Chevrolet 70 1969 Series, Shop Manual

Page: 808 / 913

TRANSMISSION AND CLUTCH 7-62
blocking action of the synchronizer and it is this ac­
tion that m akes the operation of shifting a transm is­
sion having synchronizers different from one which
does not have synchronizers.
Upon shifting gears in these synchronized transm is­
sions, the first part of the gearshift lever m ovem ent
brings the blockers into contact. T he blockers
m om entarily prevent further m ovem ent of the shift
lever and pressure exerted by the driver to complete
the m ovem ent is transferred by the blockers to the
synchronizer, providing force necessary to synchronize
the gears being engaged. W hen engaging gears have
reached the sam e speed the blockers autom atically di­
sengage, perm itting gearshift lever m ovem ent to be
com pleted. Therefore, to properly shift a synchronized
transm ission a steady and continuous pressure must
be applied by the driver to the shift lever until shift is
com pleted. U nder norm al conditions this action is ins­
tantaneous.
Som etim es difficulty is experienced in shifting a syn­
chronizer when the vehicle is standing still. This is
caused by the fact that disengagem ent of the blockers
requires relative rotation, and with the vehicle at rest
and with the engine clutch released, there m ay be at
times no relative rotation of the engaging gears.
U nder these conditions the sam e continuous pressure
should be applied to the shift lever and at the same
tim e the clutch should be engaged slightly. This will
give sufficient rotation to unblock the synchronizer
and allow the shift to be com pleted w ithout difficulty.
The m ain drive gear is supported by a single row ball
bearing m ounted in front of the transm ission case.
The m ainshaft is supported at the front by roller
bearings located in pocket end of the drive gear and is
supported at the rear by a single row ball bearing lo­
cated in rear of transm ission case. The countershaft is
supported at the front by roller bearings in front of
transm ission case. The reverse idler cluster gear ro­
tates on two roller bearings.
M AINSHAFT PUMP (PRESSURE ROTOR)
DESCRIPTION A N D OPERATION
Because of increasingly higher engine speeds and ex­
tended periods of high gear operation, positive lubri­
cation of the m ainshaft on heavy duty truck transm is­
sions is definitely required. The C lark 401V transm is­
sion has a m ainshaft pum p that supplies m ainshaft
gear bushings and bearings with adequate oil at all
times.
The pum p does not have gears, springs, valves, and
pipes - the usual pum p elem ents that give trouble or
wear out. The pum p is com posed of three simple
units: pressure pum p rotor, which surrounds and is
driven by the input shaft; a single free floating vane,
confined in the rotor; and a stationary housing, pro­
vided by the input shaft bearing cap which form s an
eccentric bore for the single vane to contact.
The pum p is fed by gravity out of an oil catching
trough cast on inside of the transm ission case. From
the trough, oil runs into the outside diam eter of pum p
where the single van forces oil to center of the input
shaft and through connecting passages into center of
the mainshaft. A t this point, with com bined effort of
pum p pressure and centrifugal force, the lubricating
oil is forced through radial passages into bushing or
bearing area of the m ainshaft gears. T he oil im m e­
diately spreads to all friction surfaces, including
thrust washers and shaft bearings, giving com plete
and instantaneous lubrication to the m ainshaft, or
upper shaft of the transmission. Results received from
the oil pum p are longer transm ission life, high trans­
mission efficiency, and a cooler operating transm is­
sion.
TRANSMISSION OVERHAUL
IM P O R T A N T : C le a n lin e ss is o f ex trem e im p o r­
tan ce a n d a n ab solu te m u st in the repair
a n d o v e rh a u l o f the tran sm ission . Before
a tte m p tin g o v e rh a u l procedures, th o ro u g h ly
clean the exterior o f the tran sm issio n w ith
c le a n in g solven t to pre ve n t dirt or other fo ­
reign m atter from g e ttin g into the g e a r
m e c h a n ism .
DISASSEMBLY OF T RA N SM ISSIO N
INTO SUBASSEMBLIES A N D
M AJO R C O M PO N EN TS
the transm ission. T he transm ission should be overhauled
in sequence described unless only one unit is to be worked
on.
C O N T R O L T O W E R R E M O V A L
N O T E : O n tran sm issio n s h a v in g a con ve n tio n al
g e a rsh ift lever, accom p lish the fo llo w in g proce­
dures:
1. M ove gearshift lever into “ N e u tral” position.
2. Rem ove four bolts and lock washers attaching control
tower to shift bar housing.
3. Lift control tow er assembly straight off shift bar
housing. Rem ove and discard control tow er to hous­
ing gaskets.
Key num bers in text refer to Figure 21 unless otherwise
SHIFT B A R H O U S IN G R E M O V A L
specified.
The following procedures cover com plete overhaul of 1. Remove control top oil baffle (3, fig. 12) if used.
CHEVROLET SERIES 70-80 HEAVY DUTY TRUCK S H O P M A N U A L