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Chapter 21

Chapter 21. Rear-Wheel Drive Shafts, Universal Joints, and Axles. Introduction. While front-wheel drive has become the norm for automobiles, SUVs and trucks have become popular. For this reason, a thorough understanding of conventional rear-wheel drive systems is necessary. Driveline.

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Chapter 21

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  1. Chapter 21 Rear-Wheel Drive Shafts, Universal Joints, and Axles

  2. Introduction • While front-wheel drive has become the norm for automobiles, SUVs and trucks have become popular. • For this reason, a thorough understanding of conventional rear-wheel drive systems is necessary.

  3. Driveline • The driveline includes the drive shaft, universal joints (U-joints), axles, and axle bearings.

  4. Drive Shaft • Transfers power from the transmission to the differential. • The drive shaft must be balanced and straight.

  5. Slip Yoke • The slip joint allows the drive shaft to change lengths as the vehicle’s rear suspension moves up and down.

  6. Universal Joints • The drive shaft has U-joints that allow the drive shaft to operate at different angles as the rear suspension moves and the transmission stays stationary.

  7. Two-Piece Drive Shaft • Long drive shafts can flex and upset balance. • Instead of placing a single long drive shaft, the manufacturer may install a two-piece drive shaft. • A center support bearing is used where the two drive shafts meet.

  8. Drive Shaft Angle • When a universal joint is used at an angle, the shaft actually speeds up and slows down as it rotates. • As the joint angle increases, the change in velocity also increases. • Most U-joints can only tolerate an angle of 3 to 4 degrees.

  9. Constant Velocity Joints • If two U-joints are placed next to each other, a constant velocity joint can be made. • This is not a true constant velocity joint, but the speed change does not leave the yoke.

  10. Drive Shaft Service and Diagnosis • The drive shaft can make a clunking, squeaking, knocking, or grinding sound. • Make sure the drive shaft is the source of the problem before disassembling.

  11. Drive Shaft Service • Inspect the drive shaft for undercoating, missing weights, or damage. • Look for rust around the caps. • Inspect the motor and transmission mounts.

  12. Drive Shaft Service(continued) • Move the drive shaft back and forth and look for play between the U-joint and flange at the rear and yoke at the front.

  13. Universal Joint Diagnosis • The most common U-joint failure is squeaking due to a lack of grease. • A sharp click when putting in gear can also signal a failing U-joint.

  14. Drive Shaft Removal • Mark the drive shaft before removal. • Unbolt the U-joint at the differential. • Pry the shaft forward. • Secure the U-joint caps to prevent them from falling apart.

  15. Drive Axles and Bearings • There are two common types of drive axle bearings called semi-floating. • One type, called a bearing retained axle, has the axle bearing pressed on the axle shaft.

  16. C-Lock Axle • The C-lock axle bearing rests in the axle tube, and the inner race is actually the axle shaft.

  17. Independent Rear Suspension • Independent rear suspensions use either CV joints or U-joints for a flexible coupling between the differential and the wheels.

  18. Limited Slip Gear Oils • Limited slip differentials require additive to prevent lock-up during normal turning.

  19. Bearing Noise • Bearing noise can be diagnosed by carefully listening while driving the vehicle through turns. • The inside wheel always turns slower, and the noise should change as speed and load change during turns.

  20. Differential Noise • Bad carrier and pinion bearings will not change in corners because they are always driven at drive shaft speed.

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