Spicer Drive Axles Failure Analysis Service Manual - Manual (Page 19)

Failure Analysis
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How to Diagnose a Failure
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 unnec-
essary 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 some cases, the part itself is at fault. In the case of a rebuilt rear axle, mis-
matched gears may have been installed.
The more successful shops prevent repeat equipment failures by developing good failure analysis practices. Knowing how to di-
agnose 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:
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, 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.