GMC 1986 P-Truck Service Manual page 393

4B-8 REAR AXLE
FRETTAGE
Corrosion set up by small relative movement
of parts with no lubrication.
Replace bearing. Clean related parts. Check
seals and check for proper lubrication.
STAIN DISCOLORATION
Discoloration can range from light brown to
black caused by incorrect lubricant or m ois­
ture.
Re-use bearings if stains can be removed by
light polishing or if no evidence of overheat­
ing is observed.
Check seals and related parts for damage.
Figure 4—Diagnosis Of Tapered Roller Bearings
SMEARS
Smearing of metal due to slippage. Slippage
can be caused by poor fits, lu b rica tio n ,
overheating, overloads or handling damage.
Replace bearings, clean related parts and
check for proper fit and lubrication.
HEAT DISCOLORATION
Heat discoloration can range from faint yel­
low to dark blue resulting from overload or in -
correct lubricant.
Excessive heat can cause softening of races
or rollers. To check for loss of temper on
races or rollers a simple file test may be
made. A file drawn over a tempered part will
grab and cut metal, whereas, a file drawn over
a hard part w ill glide readily with no metal
cutting.
Replace bearings if over heating damage is
indicated. Check seals and other parts.
F-00531