Heavy-Duty Truck

1
Chapter 24

• Heavy-Duty Truck
• Axle Service and Repair

2
Objectives (1 of 2)

• Describe the lubrication requirements of truck
  and trailer dead axles.
• Outline the lubrication service procedures
  required for truck drive axle assemblies.
• Perform some basic level troubleshooting on
  differential carrier gearing.
• Outline the procedure required to disassemble a
  differential carrier.

3
Objectives (2 of 2)

• Disassemble a power divider unit.
• Perform failure analysis on power divider and
  differential carrier components.
• Reassemble power divider and differential carrier
  assemblies.

4
Axle Fill and Drain Plugs
5
Axle Lube Viscosity

• See Table 24-1 on page 706 in the textbook.

6
Shop Talk

• Draining lubricants when warm ensures that
  contaminants are still suspended and also reduces
  drain time.

7
Power Divider Oil Fill and Drain Plugs
8
Checking the Lube Level
9
Proper Lubricant Levels
10
Caution

• On most drive axles, there is no external visual
  means of checking lubricant level in the wheel
  end, so the importance of making sure the drive
  axle lubricant level is correct cannot be
  overemphasized.
• Raising each side of an axle with a jack ensures
  oil fills the wheel-end hub cavity.
• Make a final check of the differential carrier
  oil level after tilting the axle from both sides.

11
Wheel Hub Lube Cavity
12
Differential Carrier Identification
13
Axle Identification
14
Crown Gear and Pinion Identification
15
Failure Analysis

• Shock load
• Fatigue
• Spinout
• Faulty lubrication
• Normal wear

16
Caution

• Most driver-abuse generated failures do not cause
  an instantaneous equipment failure.
• The equipment failure can take place some time
  after the driving incident that generated it.
• This is important to remember when attempting to
  attribute blame in fleets that do not assign
  drivers dedicated trucks.

17
Fracture Patterns
18
Surface Failure Patterns
19
Torsional Failure
20
Bending Failure Patterns
21
Spinout
22
Always Support the Truck With Axle Stands
23
Shop Talk

• You sometimes have to use more force to pop axle
  shafts than can be delivered using a drift and
  4-lb. hammer.
• When this method does not work, use a 16-lb.
  sledgehammer directly on center of the axle shaft
  flange use a ¼ swing of the sledgehammer,
  letting the weight of the hammer do all of the
  work.

24
Caution

• Most of the weight of a differential carrier
  assembly is on the inboard side of its mounting
  flange.
• Ensure that the assembly is properly fastened to
  the jacking device and that your body is never
  positioned under the carrier.

25
Thrust Screw
26
Marking the Carrier Components
27
Lock Plate and Adjusting Rings
28
Removing the Bearing Cap and Adjusting Ring
29
Differential Spider Gears
30
Drill and Punch Out Rivets
31
Caution

• Do not remove the rivet heads or rivets with a
  chisel and hammer because this can damage the
  flange case half or enlarge the rivet holes,
  resulting in loose rivets.

32
Remove the Ring Gear
33
Removing the Pinion Flange or Yoke
34
Bearing Cage Removal
35
Removing Pinion with Bearing Cage
36
Pressing the Drive Pinion from the Bearing Cage
37
Pinion Bearing Removal
38
Spigot Bearing
39
Removing Power Divider
40
Power Divider Dowel Pins
41
Power Divider Assembly
42
Interaxle Differential
43
Measuring End Play
44
Pinion Bearing Cage Assembly
45
Check Pinion Bearing Preload
46
A Tool to Check Rolling Resistance
47
Checking Rolling Resistance
48
Drive Pinion Depth Controlled by Shim Pack
Thickness
49
Pinion Cone Variation Number
50
Determining Shim Pack Thickness

• See Figure 24-59 on page 732 of the textbook.

51
Checking Crown Gear Runout
52
Check Crown Gear Backlash
53
Adjustments to Increase Backlash
54
Adjustments to Decrease Backlash
55
Crown Gear Tooth Nomenclature
56
Checking Tooth Contact
57
Correct Contact Pattern for Used Gearing
58
Incorrect Pinion Position
59
Incorrect Backlash Patterns
60
Adjusting the Thrust Screw
61
Summary (1 of 6)

• Adhering to OEM-recommended lubrication schedules
  is the key to ensuring the longest service life
  from both drive and dead axles.
• Knowing the correct procedure to check lubricant
  level is essential.
• The level is correct when lubricant is exactly
  level with the bottom of the fill hole.

62
Summary (2 of 6)

• Because most OEMs approve of the use of synthetic
  lubricants in final drive carriers, lubrication
  drain schedules have been greatly increased in
  recent years.
• Drain schedules are determined by the actual
  lubricant used and the type of application to
  which the vehicle is subjected.
• Servicing of axles on heavy-duty trucks consists
  of routine inspection, lubrication, cleaning,
  and, when required, troubleshooting and component
  overhaul.

63
Summary (3 of 6)

• Failure analysis is required to prevent recurrent
  failures.
• Drive axle carrier components usually fail for
  one of the following reasons
• Shock load
• Fatigue
• Spinout
• Lubrication problems
• Normal wear

64
Summary (4 of 6)

• Most differential carriers are replaced as
  rebuilt/exchange units, so the role of the
  technician is, more often than not, to diagnose
  the problem and then, if necessary, replace the
  defective assembly as a unit.
• The technician who has disassembled and
  reassembled differential carriers should find
  troubleshooting procedures easier to follow.

65
Summary (5 of 6)

• Follow the OEM procedure when disassembling
  differential carriers.
• Taking a few moments to measure shim packs and
  gear tooth contact patterns on disassembly can
  save considerable time when reassembling the
  carrier.
• A crown and pinion gearset often can be reused
  when rebuilding a differential carrier. Make sure
  you inspect it properly on disassembly.

66
Summary (6 of 6)

• Crown and pinion gearsets are always replaced as
  a matched pair during a rebuild.
• When setting crown and pinion backlash, it is
  increased by moving the crown gear away from the
  drive pinion, and decreased by moving the crown
  gear toward the drive pinion.