Spicer Tandem Drive Axles Service Manual D170, D190, and D590 Series - Manual (Page 8)

4
Inspection
Failure Analysis
Failure analysis is the process of determining the original
cause of a component failure in order to keep it from
happening 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.
How to Diagnose a Failure
The following five steps are an effective approach to good
failure diagnostics.
1. Document the problem.
2. Make a preliminary investigation.
3. Prepare the parts for inspection.
4. Find the cause of the failure.
5. Correct the cause of the problem.
Document the Problem
Here are some guidelines for starting to learn about a failure.
• Talk to the operator of the truck.
• Look at the service records.
• Find out when the truck was last serviced.
Ask the following questions:
• In what type of service is the truck being used?
• Has this particular failure occurred before?
• 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 the following questions:
• Was the vehicle operating at normal temperatures?
• Were the gauges showing normal ranges of operation?
• 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.