Join Date: Nov 2000
Location: Manitoba, Canada
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Re: Caster Camber toe-in? Front ends for dummies
( A copyright enfringing cut and paste from Chilton's)
Front End Alignment
Proper alignment of the front wheels must be maintained in order to ensure ease of steering and satisfactory tire life.
The most important factors of front wheel alignment are wheel camber, axle caster, and wheel toe-in.
Wheel toe-in is the distance by which the wheels are closer together at the front than at the rear.
Wheel camber is the amount the top of the wheels incline outward from the vertical.
Front axle caster is the amount in degrees that the steering pivot pins are tilted toward the rear of the vehicle. Positive caster is inclination of the top of the pivot pin toward the rear of the vehicle.
These points should be checked at regular intervals, particularly when the front axle has been subjected to a heavy impact. When checking wheel alignment, it is important that wheel bearings be in proper adjustment. Loose bearings will affect instrument readings when checking the camber, pivot pin inclination, and toe-in.
Front wheel camber is preset. Some alignment shops can correct camber to some extent by installing special tapered shims between the steering knuckle and the spindle.
Caster is also preset, but can be altered by use of tapered shims between the axle pad and the springs. Wheel toe-in is adjustable.
To avoid damage to the U-joints, it is advisable to check the turning angle periodically. An adjustment turntable is advisable for properly determining the angle.
Correct turning angles are:
All 1971: 27.5° max.
1972-75 With standard (F78 x 15) tires: 34-35°. With larger optional tires: 31°
To adjust the turning angle, loosen the locknut (on some early models, a securing weld will have to be broken) and turn the adjusting screw. The adjusting screw is located on the axle tube near the knuckle on early models, and on the knuckle, just below the axle centerline on later models.
See Figure 1
Caster angle is established in the axle design by tilting the top of the kingpins forward so that an imaginary line through the center of the kingpins would strike the ground at a point ahead of the point of the contact.
The purpose of caster is to provide steering stability which will keep the front wheels in the straight ahead position and also assist in straightening up the wheels when coming out of a turn.
If the angle of caster, when accurately measured, is found to be incorrect, correct it to the specification given in this section by either installing new parts or installing caster shims between the axle pad and the springs.
If the camber and toe-in are correct and it is known that the axle is not twisted, a satisfactory check may be made by testing the vehicle on the road. Before road testing, make sure all tires are properly inflated, being particularly careful that both front tires are inflated to exactly the same pressure.
If the vehicle turns easily to either side but is hard to straighten out, insufficient caster for easy handling of the vehicle is indicated. If correction is necessary, it can usually be accomplished by installing shims between the springs and axle pads to secure the desired result.
Fig. 1: Diagram showing caster
See Figure 2
The purpose of camber is to more nearly place the weight of the vehicle over the tire contact patch on the road to facilitate ease of steering. The result of excessive camber is irregular wear of the tires on the outside shoulders and is usually caused by bent axle parts.
The result of excessive negative or reverse camber will be hard steering and possibly a wandering condition. Tires will also wear on the inside shoulders. Negative camber is usually caused by excessive wear or looseness of the front wheel bearings, axle parts or the result of a sagging axle.
Unequal camber may cause any or a combination of the following conditions: unstable steering, wandering, kickback or road shock, shimmy or excessive tire wear. The cause of unequal camber is usually a bent steering knuckle or axle end.
Correct wheel camber is set in the axle at the time of manufacture. It is important that the camber be the same on both front wheels.
Fig. 2: Diagram showing camber
See Figure 3
Toe-in may be adjusted with a line or straightedge as the vehicle tread is the same in the front and rear. To set the adjustment both tie rods must be adjusted as outlined below: Set the tie rod end of the steering bellcrank at right angles with the front axle. Place a straight edge or line against the left rear wheel and left front wheel to determine if the wheel is in a straight ahead position. If the front wheel tire does not touch the straight edge at both the front and rear, it will be necessary to adjust the left tie rod by loosening the clamps on each end and turning the rod until the tire touches the straight edge.
Check the right hand side in the same manner, adjusting the tie rod if necessary making sure that the bellcrank remains at right angles to the axle. When it is determined that the front wheels are in the straight ahead position, set the toe-in by shortening each tie rod approximately 1/2 turn.
First raise the front of the vehicle to free the front wheels. Turn the wheels to the straight ahead position. Use a Steady restŪ to scribe a pencil line in the center of each tire tread as the wheel is turned by hand. A good way to do this is to first coat a strip with chalk around the circumference of the tread at the center to form a base for a fine pencil line.
Measure the distance between the scribed lines at the front and rear of the wheels using care that both measurements are made at an equal distance from the floor. The distance between the lines should be greater at the rear than at the front by 3/64 in. (1.2mm) to 3/32 in. (2.2mm). To adjust, loosen the clamp bolts and turn the tie rod with a small pipe wrench. The tie rod is threaded with right and left hand threads to provide equal adjustment at both wheels. Do not overlook retightening the clamp bolts. It is common practice to measure between the wheel rims. This is satisfactory providing the wheels run true. By scribing a line on the tire tread, measurement is taken between the road contact points reducing error caused by wheel run-out.
Fig. 3: Diagram showing toe
END OF SECTION