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auto maintenance February 06, 2018

Scared Straight: A Lesson In Wheel Alignment

The automobile rose as a replacement for the centuries-old horse and wagon, and no nation needed personal transportation more than the infant United States.  Once we began to spread beyond the safe shelter of the eastern seaboard into the great wilderness beyond, a man simply could not hope to be anything without a horse and wagon.  And since he might find himself alone with his family hundreds of miles from anywhere, he had better be pretty handy at fixing the thing.  So it was natural that when Henry Ford’s “Tin Lizzy” displaced the horse and wagon, many men and women became accustomed to doing their own repairs and maintenance.  Heck, the Model T even came with a complete tool set.

Most people today realize that auto repairs need to be performed by trained certified technicians with proper equipment, yet there remains a sizable cult of street mechanics, and a belief that certain jobs that mostly involve bolting on parts can be safely relegated to them at a considerable savings.  If you believe this, ask yourself one question: Do you feel lucky?

A customer came in last week – and let me take this opportunity to say she was the kind of person who brightens up the world by her very presence. She needed a couple of tires and requested an alignment.  She seemed to know something wasn’t right on her vehicle so she was not surprised when we found bad tie rod ends in the pre-alignment check.  It was late in the day, so off she went in a Burke Centre Automotive loaner.

The next day I noticed her vehicle was on the alignment rack an inordinate amount of time.  Finally the tech brought me the repair order and the alignment report and asked me to test drive and give my opinion.  Even before I pulled out of the parking lot I noticed the vehicle seemed to turn way too easily.  I headed out to the Fairfax County Parkway to see how the vehicle tracked at road speed. I settled in at 55 mph and loosened my grip on the steering wheel to where I was just barely touching it.  No noticeable pull right or left. So far so good.

But roads are funny in the way they crown so water will run off them, so I went to switch to the left lane to see how it tracked there.  I applied just enough pressure on the steering wheel to gently drift the vehicle into the left lane. But that’s not what happened. The truck veered over so rapidly I had to correct back right to avoid going onto the shoulder, and then correct back left to avoid going back to the right lane. After confirming this several times I headed back to base and for the first time looked at the alignment report. The toe was well within specs and the camber was right on the edge but within spec, but the caster, which needed to be 5-6 degrees positive, was 4.5 degrees. NEGATIVE!

A brief lesson in over-simplified wheel alignment.  Toe is the most often adjusted and most critical angle.  Looking down at the front wheel from straight above, toe is the difference between the distance between the front of the front tires and the rear of the front tires.

Toe needs to be slightly inward, with the leading edge of the front tires closer than the trailing edges.  This is because, as the vehicle rolls forward, the forces of motion will tug the leading edges of the front tires out (away from each other), and toe needs to be almost neutral when driving, so a little toe-in will result in almost neutral toe when driving.  Toe always equalizes between right and left when in motion, so toe normally does not make a vehicle pull.  But it will lead to very accelerated tire wear on the inside or outside edges, and any significant amount of toe-out will result in a vehicle that is directionally unstable.

Camber is measured looking at the tires vertically from directly ahead.

If the tire leans inward, that’s negative camber.  If the tire leans outward, that’s positive camber.  Since you want all the tread of the tire contacting the surface of the road, camber is usually close to neutral. Camber problems will cause tire wear and pulling.  Both toe and camber can be seen or surmised with a trained eye, and determine how the tire contacts the road.

Caster cannot be seen visually on a car. It is determined by the relationship of suspension components to each other.

Caster is the pivot point of the wheel turning in relation to where it is being turned from, best visualized with these two examples.

Extreme positive caster:

The Motorcycle known as a Chopper, made famous by Peter Fonda in Easy Rider, is an exaggerated example of positive caster. That machine wants to go straight.  It does not want to turn. On a straight stretch of highway you could take a nap and wake up in your lane.  But it really doesn’t want to turn at all and may require an entire parking lot to do so.

Extreme negative caster:

The caster on a piece of furniture is an extreme example of negative caster. It easily swings any direction you want, but if you tried to push it down a narrow hall you would wind up hitting the walls on both sides because it turns too easily.  So manufacturers dial in enough positive caster to make your vehicle want to go straight and return to going straight without creating inordinate steering effort or distance.

On most vehicles caster does not go out of spec, and if it does, is a result of component wear on a high-mileage vehicle.  It does not cause tire wear but will cause a drift or pull if the right and left side are too different. It is not uncommon to find a vehicle where the caster is a few tenths of a degree up to a full degree out with no apparent consequence.

Back to my charming customer.  Our most experienced tech came to look at the vehicle and after a few minutes came back and said, “Doug, I think the upper control arms are on backwards” (right side on left side). I didn’t even think this was possible, but I told him to order one new with the side clearly marked and compare.  Indeed he spoke the truth. By reversing the control arms, the upper ball joint had been positioned further forward than it should have been, causing the negative caster.

After talking to the customer I found out that a fella who actually had quite a bit of mechanical experience (though not on passenger cars) had installed them at his house.  There aren’t many vehicles you could have made that mistake on, but there were some obvious clues a trained mechanic would have picked up on, but the most important thing is that our $25,000 alignment rack would certainly never have allowed us to miss that problem.

I sympathize with a hard-working person trying to put a little extra cash in their pocket, but the other side is, that vehicle was truly dangerous to drive. And had my customer had an emergency and had to swerve, she could quite easily have lost all control of the truck.  All is well now, but she drove a considerable period of time in an extremely unsafe situation.

Emergencies are emergencies. It’s Sunday morning, your battery is dead, and there’s no one to help you (for any amount of money). Go ahead and do what you have to do. But even putting a battery in or changing your own oil now has pitfalls.  A moment of reversed polarity because the guy at the store gave you a 24 battery instead of a 24F could destroy a $1,000 computer (it has happened).

Even the simple oil change is now booby-trapped. Plastic filter housings that break if you don’t have the exact tool for them are becoming quite popular. The day of the street mechanic has come to a close. Don’t find out the hard way.

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