Headers cause Bumpsteer - Help !

[Fastkarz]

mercgt73 - The bracket is solid. That 1/4" plate I put in with new bolts is rigid.

Injectedmav - Front 205/70R14 on 14" rims, 7.5" wide - approx 24.5" tall.
Rear G60-15 M/T Sportsmans on 15" rims - approx 26" tall.
I used Hedman Headers 88306 and they clear everything else ok.
I put a Drivers side motor mount BK602-1091 in last year with the new motor.

PaulS - I started working in a garage in 1986. BMW/MINI Master Certified. ASE A1-A8, X1, L1.
I think I can set an alignment if given the spec. Now automatic transmissions...thats a different story and I definately defer to you

Here are the specs I have and what I set the car to:
Spec is caster -1/2 +-2, i'm at +1 1/2
Spec is camber 1/4 +-1, i'm at +1/2
Spec is toe in 3/16 +- 1/8", i'm at 5/16"
I went with more camber because everyone is going for the shelby drop and more camber is the goal.
I set the caster more postive to help with directional stability on the highway. Thats what I was taught.

If zoomzoomguy is right it sounds like I have my caster at the wrong end of the range.

ThinK i should set it more on the negative side? Won't that just make this worse?
Thanks again for all the help/suggestions.
Sean

[mav1970]

Originally Posted by Fastkarz

Here are the specs I have and what I set the car to:
Spec is caster -1/2 +-2, i'm at +1 1/2
Spec is camber 1/4 +-1, i'm at +1/2
Spec is toe in 3/16 +- 1/8", i'm at 5/16"
I went with more camber because everyone is going for the shelby drop and more camber is the goal.
I set the caster more postive to help with directional stability on the highway. Thats what I was taught.

If zoomzoomguy is right it sounds like I have my caster at the wrong end of the range.

ThinK i should set it more on the negative side? Won't that just make this worse?
Thanks again for all the help/suggestions.
Sean

I used to set my own caster/camber when I was building stock cars and you always went positive on the caster. In racing it would only be 1 degree + on the left front and as much as 6 degrees + on the right front.

Just in my mind, anything negative I don't think of as caster at all. I look at a tool box being pushed down a garage floor and the 2 wheels that steer trail nicely behind their mounting point as in positive caster. Try to push it with the caster wheels held in the negative position - they always spin around to positive.

[injectedmav]

My camber is slightly negative at -.5° and I have a slight pull when I hit lines in the pavement or grooves that run in the direction of travel. It gets better when I tightened the ball socket preload spring in the valve and when I grease it, but it never goes away. I think that since the wheels tend to pull when the outside edge of the tire hits a section of pavement that is at a different plane than the other it tends to induce a camber pull and the entire assembly moves from the ball socket to the tie rods. My front end is very tight, the only give is in the valve ball socket and the angles are more aggressive than the ones you just posted. My caster is 2.5° pos and toe is about the same and I'm running a 245/50R16 tire. If you find a solution, I'd be happy to hear it. As I tighten everything up and get rid of the factory induced understeer I have noticed that problem has gotten more noticeable. I've just gotten used to driving it so I don't notice it as bad as when I change back from another vehicle.

[Fastkarz]

Mav1970 - So you agree with me and going positive with the caster should make it more stable.

Injectedmav - Going negative on the camber makes the car more squirly. I noticed a huge improvement in vehicle stability and reduced understeer once I had the front and rear sway bars in with positive Camber and postive Caster.

That said I still have the bumpsteer problem.

Thanks again for all the help/suggestions.
Sean

[mav1970]

Originally Posted by Fastkarz

Mav1970 - So you agree with me and going positive with the caster should make it more stable.

Absolutely

On your bumpsteer, if your steering cylinder is on a much different angle than your center link, and you hit a bump and compress your chassis, that cylinder, as it quickly swings up or down, will change length from it's point A to point B until it is level with your center link. Until it hits that level point it will either push or pull your center link to the right or left. Only for a quick moment but you would feel it. With stock cars, my bump steer situations were more at the length of the outer tie rod ends vs. the lower A-frame length from it's mount to the center of the lower ball joint being different. The same deal - bumpsteer is bumpsteer

[rthomas771]

Originally Posted by Fastkarz

Mav1970 - So you agree with me and going positive with the caster should make it more stable.

Injectedmav - Going negative on the camber makes the car more squirly. I noticed a huge improvement in vehicle stability and reduced understeer once I had the front and rear sway bars in with positive Camber and postive Caster.

That said I still have the bumpsteer problem.

Thanks again for all the help/suggestions.
Sean

What size sway bars?? If they are close to the same size then theres your problem. Remove the rear sway bar and see how it drives.

[mav1970]

Could you post a photo of what your cylinder looks like in relation to the rest of your steering while sitting?

Unless you can hang out under the bumper while at speed and take the picture

[mav1970]

Originally Posted by Fastkarz

I went with more camber because everyone is going for the shelby drop and more camber is the goal.

Your talking about a static camber setting

The Shelby drop actually gives your top A-frame a littlle head start in it's job to add camber "gain" as the car calls for it in a corner. I know my original top A-frames pointed down towards the ball joint so, if my car did a dive into a corner, my tops as they went through their arc, would have to get longer (adding positive camber) before they began to get shorter and begin to do their job recovering the camber actually lost in the cornering.

[Fastkarz]

You can see the drop down on the p/s ram to clear the headers. Centerlink is parallel to that cross member. Its a good 20-30 degree angle.

[mav1970]

Originally Posted by Fastkarz

You can see the drop down on the p/s ram to clear the headers. Centerlink is parallel to that cross member. Its a good 20-30 degree angle.

I can see the cylinder doing a bit of extra steering for you with that angle. Is it possible to do any fabricating on the drop bracket to lessen the angle? If you were able to maybe lower the entire car in the front that bracket would come down with the frame also. Is the hole on the center link tapered? If it wasn't you might be able to build some sort of drop bracket for the center link to level out the cylinder. I know having that cylinder hanging down that low isn't good either.

Just some thoughts