Recently I have noticed an increase of forum members with questions and concerns regarding suspension parts and alignments. A large portion of handling issues like a left or right hand pull, wandering, squeeks, rattles, clunks, and shaking have to do with one or more suspension parts being worn to the point of either having play outside of a specified tolerance or to complete falure. I'll be covering all of the methods used to inspect your front end parts and well as what to look for in regards to play and what is considered acceptable or not. I do not claim to know everything about all suspension systems. I am an ASE suspension and steering certified alignment tech with about 7 years experience, so while I haven't done this as long as some, I feel I have above average knowledge of the subject. Some images posted are ones I've taken myself, while others are from a general search as I have either lack of examples at my disposal or lack of time to make a diagram.
First I'll cover alignment fundamentals and how certain measurements and settings effect handling.
Camber angle is the measure in degrees of the difference between the wheel's vertical alignment perpendicular to the surface. Negative camber being that the top of the tire is leaning inward toward the engine and positive when leaning outward from the engine. Negative camber is becoming increasingly more popular because of its visual appeal. The real advantages to negative camber are seen in the handling characteristics. Zero camber results in more even wear across the tread of a tire. Positive Camber is most often used on offroad and agricultural vehicles due to it providing a lower steering effort.
Caster is harder for most to understand, but is defined as the angle created by the pivot point of the steering from the front to back of the vehicle. Caster is positive if the line is angled forward and negative if angled backward. Positive caster will result in more stability at higher speeds and faster return of the steering wheel to level, but will increase tire lean while cornering as well as increase steering effort. Most road vehicles will have Cross-Caster, which means there is a difference in the caster angle on each side of the vehicle. (Example: 3.0 degrees on one side and 3.5 degrees on the other) This is actually a safety feature to cause un-manned vehicles or drivers who lose steering control to drift away from instead of into oncoming traffic. However, generally vehicles are set to drive as straight as possible, which often requires a cross-caster split of about half of a degree to compensate for crown in the road, always more positive on the passenger side. (Example- 3.0 Degrees on the diver's side and 3.5 degrees on the passenger side)
This is the easieast to vizualize. This is the angle which the tires are pointing when viewed from the top down. Toe is the biggest factor in how your tires wear. If the tires are pointed inward or outward, they will scrub against the surface of the road and cause wear along the edges. But sometimes tread life can be sacrificed for performance or stability. Positive toe will provide straighter driving characteristics at the cost of turning ability. This is found mostly in rear wheel drive vehicles. At speed, the tires will straighten out, helping to reduce excessive tire wear. Front wheel drive vehicles often have negative toe for the opposite reason. Their suspension arms pull slightly inward, so a slight negative toe will compensate for the drag and level out the wheels at speed as well as increases cornering ability. This sacrifices straight line stability though.
Everyone has a different way to check certain things. This is how I do my inspections at work. The pictures shown are of a 1994 2WD Blazer.*
After getting the vehicle racked and at working height, I first check all bushings for cracking or tears. Minor cracking like what is shown on these swaybar end links and mount bushings, isn't of much concern. More severe cracking or tears would warrant replacement.
These control arm bushings on the other hand, are due for replacement, even though no abnormal movement is found.
Next, lift the vehicle by both control arms and make sure its stable. While grasping the tire by the top and bottom (red arrows), shake the wheel by pushing and pulling on alternating hands. Try to effect the camber. You may feel a slight amount of play in the wheel bearings. Very slight play is normal for S-series trucks without hub assemblies (S10, Sonoma). Vehicles with hub assemblies should have zero play (Blazer, Jimmy). Bad ball joints or upper control arm bushings may also be found doing this. Next grab the tire on each side (blue arrows) and use the same alternating force. This is used to find play in the center link, idler/pitman arms, and inner/outter tie rod ends. Ball joints can be checked for vertical play by placing a pry bar under the tire and ground and prying upward with moderate force. Any play warrants replacement.
Labeled in this picture are the tie rod ends (2&3 at the center link, 5&6 are attached at the spindle), Pitman arm (4), and Idler arm (1). Any movement other than twisting of the ball type joints (which under normal driving will be minimal) is considered excessive play. 2WD vehicles have a non wear pitman arm. If play is found here, the center link must be replaced.
Here is the before and after of an alignment I did earlier today on a 1997+ 4WD Jimmy. The after specs are what you are looking for in a quality alignment. This vehicle drove straight with no pull, wandering, or any other symptom.
I hope this helps clear up some of the confusion/questions regarding checking parts and what alignment terms are and how they effect each other. Feel free to ask any questions I left unanswered and I'll try my best to answer them.