|
|
 |
Proper wheel alignment is important for three reasons: (1) efficient steering, (2) good directional stability, and (3) optimal tire wear. In other words, when the front end of a vehicle is properly aligned, the tires will wear in a normal manner; the vehicle will track in a straight line, more or less; and the vehicle will steer easily. If the front end is out of whack, all bets are off.
Advancements in alignment equipment have greatly enhanced the accuracy of alignment work, but it’s still important to understand the hows and whys of the different alignment angles in order to perform the most accurate alignment job possible. With this in mind, we’ll review alignment basics this month and give you some tips to help you with alignment work.
Camber, Caster and Toe
When discussing wheel alignment parameters,seven angles are mentioned: (1) camber, (2) caster,(3) toe, (4) toe-out on turns, (5) steering axisinclination, (6) included angle, and (7) thrust angle. Of these seven angles, all of which can be measured, only three are adjusted when a front end alignment is done — camber, caster and toe. In many cases on late model cars, caster is non-adjustable. Furthermore, on vehicles such as the late model minivans, the camber and caster were set at the time the vehicle was designed and according to the location of the suspension components, so they do not require adjustment. This is known as net build. Regardless of the design of the vehicle, camber, caster and toe should be measured and — on the appropriate vehicles — adjusted, as necessary.
Camber is the inward (negative) or outward (positive) tilt of the top of the tire and wheel assembly, as viewed from the front of the vehicle. It is measured in degrees of an angle relative to a true vertical line. Camber is a tire wearing angle. Excessive negative camber will cause abnormal tread wear on the inside of the tire, while excessive positive camber will cause abnormal tire wear on the outside of the tire.
Caster is the forward (negative) or rearward (positive) tilt of the steering knuckle as viewed from the side of the vehicle. It is measured in degrees of an angle relative to a true vertical line. Caster is not a tire wearing angle; however, a difference in caster between the front wheels can cause the vehicle to lead to the side with the least positive caster.
Toe is the inward or outward angle of the wheels as viewed from the top of the vehicle. Toe is illustrated in Figure 1. Toe-in indicates that the front edges of the wheels are closer together than the rear edges. Conversely, toe-out indicates the opposite: the rear edges of the wheels are closer together than the front edges. Toe is a tire wearing angle.
Pre-Wheel Alignment Inspection
The inspection performed prior to checking and adjusting the wheel alignment angles is as important as the alignment procedure itself. Failure to detect and repair any problems that will negatively impact the accuracy of the alignment will result in wheel alignment angle measurements that are inaccurate and a vehicle that is not properly aligned. Perform the inspection routine listed below before beginning the alignment:
1. Verify that the fuel tank is full. A tank that is less than full will change the ride height of the vehicle.
2. Remove any items from the passenger compartment and trunk that are not factory equipment.
3. Check the tires. All tires should be the same size and in good condition. Each should show about the same amount of wear. Inflate all four tires to the recommended air pressure.
4. Check the front wheel and tire assemblies for excessive radial runout.
5. Inspect the lower ball joints and all steering linkages, especially outer tie rod ends, for excessive play, binding, wear or damage. Replace any components that are bad. Remember, worn outer tie rod ends are a major cause of abnormal tire wear, as toe cannot be accurately set when these components are worn.
6. Check the suspension fasteners to be sure these parts are properly torqued, and tighten any loose fasteners.
7. Inspect all suspension component bushings. Look for signs of wear and/or deterioration, and replace any bad bushings.
8. Check the ride height of the vehicle (specifications are listed in the appropriate service manual). If the ride height is not within specifications, check for excessive weight in the vehicle, one or more worn or broken coil spring(s), and tire size.
Performing the Wheel Alignment
Now it’s time to do the wheel alignment. First, position the vehicle on the alignment rack and install all the required alignment equipment (always follow the alignment equipment manufacturer’s instructions). Next, jounce the rear of the vehicle, then the front in that order. Push down on the center of the bumper and release the bumper at the bottom of the jounce cycle. Jounce each end of the vehicle an equalnumber of times.
Read the front and rear alignment settings. Compare the current settings with the specifications for camber, caster and toe that are listed in the appropriate service manual. If camber and caster are within specs, you can proceed to adjusting toe, if required. If camber and/or caster are not within specs, you have to look at your options.
As mentioned earlier, camber and caster might not be adjustable on the vehicle that you are servicing. However, a camber adjustment bolt package is available for certain vehicles, such as the late model minivans. If caster is not within specs, there’s really nothing that can be done. It should be noted, though, that all the suspension components should be inspected for any signs of damage or bending if these two alignment angles are out of spec. If such damage is found, it’s the likely source of the alignment problem.
Installing the Camber Adjustment Bolt Package, and performing the required component modifications allows camber adjustment. On some vehicles, the lower strut-to-steering knuckle attaching bolt hole on the strut clevis bracket is elongated (see Figure 2). A special cam bolt is installed to replace the original flange bolt. Rotating this cam bolt changes the camber angle, as the cam turns against the clevis bracket cam stop areas.
On other vehicles, the strut clevis bracket is not slotted. The Camber Adjustment Bolt Package is a set of slightly undersized bolts that can be used in place of the original lower strut-to-knuckle attaching bolts. These undersized bolts allow for some inward and outward movement of the top of the knuckle providing camber adjustment.
After any camber and caster issues have been settled, you can take care of adjusting the toe. It’s likely that some toe adjustment will have to be made, as normal day-to-day driving has a tendency to knock the setting out of spec. With that in mind, let’s review the basics for adjusting toe (use Figure 3 as a reference).
First, center the steering wheel and lock it in place. Second, remove the clamps on the outer end of the inner tie rod boots. This will prevent the boot from twisting when the inner tie rod end is rotated to set the toe. Next, loosen the front inner-to-outer tie rod end jam nuts. Then, rotate the inner tie rod ends by grasping the inner ends on the serrations to set the toe to specifications. Finally, tighten the jam nuts and reinstall the outer boot clamps.
After the wheel alignment is completed, remove the alignment equipment, drive the vehicle off the alignment rack, and take the vehicle for a test drive. Note any wandering, drifting or pulling that would indicate that the alignment is still out-of-spec. Also, check to be sure that any problems reported by the vehicle owner have been corrected.
|
|
