Collision Repair Training | Australia
|
Collision Repair Training | Australia
|
Current Events/News: Advantage Online: 2004 Archives
This article may be distributed and reproduced, but only by following the requirements stated in Permission to Reproduce. WHEEL ALIGNMENT QUICK CHECKS
March 29, 2004 - Diagnosing damaged suspension parts can be a difficult task when preparing a damage report. Many times, a bent part cannot be identified until the vehicle is measured with a three-dimensional measuring system, or until the vehicle is placed on the wheel alignment equipment. Although not as accurate as measuring equipment, there are a few simple measurements that can point the damage appraiser in the right direction when writing a damage report. This can help reduce delays in the repair process while waiting for parts to arrive, and can help ensure that a wheel alignment can be performed to meet the vehicle maker’s recommendations. Terms Knowledge of a few basic terms is required when performing these measurements, as well as a wheel alignment specifications reference manual (see Figure 1). Common terms that are used when performing an alignment are camber, caster, and toe (see Figures 2–4). Visual Inspection The first step when diagnosing a damaged suspension part is to perform a visual inspection. This should be done on a level surface with the front wheels placed on turntables. The visual inspection can be done by turning the steering wheel to the straight-ahead position and sighting down the length of the vehicle from the front to the rear, making a note of the position of the wheels. Next, sight down each wheel from the top and note the direction of the top of the wheel in relationship to the vehicle centerline. Also check the tire size, air pressure, and wheel size. All of these factors can cause inaccurate measurements if there is a variance. Tracking And Wheel Base Tracking is the direction that the rear wheels face in relationship to the front wheels. A quick measurement with a string and a tape measure can determine either a misaligned rear axle assembly, or an out-of-position engine cradle. Again, these quick checks should only be used to determine if further diagnostics or measurements are warranted. The tracking measurement is taken by running a piece of string in the middle of the tire down the length of the vehicle (see Figure 5). With the steering wheel unlocked and the front wheels placed on turntables, turn the wheel until the front and rear edge of the front tire touches the string. If the string does not touch the front edge of the rear tire, measure the distance between the string and the front edge of the rear tire sidewall at the narrowest point. If the string does touch the front edge of the rear tire, a measurement should be taken at the rear edge of the front tire (see Figure 6). Remove the string from the front tire and slowly move the string toward the front tire while measuring the distance between the string and the rear edge of the front tire. Record the measurement when the string touches the front edge of the rear tire. Next, measure the wheelbase (see Figure 7) by measuring the distance from the back edge of the rear rim to the back edge of the front rim when the front wheels are in the straight-ahead position. Record this measurement. Next, perform these measurements on the opposite side of the vehicle and record the measurements. Comparing these measurements from side-to-side and noting any differences can help indicate structural damage and damaged suspension parts. Camber A portable camber gauge can be used to indicate an approximate camber reading of each wheel. This is accomplished by placing either the front wheels or rear wheels on turntables and attaching the portable camber gauge on the wheel (see Figure 8). This camber reading can be compared to the vehicle maker’s specification. Any variations in the measurement from the vehicle maker’s specification may indicate damage to a steering knuckle or strut. What Do These Measurements Indicate? Differences in wheelbase measurements from side-to-side could indicate a bent wheel, a bent lower control arm, a shifted engine cradle, an out-of-position rear axle assembly, or structural damage. Further measurements will be required to determine if the vehicle structure is dimensionally correct. Other measurements between a lower ball joint and a symmetrical point on the vehicle underbody can also be used (see Figure 9). A difference in this measurement from side-to-side can identify a bent lower control arm. A short wheelbase measurement, when compared to vehicle maker’s specifications, will adversely affect the caster reading when a wheel alignment is performed on the vehicle. Differences in tracking measurements with a correct wheelbase measurement indicate either an out-of-position engine cradle or an out-of-position rear axle. Another possibility could be an out-of-specification rear toe measurement. Out-of-specification camber readings can indicate a bent McPherson strut, a bent steering knuckle, a shifted engine cradle, or misalignment of the unibody structure. Conclusion All of these measurements can be used to help diagnose suspension misalignment when writing a damage report. When these measurements are used in conjunction with three-dimensional measuring during structural repairs, it can inform the technician whether the vehicle can have the wheels aligned to the vehicle maker’s specifications. More information on steering and suspension system diagnostics and performing wheel alignments can be found in the I-CAR Wheel Alignment And Diagnostic Angles (STE04) program. Watch for it in your area.
|
||||||||||||||||||||||||
|
||||||||||||||||||||||||
|
Page Last Revised: |
||||||||||||||||||||||||
