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Manual Drivetrains and Axles Fourth Edition

Manual Drivetrains and Axles Fourth Edition. Tom Birch and Chuck Rockwood. Chapter 11 Drive Axles. A drive axle combines the drive gears with a differential and two axles to drive two wheels of a vehicle.

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Manual Drivetrains and Axles Fourth Edition

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  1. Manual Drivetrains and AxlesFourth Edition Tom BirchandChuck Rockwood Chapter 11 Drive Axles

  2. A drive axle combines the drive gears with a differential and two axles to drive two wheels of a vehicle.

  3. Hypoid ring and pinion gears are the final drive gearset. They are similar to a spiral bevel gearset.

  4. Knowledge of gear tooth terminology becomes important during gear adjustment.

  5. Backlash is the clearance between the ring and pinion gears.

  6. Most drive axles use an odd ratio, like 3.73:1. It is called a hunting gearset because each pinion gear tooth contacts every one of the ring gear teeth during 373 revolutions. Note the 750 on both gears that indicate a matched gearset. The +4 identifies the pinion depth.

  7. If the gear ratio is an even number like 4:1, each pinion gear tooth will touch the same four teeth of the ring gear. This is called a nonhunting gear set, and the gears must be timed.

  8. Animation: Hypoid Gearset PCMAC

  9. Most pinion gears are overhung and mounted on a pair of tapered roller bearings.

  10. The Ford 9” axle uses a straddle mounted pinion gear with a pair of tapered roller bearings plus a pilot bearing.

  11. The ring gear is attached to the differential which is mounted on a pair of tapered roller bearing. These are commonly called the carrier bearings.

  12. Axle service requires adjusting the bearing preload of the pinion and ring gears to prevent any sideways motion.

  13. A collapsible spacer, called a crush sleeve, is mounted between the bearings of most pinion gears.

  14. Carrier bearings are adjusted using either shims or threaded adjusters

  15. Vehicles equipped with ABS, antilock braking systems, have a VSS, vehicle speed sensor, mounted on the differential or A VSS mounted at the axle wheel ends.

  16. The differential ring gear and case drive the pinion shaft. The two pinion gears drive the two side gears but let them rotate at different speeds.

  17. Animation: Differential Operation PCMAC

  18. When a vehicle turns corners, the right and left tires must travel at different speeds.

  19. Animation: 2WD Differentials PCMAC

  20. A common, open differential splits torque equally between the two drive axles. • If one axle gets 50 ft. lbs. of torque, the other axle will get 50 ft. lbs. of torque. • But, if one wheel spins with 5 ft. lbs. of torque, the other axle will get only 5 ft. lbs. of torque. • The vehicle might become stuck.

  21. Limited slip (LS) differentials allow a speed differential so vehicles can turn corners, and they can bias the torque output to send more torque to one of the axles. There is a variety of LS differentials.

  22. One type of LS differential uses preloaded, mutliplate clutches that can drive the axles through either the differential gears or the clutch packs.

  23. The clutch packs must slip as the vehicle turns corners.

  24. Another type of LS differential uses two cone clutches in place to the multiplate clutches.

  25. This LS differential uses a governor weight that applies the clutches if there is too much wheel slip.

  26. Another type of LS differential uses two differential mate shafts and special case ramps to apply one of the clutch packs.

  27. Some differentials include a viscous coupling to deliver torque to the axle with good traction.

  28. The Vari-lock differential includes a oil punp that can apply the clutch pack if there is too much difference in wheel speed.

  29. A Torsen differential uses pairs of specially designed gears mated with worm-like axle gears to achieve a 5.0:1 torque bias.

  30. Several Honda vehicles drive the rear axles using electronically controlled multiplate clutches. A differential is not included.

  31. The inner end of an axle shaft floats as it is supported by the side gear.

  32. Most passenger car and light trucks use a single bearing at the outer end of the axle; this is called a semi-floating axle.

  33. Some semi-floating axles are held in the housing by the axle bearing retainer.

  34. Many semi-floating axles are held in the housing by a C-clip at the inner end. The axle slides through the axle bearing, becoming the inner bearing race.

  35. Trucks and heavy-duty pickups have a wheel hub with two wheel bearings outside of the housing, and the axle is bolted to it. This is called a full-floating axle.

  36. Ring gear rotation picks up and moves gear oil through the center section to lubricate the moving parts.

  37. Vehicles with independent suspension have a short carrier housing with two halfshafts to drive the wheels.

  38. Drive axles can be identified by a tag, stamped model number, and the shape of the cover.

  39. You can determine the axle ratio from the tag or by counting driveshaft revolutions as the wheel turns 20 revolutions.

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