by irock49 » Mon Jul 21, 2014 10:57 pm
The previous post brought up a couple of important issues to consider when installing a rack and pinion steering. The length of the tie rods and the length of the suspension arms have to be equal and parallel.
There was a discussion on a Mustang website that I follow, where someone asked how to check for bump steer. I posted the following, which includes some of the theory of suspension design. Hope it helps you.
"Here's how I'm planning the check for bump steer. You need a few items - a big piece of paper to tape to the garage floor, a bare wheel, a block to support the car at the normal height, a scissors jack, and a stiff plywood or Masonite board with a straight edge.
Let me explain the theory first. There are four pivot points whose locations determine the steering geometry. They are (A) the lower suspension arm pivot bolts, (B) the pivot point of the lower ball joint, (C) the pivot point of the tie rod end, and (D) the pivot point of the tie rod where it attaches to the steering rack. When viewed from the front of the car, these 4 points form a parallelogram. The theoretical line AB is parallel and equal length to CD, and AD is parallel and equal length to BC. As the suspension works up and down and the lower arm swings thru an arc. these lines should remain parallel to each other. If lines AB and CD are not the same length, they swing thru non-parallel arcs and the wheel either toes in or toes out depending on which line is longer.
To check for bump steer, place the front wheels in the neutral (straight ahead) position, jack up one side, remove the wheel and tire, and put a block under the frame to support the car at its normal height. Using the scissors jack under the lower suspension arm, raise it as high as it will go without lifting the car off the block. Put the bare wheel on the spindle, tape the paper to the garage floor, and hold the board against the bare wheel with the straight edge resting on the paper. Mark the line created by the intersection of the board and the paper. Lower the suspension arm in increments, maybe an inch at a time, and repeat the process of marking the line where the board meets the paper at each increment. If all the lines on the paper come out parallel, you don't have bump steer. If the lines angle outward, line CD is too long. If the lines angle inward, then CD is too short. "