# 2-Wheel Drive Coil Spring Front Suspension

## Introduction

A common 2-wheel drive Twin I-Beam front suspension, with ball joints

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F-150, F-250, and Expedition 2-wheel drive front suspension

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1999-00 F-250SD and F-350 2-wheel drive front suspension

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Trucks with 2-Wheel Drive and coil springs use two I-beam type front axles; one for each wheel. One end of each axle is attached to the spindle and a radius arm, and the other end is attached to a frame pivot bracket on the opposite side of the truck.

## Coil Springs

### REMOVAL & INSTALLATION

### 1997-98 F-250HD and F-350

Exploded view of front spring and shock absorber assembly—1997-98 2-wheel drive F-250HD and F-350 with ball joints

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1. Raise the front of the vehicle and place jackstands under the frame and a jack under the axle.
2. Remove the wheels.
3. Disconnect the shock absorber from the lower bracket.
4. Remove one bolt and nut and remove the rebound bracket.
5. Remove the two spring upper retainer attaching bolts from the top of the spring upper seat and remove the retainer.
6. Remove the nut attaching the spring lower retainer to the lower seat and axle and remove the retainer.
7. Place a safety chain through the spring to prevent it from suddenly coming loose. Slowly lower the axle and remove the spring.

To install:

8. Place the spring in position and raise the front axle.
9. Position the spring lower retainer over the stud and lower seat, and install the two attaching bolts.
10. Position the upper retainer over the spring coil and against the spring upper seat, and install the two attaching bolts.
11. Tighten the upper retaining bolts to 13-18 ft. lbs.; the lower retainer attaching nuts to 70-100 ft. lbs. (95-136 Nm).
12. Connect the shock absorber to the lower bracket. Torque the bolt and nut to 40-60 ft. lbs. (54-81 Nm). Install the rebound bracket.
13. Remove the jack and safety stands.

#### F-150, F-250 and Expedition

1. Raise and safely support the vehicle.
2. Remove the wheel and tire assembly.
3. Remove the disc brake caliper and support aside with wire to prevent damage to the brake hose.
4. Remove 2 retaining bolts and the disc brake adapter.
5. Remove the brake rotor.
6. Remove 3 retaining bolts and the brake rotor splash shield.
7. Remove the shock absorber.
8. Remove the bracket supporting the brake hose.
9. Remove the stabilizer bar link retaining nut and bushing from the lower control arm. Separate the stabilizer bar link from the lower control arm.
10. Install Coil Spring Compressor D78P-5310A or equivalent and compress the coil spring enough to relieve the tension of the spring between the upper and lower control arms.
11. Remove the cotter pin and castellated nut from the lower ball joint. Using Pitman Arm Puller T64P-3590-F or equivalent, separate the lower ball joint from the wheel spindle.
12. Match mark the lower control arm alignment cams for installation reference.
13. Remove the lower control arm retaining nuts and bolts.
14. Remove the lower control arm and the compressed coil spring as an assembly.
15. Loosen the coil spring compressor and remove the coil spring from the lower control arm.
16. Inspect the coil spring and replace as needed.

To install:

17. Place the coil spring correctly in the saddle of the lower control arm. Install the coil spring compressor and compress the coil spring. The end of the coil spring A, must cover the hole designated B and be visible in the second hole designated as C, for proper installation.
18. Place the lower control arm to the frame. Install the retaining bolts, adjusting cams, and nuts.
19. Align the match marks on the adjusting cams. The forward nut must be tighten first while the control arm is held at the curb position height. Tighten the nuts to 197-241 ft. lbs. (270-330 Nm).
20. Install the lower ball joint stud into the wheel spindle. Install the castellated nut and tighten to 83-113 ft. lbs. (113-153 Nm). Install a new cotter pin.
21. Connect the stabilizer bar link to the lower control arm. Install the bushing and retaining nut. Tighten to 15-21 ft. lbs. (21-29 Nm).
22. Remove the coil spring compressor.
23. Install the shock absorber. Tighten the lower bolts to 22 ft. lbs. (32 Nm) and the top nut to 45 ft. lbs. (61 Nm).
24. Connect the brake hose bracket.
25. Install the brake rotor splash shield. Install 3 retaining bolts and tighten to 90-107 inch lbs. (10-14 Nm).
26. Install the disc brake rotor and caliper assemblies.
27. Install the wheel and tire assembly.
28. Lower the vehicle.
29. Pump the brake pedal several times to position the brake pads prior to moving the vehicle.
30. Check the alignment and adjust if out of specification.
31. Road test the vehicle and check for proper operation.

