The Stovebolt Site Forums The Shop Area The HiPo Shop Bump steer questions and solutions

With my ifs conversion to my 49 6400 I'm concerned about bump steer with the narrowing of crossmember and drag link. Just a slight difference in drag length width to original placement will throw off the geometry of the steering system. If I have made a mistake in the measurement I will suffer additional bump steer than normal. My theory is to recut drag link bore the ends and thread them one right and one left then use a chtome Molly dual threaded shaft with jam nuts to be able to adjust length of drag link to correct bump steer. This would enable me to adjust tie rods and drag link. With a hunter Winn alighnment machine this would be able to be adjusted most of the bump steer out? Ok that's my thoughts, now people a lot smarter than me will you please chime in. Thanks chuck

I taught wheel alignment for 30-something years, as well as doing a lot of round track race car chassis building. One of the primary causes of bump steer in an independent suspension system is an error in the radius of the tie rods in comparison to the length of the lower control arms. All the relationships of suspension components and steering linkage need to form parallellograms. This includes the length of the Pitman arm and the idler arm, and the length of the relay rod between them. Once the position of the Pitman arm and the idler arm is established by locating the steering gear and the idler arm mount correctly, then the inner tie rod pivot needs to be located as close to the lower control arm pivot as possible. With the wheels pointed straight ahead, everything needs to be square- - - -Pitman arm and idler arm pointing straight ahead or back, and the inner tie rod pivot aligned with the control arm pivot. It also helps if the tie rods are approximately parallel to the ground at normal ride height. The idea is to have all the linkage as square as possible while driving straight down the road, and have as little change in angularity or radius when negotiating turns or bumps.
Jerry

This is my understanding also just trying to solve a problem that may occur later down the road. But don't believe to have a problem. Solve a problem if it arises. Thanks for the advice Jerry

So back to my question . If you make mistake and make drag link to short this will cause a problem with your linkage and cause bump steer. Before I finish this system I want advice? I can solve this problem easy now or a lot harder later? So by adding an adjustable drag link what do you think. My rock crawler has adjustable drag link to fine tune for different set ups and tire sizes

It's sort of a patch for something that should have been mocked up and built properly the first time. I would always lock a frame down tight to the floor on screw-adjustable jack stands with frame straightening chain anchors and assemble the suspension without any springs, then move the suspension up and down with a jack. I could spot errors in wheel alignment or positioning of tie rods, etc. before getting the vehicle out on the road or the race track.

Your main concern with bump steer is going to be changes in toe as the suspension cycles through its full range of travel. That's easy to measure if you don't put the springs on top of the lower control arms, or at least use VERY weak springs and cycle the suspension through its range of motion. There's no substitute for doing it right the first time.
Jerry

I have done this it all looks good. Maybe I have concern of some thing when there is nothing. .

I made a adjustable drag link you are suggesting so I could fine tune the steering box dead center adjustment. For mine, I used the modern style sealed tie-rod ends, one left, one right hand threaded. My uncle cut the threads for me on some sort of harder then normal steel rod. I was just going to use the center tie-rod rod and cut the right hand thread off, shorten the rod, and rethread it. Going that route, all I needed was a common right hand thread die.

Mine has come in handy for fine tuning the steering box. Changing leaf springs and lowering the front and rear threw off the center adjustment. It's very easy to dial in it right dead on, though it takes a couple of test drives and crawling under it in parking lots.

Joe