AXSM0055 Service Manual

This symbol is used throughout this manual to call attention to procedures where carelessness or failure to follow specific instructions may result in personal injury and/or component damage.

Departure from the instructions, choice of tools, materials and recommended parts mentioned in this publication may jeopardize the personal safety of the service technician or vehicle operator.

WARNING: Failure to follow indicated procedures creates a high risk of personal injury to the servicing technician.

CAUTION: Failure to follow indicated procedures may cause component damage or malfunction.

IMPORTANT: Highly recommended procedures for proper service of this unit.

NOTE: Additional service information not covered in the service procedures.

TIP: Helpful removal and installation procedures to aid in the service of this unit.

DEM: Refer to the OEM vehicle specifications

Failure analysis is the process of determining the original cause of a component failure in order to keep it from happen- ing again. Too often, when a failed component is replaced without determining its cause, there will be a recurring failure.

If a carrier housing is opened, revealing a ring gear with a broken tooth, it is not enough to settle on the broken tooth as the cause of the carrier failure. Other parts of the carrier must be examined.

For a thorough understanding of the failure and possible insight into related problems, the technician needs to observe the overall condition of the vehicle.

No one benefits when a failed component goes on the junk pile with the cause unknown. Nothing is more disturbing to a customer than a repeat failure.

Systematically analyzing a failure to prevent a repeat occurrence assures quality service by avoiding unnecessary downtime and further expense to the customer.

The true cause of a failure can be better determined by knowing what to look for, determining how a piece of the equipment was running and learning about previous problems. In the case of a rebuilt rear axle, mismatched gears may have been installed.

The more successful shops prevent repeat equipment failures by developing good failure analysis practices. Knowing how to diagnose the cause of a premature failure is one of the prerequisites of a good heavy-equipment technician.

The following five steps are an effective approach to good failure diagnostics.

Document the problem.

Make a preliminary investigation.

Prepare the parts for inspection.

Find the cause of the failure.

Correct the cause of the problem.

Here are some guidelines for starting to learn about a failure, including questions to ask:

Talk to the operator of the truck.

Look at the service records.

Find out when the truck was last serviced.

Ask: In what type of service is the truck being used?

Ask: Has this particular failure occurred before?

Ask: How was the truck working prior to the failure?

You need to be a good listener. Sometimes, insignificant or unrelated symptoms can point to the cause of the failure:

Ask: Was the vehicle operating at normal temperatures?

Ask: Were the gauges showing normal ranges of operation?

Ask: Was there any unusual noise or vibration?

After listening, review the previous repair and maintenance records. If there is more than one driver, talk to all of them and compare their observations for consistency with the service and maintenance records.

Verify the chassis Vehicle Identification Number (VIN) number from the vehicle identification plate, as well as the mileage and hours on the vehicle.

These steps consist of external inspections and observations that will be valuable when combined with the results of the parts examination.

Look for leaks, cracks or other damage that can point to the cause of the failure.

Make note of obvious leaks around plugs and seals. A missing fill or drain plug would be an obvious cause for concern.

Look for cracks in the carrier housing (harder to see, but sometimes visible).

Does the general mechanical condition of the vehicle indicate proper maintenance or are there signs of neglect?

Are the tires in good condition and do the sizes match?

If equipped with a torque-limiting device, is it working properly?

During the preliminary investigation, write down anything out of the ordinary for later reference. Items that appear insignificant now may take on more importance when the subassemblies are torn down.

After the preliminary investigation, locate the failure and prepare the part for examination. In carrier failure analysis, it may be necessary to disassemble the unit.

When disassembling subassemblies and parts, do not clean the parts immediately since cleaning may destroy some of the evidence.

When tearing down the drive axle, do it in the recommended manner. Minimize any further damage to the unit.

Ask more questions when examining the interior of the carrier. Does the lubricant meet the manufacturer specifications regarding quality, quantity and viscosity? As soon as you have located the failed part, take time to analyze the data.

Here begins the real challenge to determine the exact cause of the failure. Keep in mind that there is no benefit to replacing a failed part without determining the cause of the failure.

For example, after examining a failed part and finding that the fail- ure is caused by a lack of lubrication, you must determine if there was an external leak. Obviously, if there is an external leak, just replacing the failed gear is not going to correct the situation.

Another important consideration is to determine the specific type of failure which can be a valuable indicator for the cause of failure. The following pages show different types of failures and possible causes. Use this as a guide in determining types of failures and in correcting problems.

Once the cause of the problem has been determined, refer to the appropriate service manual to perform the repairs.

Wash steel parts with ground or polished surfaces in solvent. There are many suitable commercial solvents available. Kerosene and diesel fuel are acceptable.

WARNING: Gasoline is not an acceptable solvent because of its extreme combustibility. It is unsafe in the workshop environment.

Wash castings or other rough parts in solvent or clean in hot solution tanks using mild alkali solutions.

If a hot solution tank is used, make sure parts are heated thoroughly before rinsing.

Rinse thoroughly to remove all traces of the cleaning solution.

Dry parts immediately with clean rags.

Oil parts.

If parts are to be reused immediately: Lightly oil. If parts are to be stored: Coat with oil, wrap in corrosion resistant paper and store in a clean, dry place.

Axle housing inspection and repairs are limited to the following checks or repairs.

Visually inspect axle housing for cracks, nicks and burrs on machined surfaces.

Check carrier bolt holes and studs for foreign material.

Replace damaged fasteners. Look for loose bolts or cross-threaded holes.

Any damage which affects the alignment or structural integrity of the housing requires housing replacement. Do not repair by bending or straightening. This process can affect the material’s properties and cause it to fail completely under load.

Check all seals and gaskets.

Replace conventional gaskets with silicone rubber gasket compound (included in many repair kits). The compound provides a more effective seal against lube seepage and is easier to remove from mating surfaces when replacing parts.

Inspect all steel parts for:

Notches, visible steps or grooves created by wear.

Pitting or cracking along gear contact lines.

Scuffing, deformation or discolorations. These are signs of excessive heat in the axle and are usually related to low lubrication levels or improper lubrication practices.

In addition, inspect the following for damage:

Differential gearing.

Bearings for loose fit on drive pinion, and differential bearings.

All fasteners for rounded heads, bends, cracks or damaged threads.

Inspect machined surfaces of cast or malleable parts. They must be free of nicks, burrs, cracks, scoring, and wear.

Look for elongation of drilled holes, wear on surfaces machined for bearing fits and nicks or burrs in mating surfaces.

Before reusing a primary gear set, inspect teeth for signs of excessive wear. Check tooth contact pattern for evidence of incorrect adjustment.