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Bump Steer?

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Trevor Jessie

Trevor Jessie

Yoda
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Breif history: I lowered my car and installed 340 lb springs. When I did this I had to reset my toe in. But I noticed that hitting bumps caused my car to jump to the side (rather widely). I switched back to my 3/4" sway bar from the 5/8", and now the problem is better, but still seems more pronounced than before. Other than the bump steering, the car is much better in the corners.

Question: Is there anything else I can try to reduce the bump steer? More toe-in? I really don't want to raise the car back up, because it is really sticking the corners well at this point. If I ever get my camera mount refined I'll post a video. BTW, this is a road car.
 
Bump steer in when the tie rod angle creates "funny steering". Usually because the car is lowered and the tie rod is less horizontal that it should be (it's never *perfectly* horizontal due to suspension up-and-down motion....generally, you want it as horizontal as possible while the car is driving down the road).

One way is to raise the rack. This involves shimming or re-engineering the rack mounts so that the rack is sitting "higher" in the chassis.

The other, more common solution, is to unscrew each tie rod end and replace it with a spherical rod end and acurately-sized long bolt that fits though the spherical end of the rod end. You will have to ream out the steering arm (where the taper is) so that the new bolt will fit though it. To alter the bump steer, you would add spacers between the spherical rod end and the steering arm.

Setting bump steer, in brief, involves removing the front springs, reassembling the front suspension, and jacking the car up and down while measuring the toe change. When toe change is at its minimum (as the car has been jacked through its full suspension motion), the bump steer is about right.

I'm sure you could get all this hardware from Hap Waldrop, another poster here at BCF. (look for acmespeedshop)

If you look in the roundy-round magazines (like "Circle Track") you'll see ads for fairly inexpensive bump steer gauges. It's fairly easy to build a bump steer setup too.

Your thicker sway bar may help simply because it stiffens suspension and limits up and down movement...sort of a band aid.
 
Thanks, I sort of thought that the sway bar was just masking the problem. Honestly, the car is not that low. I do not think it is bad enough to be unfafe. I don't like the idea of changing the steering arms/tie rod ends etc. I may try to get it on my fathers rack and do some measuring to see if shimming the rack is a possibility. It would be nice if someone had a CAD file for the front suspension so that I could work it out without getting dirty.
 
Trevor

Are you running poly bushings along with lowered springs?
BTDT and went back to rubber because the car would change lanes if you hit the white line in the middle.
I am currently running the same springs, rubber front end bushings and zero toe in. It has been perfect up til I hit a 12" sunken manhole in Staten Island 2 weeks ago.
I did something to the left shock and ripped the sway bar link from the car. I fixed the link but the shock is not as it used to be. Peter is sending me a set.
How are your shocks?
I also think I did other damage because something is going clunk every now and then. But even slightly weak shocks will make a big difference as I just found out.
 
No, no, no poly bushings. I had those in a mustang and they nearly drove me nuts on concrete expressways. I have rubber bushings and 1/16" toe in. The shocks were bought from Peter about two years ago I think. They seem to still be in very good working condition.
What are you using for a sway bar?
Tire size/ pressure?
I think I might drop the pressure in my front tires by a pound or two and see if I can tell any difference.
 
Not sure if this will help (or wether you have already done this) but one thing that reduced that problem for me while running an otherwise stock front suspension was the Timken bearing conversion. Didn't plan for it to reduce the shock through the wheels, it just happened that way. It was kind of a pain, and I had to face the back of the castle nuts a bit at a time and keep trying until I could get the correct(???) preload and line up with a hole for the pin. In the end I was very happy with it. I may still have part #s if you want them.
John
 
Bearings are on my list of preventive maintenance items, but right now, my current ones seem to be in good shape. Thanks for the suggestion.
 
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