Service Manual D__R440, 460, 480, D_R461, 462, 463, 521, 581, 601, 651, 652, 653 Owner manual

7
Failure Analysis
Failure Analysis
Failure Analysis
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 with-
out 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 cus-
tomer 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 know-
ing 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 in-
stalled. 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 fail-
ure 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 un-
related symptoms can point to the cause of the failure.
• Ask: Was the vehicle operating at normal tempera-
tures?
• Ask: Were the gauges showing normal ranges of op-
eration?
• 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 Identifica-
tion Number (VIN) number from the vehicle identification
plate, as well as the mileage and hours on the vehicle.