a difference in steering
http://www.stovebolt.com/techtips/draglink_adjustable.html

If you read those two articles you will see that both of them apply to designs other then the original AD truck. It has to be something altered about the geometry of the front end components that is incorrect to cause real bumpsteer in these trucks.

Just my $.02 but I think folks have a tendency to catagorize many handling problems as "bumpster." As pointed out, a fairly tight stock front AD suspension on a decent road surface should track straight as an arrow. You don't have to accept less because you're driving an "old truck."

I contend that if your front suspension is in reasonably good condition, that a check of the toe-in and the addition of just a tad more will remedy the condition. It's the easiest thing to check of the 3 critical "adjustments" and I've found that in 90% of the cases it remedied the situation. You don't want to go overboard to a point where you're "plowing" and eating up your front tires, but an extra 1/8" might just improve the situation. It doesn't cost anything to try.....take your measurements, establish your baseline, and see if it doesn't remedy the situation.

In addition, I've found that adding a shimmy dampener/steering stabilizer helps to reduce the wear and tear on a straight axle front suspension. It won't cure your tracking problems but it will save you time and money in the long run once you get your truck to handle like it was designed.

I run a tank of gas through my 54 truck every week and travel on varied road surfaces and running at 70 mph shouldn't be a "white knuckle" experience. After all, what's the fun of owning and old truck if you can't enjoy the driving experience?

Dave

What exactly are we talking about here? Is this a stock-height, straight axle truck? What year?

The articles in the links above are referring to IFS problems. The stock suspension on an AD for instance has little to no bump-steer, but has a limited amount of something called "roll-steer" that can't be avoided. It all boils down to the same thing though, Stuart pretty well nailed the definition of it I think.

I had severe bump steer after modifying my straight-axle suspension. It was caused by the drag link no longer being parallel to the frame. I would assume that even a stock truck with 50 year old springs might set quite a bit lower than it did when new. Anyhow, the remedy is pretty simple, level out the drag link. I did this by a combination of: 1. raising the steering box, 2. shortening the pitman arm, 3. bending the steering arm on the driver's side down. I had to do all three to get the drag link level since the ol' girl sits about 6" lower in front that stock.

I'm happy to report - NO bump steer anymore.

Edit: The software gremlins took the word "link" and magically tied it to something irrelevant.

Thank you all for your input. For the record its a stock original 1951 1/2 ton stepside with the only mods being a 235 and 15 inch radial tires.The only front end parts ive replaced are the king pins and the drag link. Ron.

Take a look at your drag link. Is it sitting fairly level?

The drag link apears to be level.I took it out today after ajusting the sterring box and that seemed to improve things,still some minor bump steer.I do have abought 3 inches of play in the wheel and was wondering if that would have anything to do with it.

You should be able to get most or all of that play out of there and then you'll think you're driving a new truck.

Go to Wallyworld and get a cheap fish scale, then follow this procedure: http://chevy.tocmp.com/shop/1948_51truck/51ctsm0903.htm

Slowrider,
if the bushings are worn in your steering box, you will not be able to take all of the play out of the steering. It may feel like it on the sdjustment but when you move it from side to side, the pitman arm will jump making a clunk. That would allow the steering to drift without input. A box with this problem will not hold fluid even with a new seal.