#### 1999-00 F-250SD and F-350

1. Remove the front shock absorber. Refer to the procedure in this section.
2. Remove the wheel and tire assembly.
3. Using a suitable jack, support the front axle assembly.
4. Remove the upper spring retainer.
5. Lower the front axle until the spring is free of the upper spring seat.
6. Using an extension through the top of the spring, remove the lower spring retainer.
7. Remove the front spring.
8. The installation is the reverse of the removal.

## Shock Absorbers

### TESTING

The purpose of the shock absorber is simply to limit the motion of the spring during compression and rebound cycles. If the vehicle is not equipped with these motion dampers, the up and down motion would multiply until the vehicle was alternately trying to leap off the ground and to pound itself into the pavement.

Contrary to popular rumor, the shocks do not affect the ride height of the vehicle. This is controlled by other suspension components such as springs and tires. Worn shock absorbers can affect handling; if the front of the vehicle is rising or falling excessively, the "footprint" of the tires changes on the pavement and steering is affected.

The simplest test of the shock absorber is simply push down on one corner of the unladen vehicle and release it. Observe the motion of the body as it is released. In most cases, it will come up beyond it original rest position, dip back below it and settle quickly to rest. This shows that the damper is controlling the spring action. Any tendency to excessive pitch (up-and-down) motion or failure to return to rest within 2-3 cycles is a sign of poor function within the shock absorber. Oil-filled shocks may have a light film of oil around the seal, resulting from normal breathing and air exchange. This should NOT be taken as a sign of failure, but any sign of thick or running oil definitely indicates failure. Gas filled shocks may also show some film at the shaft; if the gas has leaked out, the shock will have almost no resistance to motion.

When fluid is seeping out of the shock absorber, it's time to replace it

While each shock absorber can be replaced individually, it is recommended that they be changed as a pair (both front or both rear) to maintain equal response on both sides of the vehicle. Chances are quite good that if one has failed, its mate is weak also.

### REMOVAL AND INSTALLATION

#### 1997-98 F-250HD and F-350

1. Raise the vehicle and secure on support stands.
2. Remove the self-locking nut, steel washer, and rubber bushings at the upper end of the shock absorber.
3. Remove the bolt and nut at the lower end and remove the shock absorber.

To install:

4. When installing a new shock absorber, use new rubber bushings. Position the shock absorber on the mounting brackets with the stud end at the top. Install the upper bushing, steel washer and self-locking nut at the upper end, and the bolt and nut at the lower end.
5. Torque the upper mounting studs to 18-22 ft. lbs. and the lower mounting nuts to 40-60 ft. lbs.

#### F-150, F-250 and Expedition

1. Hold the shock absorber stem and remove the nut from the top of the shock.
2. Raise and safely support the vehicle.
3. Remove 2 lower retaining nuts and remove the shock absorber.

To install:

4. Install 1 washer and bushing to the top stem of the shock absorber.
5. Place the shock absorber up through the coil spring.
6. Install 2 lower retaining nuts. Tighten the nuts to 19-25 ft. lbs. (26-34 Nm).
7. Lower the vehicle.
8. Install the bushing, washer and retaining nut to the top of the shock absorber stud. Tighten the nut to 34-46 ft. lbs. (47-63 Nm).
9. Road test the vehicle and check for proper operation.

