Chapter 24

Heavy-Duty Truck

Axle Service and Repair

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.

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.

Axle Fill and Drain Plugs

Axle Lube Viscosity

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

Shop Talk

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

Power Divider Oil Fill and Drain Plugs

Checking the Lube Level

Proper Lubricant Levels

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.

Wheel Hub Lube Cavity

Differential Carrier Identification

Axle Identification

Crown Gear and Pinion Identification

Failure Analysis

• Shock load

• Fatigue

• Spinout

• Faulty lubrication

• Normal wear

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.

Fracture Patterns

Surface Failure Patterns

Torsional Failure

Bending Failure Patterns

Spinout

Always Support the Truck With Axle Stands

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.

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.

Thrust Screw

Marking the Carrier Components

Lock Plate and Adjusting Rings

Removing the Bearing Cap and Adjusting Ring

Differential Spider Gears

Drill and Punch Out Rivets

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.

Remove the Ring Gear

Removing the Pinion Flange or Yoke

Bearing Cage Removal

Removing Pinion with Bearing Cage

Pressing the Drive Pinion from the Bearing Cage

Pinion Bearing Removal

Spigot Bearing

Removing Power Divider

Power Divider Dowel Pins

Power Divider Assembly

Interaxle Differential

Measuring End Play

Pinion Bearing Cage Assembly

Check Pinion Bearing Preload

A Tool to Check Rolling Resistance

Checking Rolling Resistance

Drive Pinion Depth Controlled by Shim Pack Thickness

Pinion Cone Variation Number

Determining Shim Pack Thickness

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

Checking Crown Gear Runout

Check Crown Gear Backlash

Adjustments to Increase Backlash

Adjustments to Decrease Backlash

Crown Gear Tooth Nomenclature

Checking Tooth Contact

Correct Contact Pattern for Used Gearing

Incorrect Pinion Position

Incorrect Backlash Patterns

Adjusting the Thrust Screw

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.

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.

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

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.

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.

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.