Steering and Alignment Questions (W124,201,126) - PeachParts Mercedes-Benz Forum

JamesDean · #1 10-02-2013, 08:48 AM

Good Morning All,

I have a few questions regarding the steering and alignment on these cars.

1) How does the steering geometry compensate for road crown?

As long as the crown is not ridiculous, should my car always drive straight down with minimal compensation needed from the the driver? Or should I expect to have to hold the wheel in a certain direction based on the lane I am in?

Example: In my 124, if I am in the right most lane on the freeway, I can drive with minimal corrections needed to the wheel. If I go into the middle or right most lanes, I need to hold the wheel to the right otherwise it will pull to the left.

2) How does a high or low set caster effect the steering?

Does a low caster make the car tramline or follow the road imperfections/variations more? Or is this completely unrelated? If the car has a high caster value set, does that make the wheels "desire" to return to center higher thus "listening" to the steering wheel over the road surface variations?

As I understand it, using the steering gear box locking pin (removing the drain bolt, and installing a longer one that goes into the gear box piston is crucial as well as the use of a spreader bar in preloading the suspension. These are the first two steps in a proper alignment, correct?

3) In general, when the car is getting aligned, what effect does leaving the steering gear box centering pin out have on the overall alignment?

If someone were to align the car, centering the wheel by locking it using the normal steering lock that engaged when you take your key out and move the wheel about...what effect would that have on steering? Would that "position" be center?

[B] 4) In general, when the car is getting aligned, what effect does NOT using the spreader bar have?

Just trying to sort things out and clear them up! Thanks for the replies and comments!

pmckechnie · #2 10-04-2013, 12:03 PM

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

Duke2.6 · #3 10-04-2013, 01:32 PM

I haven't been in an alignment shop for over 30 years. I align all my cars with an inclinometer and tape measure. Alignment shops have wonderful equipment, but few of the techs really understand how it works and don't understand suspension geometry.

There are probably still shops that want to set camber or caster "lead" to compensate for road crown. Such advise dates from the 1920s when most roads were unpaved and highly crowned to promote rapid drainage. Modern paved roads have very little crown and don't need any "lead" in the aligment settings. Set everything as close to equal on both side as can be achieved within the accuracy of adjustments and measurements.

All my cars are set for maximum positive caster and maximum negative camber, EQUAL ON BOTH SIDES within the available adjustment range. This means that on a typical road that is cambered for drainage, they will usually drift VERY SLOWLY to the right. So if you fall asleep on a two lane road you won't drift into the oncoming lane and have a head on collision.

In the left lane(s) of an interstate, this might mean the car will drift left, but interstates typically have center barriers or wide median strips.

On my '88 190E 2.6 I was able to achieve +10.5 deg. caster and -0.75 deg. camber. These settings minimize understeer, which is greater on the front heavy 2.6 compared to the 2.3. The front weight distributions are 57/53 percent, respectively.

High positive caster promotes straight line stability and high self centering torque, but it can also cause shimmy, which is why Mercs have a front steering damper, and I can assure you that when this damper fails the front end can go into a violent shimmy, the likes of which I have never experienced in any car. High caster settings also generally require power steering because of the high self-centering torque, which would make for very high steering effort on a manual steering car. With manual steering 2-3 degrees positive caster is about the limit before effort becomes excessive.

High postive caster also yields negative camber gain on the outside front tire when you turn, and the combination of a little static negative camber and the negative camber gain compensates for body roll and keeps the outside front tire closer to vertical with the road. This is why my settings reduce understeer, but they do no cause excessive inside front tire wear.

I didn't use a spreader bar to set the toe, but merely set it about about 1/16" toe in. If the tie rods measure equal length the steering wheel should be centered when the car is going straight, but I usually have to tweak one tie rod once or twice to get the steering wheel dead centered, as even the slightlest off-center of the steering wheel when driving straight drives me nuts.

Duke

slk230red · #4 10-04-2013, 02:47 PM

Here's an interesting DIY.......

Mercedes DIY Alignment