#### 1999-00 F-250SD and F-350

1. Raise the hood and remove the upper shock absorber retaining nut and upper shock absorber insulator.
2. Raise and support the vehicle.
3. Remove the lower shock absorber retaining nut and remove the shock absorber.
4. The installation is the reverse of the removal.

## Upper Ball Joints

### INSPECTION

1. Before an inspection of the ball joint, make sure the front wheel bearings are properly packed and adjusted.
2. Jack up the front of the truck and safely support it with jackstands, placing the stands under the I-beam axle, beneath the spring.
3. Have a helper grab the lower edge of the tire and move the wheel assembly in and out.
4. While the wheel is being moved, observe the lower spindle arm and the lower part of the axle jaw (the end of the axle to which the spindle assembly attaches). If there is 1/32 in. (0.8mm) or greater movement between the lower part of the axle jaw and the lower spindle arm, the lower ball joint must be replaced.
5. To check upper ball joints, grab the upper edge of the tire and move the wheel in and out. If there is 1/32 in. (0.8mm) or greater movement between the upper spindle arm and the upper part of the jaw, the upper ball joint must be replaced.

### REMOVAL AND INSTALLATION

#### F-250HD/SD and F-350

Remove the ball joint with the special tool

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Use the C-frame as shown to install the ball joint

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WARNING
Do not use a forked ball joint removal tool to separate the ball joints as this will damage the seal and the ball joint socket. Do not use heat to aid in removal or installation of any suspension parts or components.

1. Raise and safely support the vehicle.
2. Remove the wheel and tire assembly.
3. Remove the front brake caliper assembly and support it from the body way with wire. Do not disconnect the brake line or allow the caliper to hang on the brake line.
4. Remove the brake rotor/hub assembly.
5. Remove the wheel spindle or steering knuckle assembly with the ball joints attached.
6. Place the spindle/knuckle assembly in a suitable vise.
7. Remove the lower ball joint. This is required to access the upper ball joint.
8. Remove the snap-ring from the upper ball joint.
9. Install U-Joint Remover T74P-4635-C and Receiver Cup D81T-3010-A or equivalents, on the upper ball joint. Turn the forcing screw clockwise until the upper ball joint is pressed out of the spindle/knuckle assembly.

To install:

10. Place the new upper ball joint to the spindle/knuckle assembly and install U-Joint Remover T74P-4635-C, Receiver Cup D81T-3010-A5 and Installation Cup D81T-3010-A1, or equivalents. Turn the forcing screw clockwise until the upper ball joint is seated.
11. Install the snap-ring onto the upper ball joint.
12. Install the lower ball joint.
13. Remove the spindle/knuckle assembly from the vise and install to the axle arm.
14. Install the brake rotor/hub assembly.
15. Install the front brake caliper assembly.
16. Install the wheel and tire assembly. Torque the lug nuts to 100 ft. lbs. (135 Nm).
17. Lower the vehicle.
18. Pump the brake pedal several times to position the brake pads before moving the vehicle.
19. Check the alignment and adjust if not within specification.
20. Road test the vehicle and check for proper operation.

#### F-150, F-250 and Expedition

The upper ball joint is an integral part of the upper control arm and is not a serviceable component. Replacement of the ball joint requires replacing the upper control arm assembly.

## Radius Arm

### REMOVAL & INSTALLATION

#### F-250HD/SD and F-350

Exploded view of the radius arm assembly—2-wheel drive F-250HD and F-350 models

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A torque wrench with a capacity of at least 350 ft. lbs. (475 Nm) is necessary, along with other special tools, for this procedure.

1. Raise the front of the vehicle and place jackstands under the frame and a jack under the wheel or axle. Remove the wheels.
2. Disconnect the shock absorber from the radius arm bracket.
3. Remove the two spring upper retainer attaching bolts from the top of the spring upper seat and remove the retainer.
4. Remove the nut which attached the spring lower retainer to the lower seat and axle and remove the retainer.
5. Lower the axle and remove the spring.
6. Remove the spring lower seat and shim from the radius arm. The, remove the bolt and nut which attach the radius arm to the axle.
7. Remove the cotter pin, nut and washer from the radius arm rear attachment.
8. Remove the bushing from the radius arm and remove the radius arm from the vehicle.
9. Remove the inner bushing from the radius arm.

