The Stovebolt Site Forums The Shop Area Engine Shop Bump steer

I was just cruising thru the archives when I was distracted into an old thread about power steering. The writer was telling how the PS conversion on his TF caused too much bump steer. What is bump steer ? Need to know because I may have it, too.

Will take a stab at explaining but must warn that a teacher I'm not. Remember from your old math book that the shortest distance between two points is a straight line? When your wheels are aimed straight ahead the rod between the pitman arm and steering arm (the draglink) is horizontal and level---providing there's been no dropping, jacking up, etc. Now if you hit a bump the axle goes up so the distance between the pitman arm and the steering arm increases but the steel draglink doesn't stretch so your wheel turns as the steering arm is forced to maintain that distance, thus the bump caused the wheel to turn or "steer". A draglink is really dumb so it it the same length (or longer) and in the same position (level) then it doesn't know whether it's hooked to a manual or power steering box. I have an idea that the increased quickness of the power unit made the truck bobble more rather than an increase in bump steer.

Power steering will not cause "more bumpsteer", as bumpsteer is caused more by bad steering/suspension geometry that anything.

Bumpsteer happens when front suspension movement up or down causes the front wheels to deflect (i.e. they steer) which you'll need to correct with the steering wheel every time you go over any bump which causes the suspension to move. If you have bad bumpsteer the truck will be no fun to drive.

On our trucks with a straight axles and a steering box, bump steer is usually caused when someone has jacked or dropped the suspension which will cause the drag link not to be parallel to the ground when your truck is parked at the roadside.

If the draglink makes a big angle up or down at your normal ride height it will cause very noticeable bump steer every time the suspension moves; the cure is to remount the steering box so that the draglink is again parallel to the ground at normal ride height, just like it was with the stock setup.

Stuart.

Thanks, guys. When you put things in geometric terms, it makes perfect sense. I definitely have bump steer. The drag link is probably 15 to 20 degrees from horizontal. I'll add that to my list of things to do.