First, if you ask 10 alignment people these questions, you will get 30 answers. From what I understand, caster, and/or toe both effect how a car responds to the crown in a road. You can have the car completely un-effected by the crown but then the steerinng will not be as sensitive in normal driving. I have come to the conclusion that is why there is a range in each of the adjustments. When you are looking for an alignment shop, use the oldest alignment tech with the most years experience you can fine. In other words, someone who understands what each alignment does and which will be best for your driving style.

I have been paying attention to my 500 SEL and have realized it is affected by the crown in the road. On flat roads (Interstate) is goes straight. On crowned roads it wants to go up the crown, pulls left in the right lane and pulls right on the left lane. I guess I am just accustomed to it and I don't notice it in day to day driving. My steering is very sinsitive and responsive and that is the way I like it.

As far as the centering pin(bolt) in the steering box, it is the first step in the aignment. If nothing has been changed. then locking the steering wheel in the straight ahead position is fine. Every thing in the steering system is aligned to the steering box. If, for instance the steering wheel had been removed and turned to set it straight when the car is going straight but the wheeel was off because of a steering column to steering box coupling was replaced incorrectly then every thing will be off if the car is aligned to the steering wheel. Also the turn signals will not cancel correctly because the steering column will not be aligned correctly. The steering box will not be centered. The idler arm will not be centered. Get the idea? Every thing needs to be adjusted to the steering box, not to the steering wheel. So, lock the steering box, make sure the steering lock locks in that position, steering wheel straight, and wheels aligned last.
The purpose of the spreader bar is to take out any play in the system that will affect the toe adjustment. As the car goes down the road, the front wheels are pushed back because of frictioon and rolling resistance. It doesn't make any difference at low speed, but 70+ mph it can make a big difference and affect how the car drives.

So, find an alignment tech that understands alignment, not just the alignment machine he is using, and tell him what you expect from the car and ask what you should expect from the car. Ask specific questions like "What will the car do on a crowned road and how will it affect sensitivity." If he can't answer your questions then find some one else.

I hope some of this can help you understand why the steering lock tools is important and what the spreader bar does, and that every car is going to drive different and needs to be aligned to the proferences of the driver. , and there are no definitive answers when it comes to 30 year old cars that were designed to run both on 30 mph streets and 150 mph 'Interstate' highways in Germany.

Paul

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84 500 SEL (307,xxx miles)