To install:

10. Position the radius arm to the axle and install the bolt and nut finger-tight.
11. Install the inner bushing on the radius arm and position the arm to the frame bracket.
12. Install the bushing, washer, and attaching nut. Tighten the nut to 120 ft. lbs. (162 Nm) and install the cotter pin.
13. Tighten the radius arm-to-axle bolt to 269-329 ft. lbs. (365-446 Nm).
14. Install the spring seat and insulator on the radius arm so that the hole in the seat fits over the arm-to-axle nut.
15. Install the spring.
16. Connect the shock absorber. Tighten the nut and bolt to 40-60 ft. lbs. (54-81 Nm).
17. Install the wheels.

## Stabilizer Bar

### REMOVAL & INSTALLATION

#### 1997-98 F-250HD and F-350

Front stabilizer bar installation—2-wheel drive F-250HD and F-350 models

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1. Raise and support the front end on jackstands.
2. Disconnect the right and left stabilizer bar ends from the link assembly.
3. Disconnect the retainer bolts and remove the stabilizer bar.
4. Disconnect the stabilizer link assemblies by loosening the right and left lock-nuts from their respective brackets on the I-beams.

To install:

5. Loosely install the entire assembly. The links are marked with an R and L for identification.
6. Tighten the link-to-stabilizer bar and axle bracket fasteners to 70 ft. lbs. (95 Nm).
7. Check to make sure that the insulators are properly seated and the stabilizer bar is centered.
8. Tighten the stabilizer bar-to-frame retainer bolts to 35 ft. lbs. (47 Nm). Tighten the frame mounting bracket nuts/bolts to 65 ft. lbs. (88 Nm).

#### F-150, F-250 And Expedition

1. Raise and safely support the vehicle.
2. Remove both stabilizer bar-to-stabilizer bar link retaining nuts, washers and bushings and separate the stabilizer bar ends from the stabilizer bar links.
3. Remove the stabilizer bar links from the lower control arms, if needed.
4. Remove 4 bolts securing 2 stabilizer bar insulator brackets.
5. Remove the stabilizer bar brackets and the stabilizer bar.

To install:

6. Place the stabilizer bar in position and install 2 stabilizer bar insulator brackets. Install 4 retaining bolts and tighten to 19-26 ft. lbs. (26-35 Nm).
7. Install the stabilizer bar links to the lower control arms, if removed.
8. Connect the stabilizer bar to the stabilizer bar links. Install the bushings, washers and retaining nuts. Tighten the stabilizer bar link retaining nuts to 12-15 ft. lbs. (15-20 Nm).
9. Lower the vehicle.
10. Road test the vehicle and check for proper operation.

#### 1999-00 F-250SD and F-350

1. Raise and support the vehicle.
2. Remove the stabilizer bar retainer brackets retaining bolts and remove the brackets.
3. Remove the lower stabilizer bar link nuts, washers and bolts.
4. Remove the stabilizer bar.
5. Remove the upper stabilizer bar link nuts and bolts, and remove the links.
6. The installation is the reverse of the removal.

## Twin I-Beam Axles

### REMOVAL & INSTALLATION

#### F-250HD/SD and F-350

Axle pivot bracket and axle arm installation—2-wheel drive F-250HD and F-350 models

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Installing axle pivot bushing

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A torque wrench with a capacity of at least 350 ft. lbs. (475 Nm) is necessary, along with other special tools, for this procedure.

1. Raise and support the front end on jackstands.
2. Remove the spindles.
3. Remove the springs.
4. Remove the stabilizer bar.
5. Remove the lower spring seats from the radius arms.
6. Remove the radius arm-to-axle bolts.
7. Remove the axle-to-frame pivot bolts and remove the axles.

