Chevrolet 70 1969 Series, Shop Manual

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TRANSMISSION A N D CLUTCH 7-81
at a higher rpm can introduce vibration frequencies, that
were not critical in the past. A t slower speeds these items
would get by or only pass through critical periods while
accelerating or decelerating through the gears.
b. In the past, drive line vibrations such as bent tubes,
joints out of phase or alignm ent, bad angles due to short
couples, clutches out of balance, gears and shafts in trans­
mission out of balance, were fairly obvious. These items
will becom e m ore critical in vehicles running at sustained
high speeds.
c. Critical vibrations associated with higher speeds are
not the old thum ping or bum ping type, but are high fre­
quency vibrations. This type of vibration will cause gear
seizures, broken synchronizer pins, bearing failure due to
retainer rivet failures, prom ote brinelling, fretting co rro­
sion, etc.
8. G ear W hine is usually caused by lack of backlash be­
tween m ating gears or im proper shim m ing of power
take-off units.
N O IS E IN N EU TRAL
1. M isalignm ent of transm ission.
2. W orn or scored m ain drive gear a n d /o r countershaft
bearings.
3. Scuffed gear tooth contact surfaces on gears.
4. U nm atched constant mesh gears.
5. W orn, rough reverse idler gear.
6. Eccentric countershaft gear assembly.
7. Sprung or worn countershaft.
8. Excessive backlash in constant mesh gear.
9. Excessive end play in countershaft, or reverse-idler
pinion.
10. W orn m ainshaft pilot bearing.
11. Scuffed gear tooth contact surface insufficient lubrica­
tion.
12. Incorrect grade of lubricant.
13. Incorrect clutch linkage adjustm ent.
N O IS E IN G E A R
1. W orn, or rough m ainshaft rear bearing.
2.
Rough, chipped, or tapered sliding gear teeth.
3. Noisy speedom eter gears.
4. Excessive end play of m ainshaft gears.
5. Refer to conditions listed under “ Noise in N eutral.”
W A L K IN G O R SLIP P IN G O U T O F G E A R
1. Spicer transm issions are provided with “ hopping
G u ards” for m ost gear positions. Therefore, if the units
are walking out of gear it could be caused by:
a. Interference or resistance in the shift m echanism
preventing full engagem ent of the sliding clutch
gear, or -
b. If the gear has been shifted completely into
position som e other m alfunction which could
move the gear or the shaft itself out of its proper
location.
2. If rem ote controls are used, the m echanic m ust satisfy
himself that the rem ote units are satisfactory and that
transmission is actually at fault. O ne other point that
should be noted is whether the unit walks out of gear
under drive (while pulling a load) or on a coast load.
Also, does the gear hop occur on sm ooth or only on
rough roads. A num ber of items that would prevent full
engagem ent of gears are:
a. Im properly positioned forw ard rem ote control
which limits full travel forward and backw ard
from the rem ote neutral position.
b. Im proper length shift rods or linkage that limits
travel of control island shift m echanism from neu­
tral position.
c. Loose bell cranks, sloppy ball and socket joints.
d. Shift rods, cables, etc., too spongy, flexible, or
not secured properly at both ends.
e. W orn or loose engine m ounts if forw ard unit is
m ounted to frame.
f. C ontrol island shift m echanism m ount too flimsy,
loose on frame, etc.
g. Setscrews loose at rem ote control joints or on
shift forks inside rem ote or even inside trans­
mission unit.
h. Shift fork pads or groove in sliding gear or collar
worn excessively.
i. W orn taper on gear clutch teeth.
j. Transm ission and engine out of alignm ent either
vertically or horizontally.
3. A few items which could move the gear or shaft out
of proper position, particularly on rough roads are:
a. Use of heavy shift lever extensions.
b. Shift rod poppet springs broken.
c. Shift rod poppet notches worn.
N O T E : W h e n g e a rs h ift lever can b e held in to
prevent ju m p-ou t, deten t m o d ific atio n s w ill
often correct it. W h e n a g e a r h a s bee n a llo w e d
to ju m p out for a lo n g period g e n e ra lly the
c au se m u st be corrected p lus re p lac e m e n t of
the affe cte d ge ars.
d. Shift rod bent or sprung out of line.
e. Shift fork pads not square with shift rod bore.
f. Excessive end-play in drive gear, m ainshaft or
countershaft, caused by worn bearings, retainers,
etc.
g. T hrust washers or faces worn excessively, missing,
etc.
H A R D S H IF T IN G
1. Sliding gear tight on shaft splines.
2. Insufficient cham fer of sliding gear teeth.
3. Burred m ainshaft or sliding gear splines.
4. M isaligned mainshaft.
5. D am aged synchronizing unit.
6. Im proper adjustm ent of shifting linkage or excessively
worn.
7. W orn shift rods.
8. W orn or sprung shift fork.
9.
Synchronizer bronze worn, or steel chips im bedded in
bronze prevent proper synchronization.
10. D am aged synchronizer such as broken poppet springs,
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK S H O P M A N U A L