Thought this be a slam dunk...Dodge Omni rear steer rack fitted to a 54 Hudson Jet drag car...no street duty with rear steer spindles...the lower arm arms are much longer than most I've seen and angled to the rear...not parallel to frame...is this the problem...bump steer is Bad...ball joints on steering...top or flipped to bottom bottom is worse.Cant raise rack,could lower or move front or rear ward...is there any hope here or change to straight axle....thanks !
For starters, are all the bushings and ball joints tight, like new condition? If not replace everything. Some basics. An imaginary line from upper A arm pivot to lower A arm pivot. The outer tie rod pivot on the rack should be on the line described above. Are you close?
We can see from the picture that the inner tie rod end is about halfway along the lower arm. The tie rod and lower arm travel in very different arcs, and you will not be able to get rid of the bump steer unless you can get the inner tie rod end to be along the line he mentioned, but also along a line from front to rear inner lower arm pivots. there are racks from some fwd cars that have the inner tie rod ends close to the center, that might work, but it would be so much more HAMBish to use a normal steering box instead. And you might as well throw a straight axle under there, while you're at it.
Quick eye ball, that is a pretty big mismatch. The work needed to make it not scary, probably easier to grab a R&P out of a Cavalier.
Basically what pprather said... A line between the inner, upper arm pivot, the lower, inner arm pivot, AND the inner pivot of the R&P is what the lengths SHOULD BE...! All three of these pivot points NEED to be on the same line to keep the bump steer in check. The farther away they are, the worse the bump steer will be. Height wise, the R&P can be anywhere...BUT still needs to have its inner pivot aligned with the control arms pivot. All three of the pivot points NEED...to move smoothly (as in NO binding, when having different pivot points) up and down, not only to keep the bump steer in check, but ALSO to minimize the wear and tear of the steering components. Check out any automotive suspension book...learn... Mike
Based on the pictures, if its possible to move your current rack forward on the frame, to near the crossmember? Then you can add to the length of each sides tie rod, you may be able to get close enough to eliminate most of your bump steer. If you can get the length of the tie rods to equal (or as close as possible) to the length of the lower control arm, your bump steer should improve. I don't think that is possible with the rack's current position. With the rack in its current position, I don't believe the Cavalier rack would work either. The Cavalier rack's center pivots move left to right as the steering moves left to right, so even if the length of the tie rods are close to the correct length, they are only close to being correct when the steering is straight, and will be farther off then it currently is when the wheels reach full left or right lock which could make a really funky bump steer on a curve or turn. The Cavalier rack would work well if you could use the vehicle's original tie rod and center link assembly and attach the center link to the Cavalier's center steering pivot point. You would have to get the cavalier rack close enough for the original center link to keep its original position on the car.
Here is a very basic idea of what they are saying. https://suspensionsecrets.co.uk/bump-steer/ There are a ton of articles out there if you avoid the local library, but there are a lot of books to get into also. Short and sweet, that rack is never going to work, and the angles of motion on the lower control arms aren't going to work with any rack alone. Look at the lower arm pivot and the tire rod in the first drawing here. Note the bell crank for the tie rod. https://www.hudsonjet.hetclub.org/hudsonjetfrontsus.html
here's a modified version of that drawing, showing both sides of the car. The top ends of the orange lines are where the inner tie rod ends want to be (in this plane). You also have to look at it from the front of the car, and make sure the arcs of the tie rods and lower control arms match reasonably well as the suspension moves through it's up and down travel. one thing about bump steer, is that if you have really long tie rods, they can tolerate a lot more error, as long as the tie rod is mostly parallel to the lower control arm, at rest. Short tie rods like you have now, really make the problem worse. yes, I put a rack on a 1930s IFS many years ago, and learned a few things! I ended up removing it
I agree with all of the above about geometry. No way to make it work that I'm aware off. Changing pivot points usually causes problems.
I said "and the angles of motion on the lower control arms aren't going to work with any rack alone." You could devise a way to connect a rack to the bell crank, but 1. that is going to negate the point of changing to a rack instead of a box, except for smoothness and feel, which is going to be lost somewhat using the bell crank and tie rods and 2. will require some serious packaging work, which requires knowing all the geometry needed and mounting a modern rack to the OE steering mechanism. You say it's a drag car, no street duty. Choices to my mind are in order Cheap and easy to Hard Go back to OE steering box. Replace OE box with another box that works with the center steer. Go complete straight axle on leaf springs and steering box. Probably requires front frame stubs/replacement. https://www.speedwaymotors.com/Gass...e-and-Brake-Kits-52-1-4-Hub-to-Hub,25490.html note this does not include steering or frame work Go complete straight axle on coil springs and steering box. Probably requires front frame stubs/replacement. Go complete A arm drag front end with rack. Requires front frame stubs/replacement. https://www.cachassisworks.com/p-15...ont-frame-clip-and-suspension-custom-fit.html Stay with OE suspension and engineer a rack into OE steering.
That setup will never work with the geometry of the lower control arms in relation to the rack's inner tie rods (inside the rubber boot) as stated above. I'd remove it and find something a bit more complimentary to the existing suspension if that's what you want. Otherwise you have quite a bit of reengineering to do to make it correct.
Uprights ball joints and outer tierod balljoint need to sweep in the same congruent arcs in useful suspension travel to minimize bumpsteer. Links can be at all sorts of funky angles, not neccesarily parallel to effectively work. As long as the control arms and tierod links dont induce unwanted steer angles Not sure what you mean. Is this a comment regarding the Cavalier rack in this particular frame? Because no matter which car & rack, the steering links move left or right when steering and do not change length or cause bumpsteer themselves. Only when the sweeping arcs are not congruent. The beauty of the Cavi rack is since its inner mounts are so close to each other one can cusomize nearly any link length desired. MII style racks you are limited to the racks physical length. Positioning is limited to input shaft location clearance and the external diemensions of the rack itself.
Yes, it would be for this frame, but may also apply to any frame the Cavalier rack it attached to. The original car had a center link and two tie rods that were the same length as the lower control arm. The center mounting points on a Cavalier rack are 4" apart, and they have two very long tie rods. If the rack can be placed in a position where the line drawn through the lower control arm mounting points can be placed so that the center pins are on that correct line, the bump steer will likely not be present. But, the control arm and the tie rod both still have to have the same arch. The control arms would have to be at a pretty sharp angle for the center pins to get the rack correctly located. If the location is incorrect, the arches will be incorrect and the bump steer will likely still be present.
The Jalopy Journal