To install:

8. Position the axle on the pivot bracket and loosely install the bolt/nut.
9. Position the other end on the radius arm and install the bolt. Tighten the bolt to 269-329 ft. lbs. (365-446 Nm).
10. Install the spring seats.
11. Install the springs.
12. Tighten the axle pivot bolts to 120-150 ft. lbs. (163-203 Nm).
13. Install the spindles.
14. Install the stabilizer bar.

## Front Wheel Knuckle and Spindle

### REMOVAL & INSTALLATION

#### F-250HD/SD and F-350

Exploded view of the front wheel spindle— 2-wheel drive F-250HD and F-350 with ball joints

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Spindle removal

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All 2-Wheel Drive pick-ups utilize upper and lower ball joints.

1. Jack up the front of the truck and safely support it with jackstands.
2. Remove the wheels.
3. Remove the front brake caliper assembly and hold it out of the way with a piece of wire. Do not disconnect the brake line.
4. Remove the brake rotor from the spindle.
5. Remove the inner bearing cone and seal. Discard the seal, as you'll be fitting a new one during installation.
6. Remove the brake dust shield.
7. Disconnect the steering linkage from the spindle arm using a tie rod removal tool.
8. Remove the cotter from the upper and lower ball joint stud nuts. Discard the cotter pins, as new ones should be installed during reassembly.
9. Remove the upper ball joint nut and loosen the lower ball joint nut to the end of the threads.
10. Strike the inside area or the spindle as shown in the illustration to pop the ball joints loose from the spindle.

WARNING
Do not use a forked ball joint removal tool to separate the ball joints as this will damage the seal and ball joint socket.

11. Remove the nut. Remove the spindle.

To install:

Before reassembly, be advised that new cotter pins should be used on the ball joints, and that new bearing seal(s) should also be used. Also, make sure the upper and lower ball joint seals are in place.

12. Place the spindle over the ball joints.
13. Install the nuts on the lower ball joint stud and partially tighten to 35 ft. lbs. (47 Nm). Turn the castellated nut until you are able to install the cotter pin.
14. Install the camber adapter in the upper spindle over the upper ball joint stud. Be sure the adapter is aligned properly.

If camber adjustment is necessary special adapters must be installed.

15. Install the nut on the upper ball joint stud. Hold the camber adapter with a wrench to keep the ball stud from turning. If the ball stud turns, tap the adapter deeper into the spindle. Tighten the nut to 110-140 ft. lbs. (149-190 Nm) and continue tightening the castellated nut until it lines up with the hole in the stud. Install the cotter pin.
16. Tighten the lower nut to 110-140 ft. lbs. (149-190 Nm). Advance the nut to install a new cotter pin.
17. Install the brake dust shield.
18. Pack the inner and outer bearing cone with a quality wheel bearing grease by hand, working the grease through the cage behind the roller.
19. Install the inner bearing cone and seal. Install the hub and rotor on the spindle.
20. Install the outer bearing cone, washer, and nut. Adjust the bearing end-play and install the nut retainer, cotter pin and dust cap.
21. Install the brake caliper. connect the steering linkage to the spindle. Tighten the nut to 70-100 ft. lbs. (95-135 Nm) and advance the nut as far necessary to install the cotter pin.
22. Install the wheels. Lower the truck and adjust toe-in if necessary.

#### F-150, F-250 and Expedition

WARNING
The electrical power to the air suspension system must be shut off prior to hoisting, jacking, or towing an air suspension vehicle. This can be accomplished by turning off the air suspension switch located in the PASSENGER SIDE kick panel area. Failure to do so can result in unexpected inflation or deflation of the air springs, which can result in shifting of the vehicle during these operations.

