Spicer Single Drive Axles Service Manual: S140 Series - Manual (Page 7)

4
Inspection
Inspection
Inspection
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
without determining its cause, there will be a recurring failure.
If a carrier housing is opened, revealing a ring gear with a bro-
ken 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 fail-
ure 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 equip-
ment 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 prac-
tices. Knowing how to diagnose the cause of a premature fail-
ure 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:
1. Talk to the operator of the truck.
2. Look at the service records.
3. Find out when the truck was last serviced.
4. Ask: In what type of service is the truck being used?
5. Ask: Has this particular failure occurred before?
6. 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:
7. Ask: Was the vehicle operating at normal tempera-
tures?
8. Ask: Were the gauges showing normal ranges of
operation?
9. 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 ser-
vice and maintenance records. Verify the chassis Vehicle
Identification Number (VIN) number from the vehicle identifi-
cation plate, as well as the mileage and hours on the vehicle.
Make a Preliminary Investigation
These steps consist of external inspections and observations
that will be valuable when combined with the results of the
parts examination.
1. Look for leaks, cracks or other damage that can
point to the cause of the failure.
2. Make note of obvious leaks around plugs and seals.
A missing fill or drain plug would be an obvious
cause for concern.
3. Look for cracks in the carrier housing (harder to see,
but sometimes visible).
4. Does the general mechanical condition of the vehicle
indicate proper maintenance or are there signs of
neglect?
5. Are the tires in good condition and do the sizes
match?
6. If equipped with a torque-limiting device, is it work-
ing properly?
During the preliminary investigation, write down anything out
of the ordinary for later reference. Items that appear insignifi-
cant now may take on more importance when the subassem-
blies are torn down.