For a vehicle to steer straight and handle safely, wheel alignment needs to be within certain specifications. When a vehicle is in the service bay, technicians need to take the time to make sure the vehicle still has the proper toe, camber and caster angle settings. In addition to handling and safety issues, a properly aligned vehicle would extend the life of the tyres.
Unfortunately, not all of the vehicles are easy to align. According to one alignment equipment manufacturer, 32 per cent of vehicles on the road today require rear shims for camber and toe adjustment. Shops that choose not to work on these hard-to-align vehicles are not only losing the immediate business, but by sending the customer down the road to a competitor, may be losing the customer for good.
To help cure these vehicles’ alignment problems, there are aftermarket alignment aids, such as shims, that would allow the technician to make the necessary alignment corrections. While shims could correct a lot of alignment problems, don’t rely on them to cure every problem. Before wasting a lot of time and effort finding the right shim to use, if camber is less than specifications, be sure to check the ride height. If the springs are below minimum ride-height specifications, forget about using shims. To restore safe handling on such a vehicle, the springs should be replaced.
Types of Shim
There are several types of rear shims available that would assist in making camber and toe corrections on FWD (front wheel drive) cars and minivans. Make sure you are familiar with these types of shims.
Half Shims – These come in various sizes and thickness for use on General Motors, Chrysler, Volkswagen and Audi applications. Half shims could be used to make both camber and toe corrections. Most of these shims are metal and could be slid into place without having to unbolt and remove the rear spindle or wheel bearing.
The downside is that the half shim creates a small crevice into which dirt and water could penetrate. In addition, they do not provide as much support as a full-contact shim. The most common mistake made when using a half shim is installing it in the wrong position. Be sure to place it between the brake backing plate and axle. Placing it between the brake backing plate and hub could result in braking problems.
Full-Contact Shims – These come in various configurations and sizes. In addition, they come in both metal and plastic and different bolt patterns are needed for different applications. Full-contact shims could be used to provide .25 up to 1.5 degrees of camber or toe correction depending on the thickness of the shim.
Using a full-contact shim usually requires completely removing the spindle or wheel bearing and brake backing plate so the shim could be installed between the backing plate and axle or trailing arm. If the vehicle being serviced is equipped with anti-lock brakes, pay special attention to the wheel-speed sensor wiring. If not careful, this wiring could be easily damaged.
Two-Piece Adjustable Shims – A relatively few number of shims could fit a wide range of applications. Most two-piece adjustable shims are plastic. Installation is the same as with full-contact shims, except that adjustable shims must first be set or trimmed to achieve the desired amount of camber or toe correction.
When installing adjustable two-piece shims, make sure the shim faces the proper direction. On one side of the vehicle, the shim may face in, while on the other side it may face out. Positioning it the wrong way would give you just the opposite effect you are after.
Today’s high-tech alignment equipment could take a lot of the guesswork out of shim installation. The technician could call up the make and model of vehicle he is working on and with the click of his pointer, he could change the orientation angle of the shim and see the resulting change in camber and toe. The alignment machine makes all the calculations for the technician and presents the results in colourful animation.
Not only could the technician use this information to choose the correct shim and obtain installation instructions, he could also use the information provided by this equipment to help explain the needed service to the vehicle owner and to educate him on exactly what needs to be done to correct the problem. By printing out the diagrams from the monitor, the technician could show the vehicle owner exactly what is found out in the service bay.
If you have the right equipment and the knowledge to use it, don’t be afraid to charge for your time. The ability to return these hard-to-align vehicles to proper operating condition is something for which you should be fairly paid. Armed with the colour printouts mentioned earlier, the technician or service writer could explain to the customer why additional charges were necessary.
With the right equipment and training, technicians are able to align these vehicles that were once viewed as being unalignable. The key is keeping up with the new technology that is available in the aftermarket. It seems that as fast as automakers could release a new alignment system, somebody comes up with the needed fix.
To ensure the Malaysian tyre servicing providers are equipped with relevant knowledge and skills, Newera Equipment Supply Sdn Bhd, the Hunter sole distributor in Malaysia, has brought in not only the advanced alignment technology from Hunter but also the EZ Shim. With the EZ Shim kit, rear toe and camber are now adjustable, allowing the tyre servicing providers to provide precision alignment for maximum performance and prevent uneven tyre wear.
全接触垫片（Full Contact Shims）：一般拥有各种规格和尺寸。它们有金属和塑料两种材质，不同的螺栓款型供不同的应用。全接触垫片能用来校正0.25 至1.5度的外倾或前束，视该垫片的厚度而有所不同。