1. Raise and safely support the vehicle securely on jackstands.
2. Remove the wheel and tire assembly.
3. Remove the brake disc shield.
4. Use a suitable jack to support the front suspension lower arm.
5. Remove the upper ball joint castellated nut.
6. Remove the cotter pin.
7. Remove the ball joint nut.
8. Use the Pitman Arm Puller to separate the ball joint from the front wheel spindle.
9. Remove the upper shock absorber nut.
10. Remove two shock absorber lower nuts.
11. Remove the front shock absorber.
12. Remove the cotter pin.
13. Remove the castellated nut.
14. Use the Pitman Arm Puller to separate the tie rod end from the front wheel spindle.
15. Use the Coil Spring Compressor to compress the coil spring.
16. Remove the lower ball joint cotter pin.
17. Remove lower ball joint castellated nut.
18. Use the Pitman Arm Puller to separate the lower ball joint from the front wheel spindle.
19. Remove the front wheel spindle.

To install:

20. Install the lower ball joint castellated nut.
21. Install a new cotter pin.
22. Install the upper ball joint castellated nut.
23. Install a new cotter pin.
24. Remove the Coil Spring Compressor.
25. Install the tie rod castellated nut.
26. Install a new cotter pin.
27. Install the front shock absorber and the two shock absorber lower nuts.
28. Install the upper shock absorber nut.
29. Install the brake disc shield.
30. If equipped with air suspension, reactivate the system by turning on the air suspension switch.
31. Install the tire and wheel assembly.
32. Inspect and adjust the front end alignment.

## Lower Ball Joint

### INSPECTION

Refer to Inspection under Upper Ball Joint in this section.

### REMOVAL & INSTALLATION

#### F-250HD/SD and F-350

Remove the ball joint with the special tool

Click to enlarge

Use the C-frame as shown to install the ball joint

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Lower ball joint installation

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WARNING
Do not use a forked ball joint removal tool to separate the ball joints as this will damage the seal and the ball joint socket. Do not use heat to aid in removal or installation of any suspension parts or components.

1. Raise and safely support the vehicle.
2. Remove the wheel and tire assembly.
3. Remove the front brake caliper assembly and support it from the body way with wire. Do not disconnect the brake line or allow the caliper to hang on the brake line.
4. Remove the brake rotor/hub assembly.
5. Remove the wheel spindle or steering knuckle assembly with the ball joints attached.
6. Place the spindle/knuckle assembly in a suitable vise.
7. Remove the lower ball joint. This is required to access the upper ball joint.
8. Remove the snap-ring from the upper ball joint.
9. Install U-Joint Remover T74P-4635-C and Receiver Cup D81T-3010-A or equivalents, on the upper ball joint. Turn the forcing screw clockwise until the upper ball joint is pressed out of the spindle/knuckle assembly.

To install:

10. Place the new upper ball joint to the spindle/knuckle assembly and install U-Joint Remover T74P-4635-C, Receiver Cup D81T-3010-A5 and Installation Cup D81T-3010-A1, or equivalents. Turn the forcing screw clockwise until the upper ball joint is seated.
11. Install the snap-ring onto the upper ball joint.
12. Install the lower ball joint.
13. Remove the spindle/knuckle assembly from the vise and install to the axle arm.
14. Install the brake rotor/hub assembly.
15. Install the front brake caliper assembly.
16. Install the wheel and tire assembly.
17. Lower the vehicle.
18. Pump the brake pedal several times to position the brake pads before moving the vehicle.
19. Check the alignment and adjust if not within specification.
20. Road test the vehicle and check for proper operation.

#### F-150, F-250 and Expedition

The lower ball joint is an integral part of the lower control arm and is not a serviceable component. Replacement of the ball joint requires replacing the lower control arm.

## Hub and Bearing

### REMOVAL & INSTALLATION

#### F-150, F-250 and Expedition

The hub is part of the disc brake rotor and cannot be serviced separately. The inner and outer wheel bearing and races are serviced individually. Make sure to have a new hub grease seal when servicing the wheel bearings.

