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Steering..the included angle as a diagnostic angle..pos

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Hey guys my question pertains...
Hey guys my question pertains to steering angles. I am reading a textbook and the point of the chapter is using the included angle as a diagnostic angle. For example a car has pos camber so I subtract the camber from the included angle to obtain the SAI. So 1/2 pos cam minus 7 deg included angle equals 6&1/2 deg SAI. If the cam was neg 1/2 minus the 7 included angle gives a SAI of 7&1/2. They state rules SAI change without cam change means a bent strut/spindle. Determining which is wrong or bent part is the idea they are driving home. If SAI is wrong then the pivots ( either upper or lower ) are in the wrong location. What is that ? Bent components like the control arms? What they hit a curb, how does that look in reality ? The next thing they say is if the included angle isn t correct the strut or at least the spindle is bent and needs to be replacement. This is the ex that I don t understand. A) The camber range is 0 to 1 deg pos. The included angle spec is is 9. The cam read off the car is 3/4 neg deg. So the ideal cam is 1/2 making the SAI 8&1/2 deg. They say if the car hadthe 3/4 neg and the SAI was 8&1/2 the strut is bent. Why or how is the cam neg anyway? Is there a cross cam or am I wrong assuming the cam is adjustable. Now on the flip side if I calc SAI
then the included is 9&3/4 deg. Knowing this the strut isn t bent but the pivots moved changing the SAI then with it the camber. My question is how do I tell which is the right SAI ? the math adds correct please help meout
Submitted: 6 years ago.Category: Car
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8/5/2011
Auto Mechanic: Mike S., Mechanic replied 6 years ago
Mike S.
Mike S., Mechanic
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heavy_chevy_396 :

Steering axis inclination (SAI) and toe-out-on-turns are not adjustable angles and only used for checking for bent parts. Usually, if the steering axis inclination is off, either the upper or lower control arm is bent and possibly the spindle. It would depend on what the reading was, for example you could not usually cause a control arm to lengthen so if it was showing too much negative the top would be in too far and thus the upper control arm bent. Just the opposite for bottom or camber/included angle (SAI) too positive, then the bottom too far in or lower control arm bent. Not to mention it could possibly be the spindle also. If the toe-out-on-turn is off then the spindle is bent where the arm reaches out to hold the outer tie rod.

heavy_chevy_396 :

It all depends on how hard the curb is hit. Most of the time a simple camber/caster adjustment will bring it back within specs, if not something is bent too far. Everytime something is hit it bends, the adjustments are there to compensate for minor adjustments.

heavy_chevy_396 :

The strut technically in this case would be the same as the upper control arm since it won't have an upper control arm if there is a strut there.

heavy_chevy_396 :

If you ever looked at the upper and lower balljoints you would notice that they are nowhere close to being the same distance from the vehicle center. The camber is actually measuring the tire. The angle that the upper balljoint or in the case of a strut the spot where it connects and most likely different manufacturers have different ways of measuring would be the included angle, add or subtract from that the camber for SAI.

heavy_chevy_396 :

You asked, "Why or how is the cam neg anyway?" Answer, if the top gets bent in. Whether or not the upper control arm or strut.

heavy_chevy_396 :

Camber is adjustable on just about every vehicle as well as toe. Caster not all vehicles have an adjusment but wit the invention of aftermarket cam bolts, strut plates, etc they can be made adjustable.

heavy_chevy_396 :

What year, make,model engine are you working on? I will look up what specs I can.

Customer: My questions are coming right out of a steering suspension theory book. It was the idea that threw me off completely. They tell me me the car has.
Customer: My questions are straight out of a book example. The car in question has an included angle of 9 deg, the camber spec of 0 to 1 deg (stating this range means that the camber is adjustable, this is ok right?) they say it came in with 3/4 neg. You mentioned the fact that it's neg value exists is from an impact right? When you take the included value of 9 minus the pos camber say it's 1/2 deg you get 8&1/2 deg SAI. they say on the car with the neg camber reading you'll know the included angle is wrong ( bent strut ) that math is right so what is the proper SAI value?
heavy_chevy_396 :

The very first thing to do when checking alignments is checking parts for being worn or loose, checking tire air pressure, ride height. Different cars have different SAI specs.

heavy_chevy_396 :

For example here is the alignments specs for the 1970 Chevelle, note the different SAI specs. Also, what they call wheel pivot ratio is the same thing as toe-out-on-turn.

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Mike S.
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Auto Mechanic: Mike S., Mechanic replied 6 years ago

Thanks for the accept. Here's a tip for you. Here is how an instructor taught me years ago to do an alignment without a machine, just incase you wanted to know.

graphic

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Customer reply replied 6 years ago
Thank you for all your help
Auto Mechanic: Mike S., Mechanic replied 6 years ago
You are welcome!
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Customer reply replied 6 years ago
When you user the caster angle to correct road crown pull, which side of the front is usually more positive ? When I look at the car is it the side closest to the driver or is it the passenger side that gets the cross caster ?
Customer reply replied 6 years ago
When you user the caster angle to correct road crown pull, which side of the front is usually more positive ? When I look at the car is it the side closest to the driver or is it the passenger side that gets the cross caster ? I have read that it is the skill of the tech to choose the appropriate caster angle within allowable specs, have you ever opted not to have a cross caster ?
Auto Mechanic: Mike S., Mechanic replied 6 years ago
They both should be equal, but sometimes they do call for a slight pull to left. The vehicle will pull to the side with the least positive caster. Usually 1/2 degree will do it. So lets say the right front is 4 degrees positive caster then in order to make it pull slightly left to make up for the road crown you would want 3 1/2 degrees caster on the left front.
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Auto Mechanic: Mike S., Mechanic replied 6 years ago
What I always did was test drive the vehicle after the alignment and if it would travel 5-10 car lengths without changing lanes that was good enough for me. If it pulled slightly left I would say that is for road crown. If it pulled slightly right, I would say that is incase you fall alseep you crash harmlessly into the ditch or into a tree and not upcoming traffic.
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