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

8
Failure Analysis
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.
• 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 ne-
glect?
• 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 insignifi-
cant now may take on more importance when the subassem-
blies are torn down.
Prepare the Parts for Inspection
After the preliminary investigation, locate the failure and pre-
pare 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 recom-
mended 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 viscos-
ity? As soon as you have located the failed part, take
time to analyze the data.
Find the Cause of the Failure
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 ex-
ample, after examining a failed part and finding that the failure
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 here is to determine the spe-
cific 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 determin-
ing types of failures and in correcting problems.
Correct the Cause of the Problem
Once the cause of the problem has been determined, refer to
the appropriate service manual to perform the repairs.