GMC 1982 Light Duty Truck Service Manual page 474

4 B 5 -8 REAR A X LE
Fig. 4B5-16--lnstalling Bearings
3. G ear Set Matching N um bers
All drive pinion and gear sets are manufactured and
sold only in matched sets. Both pieces of the set have
a m atching n um ber
combination of a letter and number.
On most pinions, the num ber is usually marked on the
head end. However, on pinions with parallel-sided
splines, the number may be marked on the top flat or
one of the splines.
On the ring gear, the number is usually found on the
front face of the gear, although sometimes it may be on
the gear O.D.
such as " M 2 9 " or any
A gear and pinion which do not have the same
m atching numbers must
Therefore, if either a pinion or a ring gear should
require replacem ent, both m ust be replaced in a
matched set.
4. Pinion Cone Variation N um ber
Each pinion has a Pinion Cone (P.C.) V ariation
N um ber which indicates variations (in thousandths of
an inch) from the nominal mounting distance. This
Pinion Cone Variation N u m b er is necessary because
pinion and gear sets for a specific series of axles cannot
be .manufactured exactly alike, and there may be slight
differences in the Mounting Distance of the individual
gear sets. This P.C. Variation N u m b e r must be used to
modify the Nominal Pinion Gaging Dimension when
using a pinion setting gage or when calculating pinion
cage shim pack thickness.
The Pinion Cone Variation N u m b er (i.e. P.C. 3 or P.C.
-5) is normally found on the pinion head end; however,
it may sometimes be located on a spline of a pinion with
the larger parallel-sided-type splines or on the ring gear
O.D.
The nominal pinion mounting distance is 6 .125 inch
(155.58m m ).
The pinion backlash setting is .005" - .015" (.13 -
.39mm).
not be run together.