Alignment Question

[mbalbritton]

how does alignment change?

I'm not familiar with IFS alignment, so we'll stick to Solid axle in this question.

Thinking about how alignment is set and held, how would it come out of alignment? you either have a jam nut that (theoretically) keeps the drag link and tierod from spinning. Or you have the clamp deal. Assuming these don't come loose how would it change? Why would you need an alignment preformed?

[Jim_Lou]

In theory you don't, but in real life parts wear, chuckholes are hit, bolts loosen, springs sag and metal bends. Some cars hold alignment better than others, but you don't know if you have one of them until you check the alignment.

[bandhmo2]

On a solid front axles there is very little alignment drift.

Keep in mind that alignment consists of 3 major adjustments.

1. Toe in, or the amount the tires point toward each other. On a solid front axle this is about all that may need adjustment. It changes as tie rod ends, and ball joints wear on a solid axle. Usually set 0 to 0.5 degrees, pointing inward. Miss adjustment leads to poor tire wear and unpredictable steering. In extreme cases the tire develops a smeared look because the tires have to slide side ways as you move forward.

2. Camber is the angle of the tire side to side relative to vertical. On a solid axle it changes due to a bent tube or worn ball joints. Usually set around 0 degrees. Miss adjustment leads to tires wearing to one side.

3. Caster is the angle the king pin or ball joints make to the vertical in the front to back direction. On a solid front axle with leaf springs, it changes based on the springs, bent tubes, shackle lifts, axle wrap, and worn ball joints. Usually set around 3 to 8 degrees positive ( top ball joint behind the bottom). Caster helps your jeep track straight and your tires straighten out after a turn. Miss adjustment leads to poor tracking and unpredictable handling if lacking enough caster on both sides, or a steady pull to one side if caster is different side to side. The exact value of caster is not that big a deal provided it is more or less equal sided to side. When I worked in a alignment shop we would set about 1/4 degree more caster on the drivers side to pull back against the crown in the road.

As you can see, on a solid front axle there is very little to cause a change in alignment other then wear or abuse. Worn tie rod ends will show up as slop in the steering and be replaced long before damage to the tires results. Worn ball joints will change camber but this takes many miles and will result in a wear to the inside of the tires. Also on a solid front axle the ball joints only move when the steering is moved so there wear is very slow.

Caster will change as your springs sag, axles wrap, and ball joint wear, however (provided your ball joints wear evenly) it will do so evenly side to side causing no handling problems. About the only way to really screw up a Solid front axle is to bend it. This is not easy and usually requires jumping and the like.

The same reliability and strength can not be said for "independent" front ends, some are better then others. One of the worst of which is the Ford "twin Traction Beam" (TTB). The fact that this idea was put into production should be listed as one of the world wonders or prof that engineers are idiots (and I am an engineer). The fact that it was manufactured from 1980 to the late 90's is a sign that intelligent life may exist on this planet just not at Ford. This is literally an imposable to align the TTB. As the tires move up and down: Toe in, Camber, and Caster all change. So as the springs sag all 3 must be adjusted to get good tire wear and drive ability, not to mention the changes in ride hight due to load. After enough sag the adjustment busings in the ball joints can no longer be adjusted enough and the owner must chose between tire wear and pulling or a new set of springs.

In general a solid front axle will need alignment only after changing tie rod ends. Camber is set in the machining of the knuckles and tube end yokes. Caster will change as your springs wear but will be held the same side to side so you will likely not notice any problems. So short of bending a tube you should not need to align other then toe in.

Toe in can be set your self, by raising the front end and marking the tires. This is done by spinning the tire and holding a piece of chalk against it. then spin the tire and hold a pencil against it. this will create a sharp line in the chalk. if posible measure between these lines at the front and back of the tires. If this measurement can not be made due to stuff in the way, Use a plumb bob to transfer this line to the ground at the front and back of the tire. Measure between these points side to side, and figure the difference in distance front to back. About 1/32 to 1/8 shorter in front then in back and you are in good shape.

[mbalbritton]

so long story short... Wear and Tear. thanks

[n0nka]

bandhmo2,
thanks for the excellent tutorial.