Chevrolet 70 Series 1970, Service Manual

Page: 619 / 841

TRANSMISSIONS AND CLUTCHES 7-20
d river technique, or fa ilu r e to control engine speed
drop-off during upshift, o r failu re to bring engine
sp eed n early tip to governor speed when down­
shifting, c a u se s overw ork of syn ch ron izer and
fa ilu re to sh ift. A lso , d r iv er s who try to shift with­
out using the clutch w ill burn or w ear out manual
sy n ch ro n izers at r ela tiv ely low m ileage.
OIL LEAKS
1. O il le v e l too high.
2. Wrong lubricant in unit.
3. N on -sh ield ed bearing u sed at front or rea r
bearing cap (where applicable).
4. S e a ls (if used) d efective or om itted from
bearing cap, wrong type s e a l u sed , etc.
5. T ra n sm issio n breather om itted, plugged
in tern ally, etc.
6
. Cap sc r e w s lo o se , om itted o r m issin g from
rem ote control, sh ifter housing, bearing cap s,
p ow er tak e-off, or c o v e r s, etc.
7 . W elch "seal" p lu gs lo o se or m issin g en­
tir e ly from m achine openings in ca se .
8
. O il drain-back openings in bearing caps or
c a s e plugged with varnish, dirt, covered with g a s ­
ket m aterial, etc.
9 . Broken g a sk e ts, g a sk ets shifted o r sq u eez­
ed o u t-o f-p o sitio n , p ie c e s s till under bearing caps,
clutch housing, pow er tak e-off, c o v e r s, etc.
10. C racks or h oles in ca stin g s.
11. D rain plug lo o se .
BEARING FAILURES
M ore than 90% of a ll bearing fa ilu r e s a re
cau sed by dirt which is alw ays ab rasive.
D irt may enter the b earings during assem b ly
of the u n its or be ca r rie d into the bearing by the
lubricant w hile in s e r v ic e . D irt may enter through
s e a ls , b reath er o r even dirty containers u sed for
addition o r change of lubricant.
Softer m aterial such a s dirt, dust, e tc ., usually
fo rm ab rasive p a ste or lapping compounds within
the b earin gs th em selv es sin c e the unit p r e ssu r e
betw een the b a lls and racew ays m akes a p erfect
p u lv e r iz e r . The rollin g m otion tends to entrap and
hold the a b r a siv e s. A s the b a lls and racew ays
w ear, the b earin gs becom e n o isy . The lapping
action tends to in c r e a se rapidly a s the fine ste e l
from the b a lls and rollway adds to the lapping
m aterial.
Hard c o a r se m aterial su ch as ch ip s, e tc ., may
enter the b earings during a ssem b ly from h am m ers,
d rifts, pow er c h is e ls , e tc ., or be m anufactured w ith­
in the unit during s e r v ic e from raking teeth, etc.
T h ese chips produce sm a ll indentation in b a lls and
r a c e s . Jam m ing of th ese hard p a r tic le s between
b a lls and r a c e s may cau se the inner ra ce to turn
on shaft, or the outer race to turn in the housing.
CORROSION
W ater, acid , and c o r r o siv e m a teria ls form ed
by d eterioration of lubricant, w ill produce red d ish -
brown coating and sm a ll etched h o les over outer
and exposed su r fa ces of r a c e . C o rro siv e oxid es
a lso a ct a s lapping agent.
FATIGUE
A ll b earin gs a r e subject to fatigue and must
be replaced eventually. Your own operating exp er­
ien ce w ill dictate m ileage rep lacem en t of b earings
showing only norm al w ear.
SHAFTS FITS
E x c e ssiv e lo o se n e ss under load is very ob­
jectionable b ecau se it produces a creeping or
slipping of the inner ring on the rotating shaft.
T h is c a u ses the su rface of shafts to w ear off.
B earin g fits on rotating sh afts a re u sually
sp ecifie d as tight. When play or lo o s e n e s s , even
0
.
0 0 1
", e x is ts betw een the bearing and shaft, there
i s a very powerful fo r c e tending to rotate the inner
ra ce on the shaft; th is fo rce is caused by the lo o s e ­
n e s s o r lo s t motion betw een the p a rts and disap­
p e a r s when no lo o se n e ss e x is ts .
TRANSMISSION REPLACEM ENT-M ANUAL TRANSMISSION
The p roced u res required to rem ove the manual
tr a n sm issio n from v e h ic le s covered by th is manual
a r e dependent gen erally upon the type of cabs (i.e .,
conventional or tilt), type of body, and liftin g equip­
ment available in the rep air shop. O perations other
than those included in th is se ctio n may be n e c e s ­
s a r y if the veh ic le has sp e c ia l equipment such a s
a pow er tak e-off unit and co n tro ls, etc.
The required operations w ill be obvious upon
v isu a l inspection of the v eh icle. The in stru ction s
contained h erein under "Removal" and "Install­
ation" w ill s e r v e a s a guide in accom plishing
tr a n sm issio n replacem ent.
It is im portant to note that v e h ic le s covered
by th is manual w ill have eith er an "Apron" or
"S.A.E. #2" type flyw heel housing a s shown in fig ­
ure 1. The "Apron" type flyw heel housing is ea sily
id entified by the sh eet m etal pan w hich c o v e r s the
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL