Alignment question about self centering...confused

[bpu699]

Ok, a car self centers due to caster, correct? That's why if you release the steering wheel during a turn, the car straightens out... The steering rack itself, has no self centering effect... I think...

So what did I do wrong here...

Finished doing my alignment at home after adding adjustable camber plates. Camber set initially at 0 degrees. Caster equal bilaterally. Exact toe unknown, but has slight toe in. Car tracked perfectly straight but the steering wheel was slightly cocked to one side. Great, I thought. I was quite happy...

Looked at the tie rod ends, and one was screwed in a lot, while one was screwed in much less. So, rather than taking off the steering wheel, I just adjusted the tie rod ends two turns. Screwed one side in two turns, one side out two turns... So basically the toe stayed the same.

Great... Steering wheel perfectly straight now, but cars pull to the left...?!

Why? Camber, caster, toe didn't change. Does the steering rack have any centering effect??? If so, and I really don't think so, how would one know what the center is?

I would think that you could shift the tie rod end over 10 turns on each side, and as long as camber, caster, and toe didn't change...the car goes straight.... Though the steering wheel would then be very crooked...

Am I misunderstanding this?

Put another way, what causes a car with perfect camber and caster to go crooked? Assuming corner weights, for the sake of argument, aren't an issue. Playing devils advocate, if you had no toe in on the left, and 5 degrees toe in on the right.... Would the car go straight as it would self center at 2.5 degrees on each side, and the steering wheel would be crooked? Or, does the steering wheel stay straight with a wicked pull to the left?

Why?

Bo

[Trackrash]

The car will pull if the tie rods are not the same length on each side. If you have the steering wheel centered that should not be the problem.

Are you saying the steering wheel is actually pulling away from the center position or is the car just wanting to go in one direction?

Is the floor you used to check your camber PERFECTLY level? I have to use plywood on my garage floor to get it level. A small amount of slope, like 1/4" will have an affect on camber measurements.

Have you actually measured your caster? I'm guessing that is the issue. I have read that in the old days they would have more caster on one side of the car to counter the effect of the crown in the road.

[bpu699]

What puzzles me is that the car tracked straight up to the point I putzed with the tie rod ends... Caster and camber were measured and pretty spot on. Those weren't changed...

I would think that on a car that tracks straight, even if you subsequently royally screw up the toe in... It would still go straight. Your tires may not last long, but it will go straight.

I am pretty sure I can putz it back. . Just trying to understand why adjusting the tie rod ends as I did, caused a pull... The physics of it doesn't make sense...

Appreciate the help...

[ganun]

You know what they say, better to be lucky than.......
I'd say start by counting the turns on the steering wheel and centering the rack, then level the steering wheel on the splines, then set the toe. Keeping in mind what was said above, i.e. leveling, etc.
The track rods must be at the same angle and that is set by the same length left and right.
Castor works across, i.e. if the drivers side has more castor, the car will pull to right. A small tweak might be necessary to compensate for chassis age, wear, tolerances....

......

[Flieger]

There are many variables that determine the torque feedback to the steering wheel. At low speeds most self-centering is provided by the combination of steering axis inclination and spindle length. On our struts the SAI is directly related to camber (fixed offset). At higher speeds the trail (provided on 911s by caster angle) comes more into play.

I can tell you that with no other changes to my car, a corner balance fixed the pulling problem I had (I did not even align the car at the same time).

[chris_seven]

I don't believe track rod length differences side to side will make the car pull.

It will produce a tighter turning circle and one side of the car and unless the steering wheel has been removed and re-positioned it will produce an angular offset on the steering wheel when the car drives straight.

It used to be common practice that 'sloppy' shops made any track adjustments on one side of the car but this seems less common now.

If the track length differences are large then it could affect the self-centering

If there is an issue with the rear axle alignment which causes some thrust it may be corrected by using the thrust line as the reference to adjust toe. You need to check out all the rear geometry as well.

Also the caster being equal doesn't say enough - depending on the year of the car then 4 degrees positive would be a minimum and up to 7 degrees on early and SWB cars.


I would also check out the rack and all other joints for excessive stiction.

[bpu699]

Thanks guys... Plan to work on it again next weekend. Wish I had left "good enough" alone....

[stlrj]

This might be a good time to consider having an alignment performed at your local tire shop. I'm sure it would be obvious as soon as they got it on the rack.

Cheers,

Joe