1. Raise and safely support the vehicle.
2. Remove the wheel and tire assembly.
3. Remove the disc brake caliper.
4. Remove the disc brake pads and anti-rattle clips.
5. Remove 2 anchor plate retaining bolts and remove the anchor plate.
6. Remove the hub grease cap, cotter pin, retainer washer and the spindle nut.
7. Remove the wheel bearing retainer washer and the outer wheel bearing.
8. Remove the disc brake hub and rotor assembly.
9. Using a suitable seal remover, remove and discard the hub grease seal.
10. Remove the inner wheel bearing.
11. Clean and inspect the wheel bearings and races for unusual wear or damage. Replace parts as necessary.
12. Inspect the hub and brake rotor assembly. If required, the hub and brake rotor assembly must be replaced as a unit.

To install:

13. If needed, pack the wheel bearing with a suitable high temperature wheel bearing grease before assembly.
14. Install the inner wheel bearing in the hub and brake rotor assembly.
15. Install a new grease seal using a suitable installation tool.
16. Place the hub and rotor assembly on the wheel spindle and install the outer wheel bearing.
17. Install the retainer washer and the spindle nut.
18. Adjust the wheel bearings as follows:
    1. Torque the spindle nut to 17-24 ft. lbs. (23-34 Nm) while rotating the wheel and tire assembly to seat the wheel bearings.
    2. Back off the spindle nut no less than 1/2 turn.
    3. Torque the spindle nut to 17 inch lbs. (2 Nm).
19. Install the retaining washer so the castellations are aligned with the cotter pin hole. Install a new cotter pin.
20. Place the anchor plate and install 2 retaining bolts. Tighten the bolts to 125-168 ft. lbs. (170-230 Nm).
21. Install the brake pad anti-rattle clips and install the disc brake pads.
22. Install the disc brake caliper.
23. Install the wheel and tire assembly. Torque the lug nuts to 83-112 ft. lbs. (113-153 Nm).
24. Check the wheel and tire assembly for proper rotation, then install the grease cap.
25. Lower the vehicle.
26. Road test the vehicle and check for proper operation.

## Front Wheel Bearings

Refer to Brake Rotor in Section 9 for removal and installation of the wheel bearings.

## Wheel Alignment

If the tires are worn unevenly, if the vehicle is not stable on the highway or if the handling seems uneven in spirited driving, the wheel alignment should be checked. If an alignment problem is suspected, first check for improper tire inflation and other possible causes. These can be worn suspension or steering components, accident damage or even unmatched tires. If any worn or damaged components are found, they must be replaced before the wheels can be properly aligned. Wheel alignment requires very expensive equipment and involves minute adjustments which must be accurate; it should only be performed by a trained technician. Take your vehicle to a properly equipped shop.

Following is a description of the alignment angles which are adjustable on most vehicles and how they affect vehicle handling. Although these angles can apply to both the front and rear wheels, usually only the front suspension is adjustable.

### CASTER

Looking at a vehicle from the side, caster angle describes the steering axis rather than a wheel angle. The steering knuckle is attached to a control arm or strut at the top and a control arm at the bottom. The wheel pivots around the line between these points to steer the vehicle. When the upper point is tilted back, this is described as positive caster. Having a positive caster tends to make the wheels self-centering, increasing directional stability. Excessive positive caster makes the wheels hard to steer, while an uneven caster will cause a pull to one side. Overloading the vehicle or sagging rear springs will affect caster, as will raising the rear of the vehicle. If the rear of the vehicle is lower than normal, the caster becomes more positive.

Caster affects straight-line stability. Caster wheels used on shopping carts, for example, employ positive caster

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### CAMBER

Looking from the front of the vehicle, camber is the inward or outward tilt of the top of wheels. When the tops of the wheels are tilted in, this is negative camber; if they are tilted out, it is positive. In a turn, a slight amount of negative camber helps maximize contact of the tire with the road. However, too much negative camber compromises straight-line stability, increases bump steer and torque steer.

Camber influences tire contact with the road

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### TOE

Looking down at the wheels from above the vehicle, toe angle is the distance between the front of the wheels, relative to the distance between the back of the wheels. If the wheels are closer at the front, they are said to be toed-in or to have negative toe. A small amount of negative toe enhances directional stability and provides a smoother ride on the highway.

With toe-in, the distance between the wheels is closer at the front than at the rear

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