w115 alinment disaster - Page 2 - PeachParts Mercedes-Benz Forum

Gurunutkins · #16 01-06-2009, 09:05 AM

Read this article, it should give you the basics

http://autorepair.about.com/od/glossary/ss/df_alignment.htm
cheers
barri

Tomguy · #17 01-06-2009, 02:07 PM

Just to clarify because I think this is part of the confusion: A minute is a fraction of a degree. Toe, Camber, Caster (etc) are measured by pros in terms of degrees. To measure one yourself (IE Toe) you would have a straight line parallel to your car, the toe in or out would be the line such as:
| (car)
\ (tire)
|\ toe angle is the angle between the two lines in degrees, minutes, seconds (IE 2° 5' 43")

todds · #18 01-07-2009, 01:46 PM

I've never attempted an alignment on my Benzes because, to be honest, they've never needed it. After repairing the steering coupling on my 67 it's straight and true as anyone could want, the w201's perfect too. I had an Alfa and a couple Cadillacs I used to fiddle with and learned through much trial and error. Many things I initially blamed on alignment were actually stuff like bushings and former accident/curb damage. The strangest thing I noticed which effected one Cadillac specifically was motor mounts, they made the car feel totally unwieldy through turns. I suppose a 7 liter motor flopping around will do that. All that said, if it was you that messed up the alignment and it was relatively fine beforehand then I think you ought to be able to get it back close enough to at least get you to a competent shop safely. Remember that there are rear wheels too and if those are off it'll throw everything else out of whack.

I know that there has been mention of a torque bar that attaches to the front wheels in order to replicate the force pushing the tires out while driving. Some of the specs for toe would take into account using this bar, while others wouldn't. The idea of a little toe-in is that it'll be at zero when the car is in motion with the wheels being pushed out by the road. Achieving this zero toe while driving is good for gas mileage and tire wear. More toe-in might "feel" a little better at the wheel, but will also wear out the wheels and conversely toe-OUT will feel completely miserable. Whether you use the torque-bar to spread the wheels and set to zero, or use a slightly toed-in spec without the bar, or use a dynamic balancing available at some shops with a zero spec the end result is the same.

Once you get into caster and camber you're throwing all kinds of different variables into the mix and better know what you're doing. Caster is like the wheels on a shopping cart or a motorcycle. Either they're going to drag behind the suspension a little bit or lead in front of it. Dragging behind is preferable and tends to mitigate any wandering (positive caster)

Related to that is also Steering Axis Inclination, SAI, which is non-adjustable usually. Some cars have a negative caster spec because they have tons of SAI. It acts just like caster except across the center of the car horizontally instead of front-to-back. The weight of the engine and front end is used to help center the steering with SAI. My Caddies were like this.

Personally I prefer the Benz approach of tons of positive caster and having a zero-offset. You can see this when the car is parked and the wheels are cranked all the way to the lock, they tend to lay way over to the side and it will almost look like something is wrong.

The way you measure both of those things is with a camber tool which is like a fancy carpenter's level that attaches to the wheel. The camber is measured with steering on center and the castor is measured at a certain degree of steering (I think it was 20 degrees on my car at the time) causing the wheels to lean over as described above. Some cars have very slightly different camber L to R to correct for road crown, however it is very little, like a quarter degree. If the camber isn't right the car will pull to one side. I'm not sure if Benz does this or not, perhaps the huge caster spec takes care of it.

You can set toe fairly accurately using strings or a bar with pointers and tape or white out while rolling the car forward. However if you play around by yourself just be reticent of that fact when you do drive your car, you shouldn't charge into hairpin corners or attempt high speeds until you're certain everything is as it is supposed to be. If you drive long term with your alignment way off it can be hard on the steering, bushings and tires as well as your psyche ;-)

pixelsblack009 · #19 01-08-2009, 04:25 AM

well thanks for all the posts guys my car each time i get it aligned the two front wheels are popping out allot (toe out i assume) is this incorrect also i still have a few doubts about the degrees and minute thing can someone give me an example or so i cant quite understand the whole thing

Gurunutkins · #20 01-08-2009, 09:23 AM

Hi pixelsblack009

the degrees and minutes thing is just like yards, feet and inches (or if you are not american meters, centimeters and millimeters) just like there are 3 feet in a yard (or 100cm in a meter) so there are 60 minutes in a degree so each minute is 1/60th of a degree. and similarly just like there are 12 inches in a foot (or 10mm in a cm) there are 60 seconds in each minute. So if you are told to set an angle at 3 deg 15 minutes and 15 seconds then you are looking at 3 deg plus 15/60th's of a degree plus 15/60th's of a minuteas 15/60th's of a degree is a 1/4 degree you have 3.25 degrees plus 15/60th's of a minute. 15/60th's of a minute is a 1/4 of a minute so what you have overall is 3.275 deg

.

On your car there should be no toe out they should point slightly together at the front by about 1.5 to 3 deg or 3 to 5mm, a lot of this is done by feel when driving but nearly all cars anywhere have toe in not toe out.

The camber which is how much the wheel leans in at the top should be almost zero and you should not mess with this unless you really know what you are doing as it requires you to move the obcentric bolts on the suspension mounts

.

I wont get into caster at all, just leave it alone or go to a really good alignment store.

If you have continual toe out even after it has been set correctly then you probably have some other problem with the suspension or steering and you need to keep checking to see what the fault is (play in the inner or outer tie rods etc). also make sure whoever is doing the work is doing it with the car firmly on the ground and is not lifting the front to make ajustments then putting it down again to remeasure without rolling the car to settle the wheels (I know it wont happen with a dedicated alignment shop but Ive seen it happen elswhere in the world with shade tree mechanics and you dont say where you are)

good luck
Barri

meltedpanda · #21 01-09-2009, 06:20 PM

been out of pocket for awhile, but it seems like the guys/gals have you pointed in the right direction
Ron

pixelsblack009 · #22 01-11-2009, 12:34 AM

ok well i get a better idea of the minute thing also i know the terms because for over a weak i have been reading so many articles and here in srilanka there are no good stores just stupid ones that tell you the same thing over and over and in a month your tires are all balled they think its correct to have the wheels poping way out thanks every one i'm going home to try it out now (15 years old)