Chevrolet Light Duty Truck 1973, Service Manual

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CLUTCHES & MANUAL TRANSMISSION 7M-17
MANUAL TRANSMISSIONS
INDEX
General Description....................................................... 7M-17
Theory of Operation...................................................... 7M-21
Synchronizing Mechanism......................................... 7M-21
Synchronizing Operation............................................. 7M-22
Power Flow...................................................................... 7M-24
Service Operations.......................................................... 7M-29
Linkage Adjustment..................................................... 7M-29
Floor Shift Control Lever Replacement............... 7M-29
Transmission Replacement.......................................... 7M-29
Transmission Alignment...............................................7M-33
Rear Oil Seal Replacement........................................ 7M-34
Speedometer Driven Gear Replacement................7M-35
Side Cover Replacement/Repair...............................7M-35
Transfer Case Replacement...................................... .7M-35
Diagnosis............................................................................ .7M-41
GENERAL DESCRIPTION
The three speed synchromesh transmissions used by GM
(Fig. II and 12) are representative of a constant-mesh
transmission design. Fundamental components of these
units are the case, which houses the gears and shaft; the
control cover, which houses the shifter mechanism; and
the various shafts and gears. The input shaft has an
integral main drive gear and rotates with the clutch
driven plate; that is, the shaft rotates all the time the
clutch is engaged and the engine is running. The input
shaft is supported in the case by a ball bearing and at
the front end by an oil impregnated bushing mounted in
the engine crankshaft. The drive gear is in constant
mesh with the countershaft drive gear. Since all gears in
the coutershaft cluster are integral to the shaft, they also
rotate at the time the clutch is engaged. The countergear
is carried on roller bearings at both ends and thrust is
absorbed by thrust washers located between the
countergear and thrust bosses in the case. An anti-lash
plate assembly at the front face of the countergear
provides a constant spring tension between the
countergear and the main drive gear to reduce torsional
vibrations. The transmission mainshaft is held in line
with the input shaft by a pilot bearing at its front end,
which allows it to rotate or come to rest independently of
the input shaft. Its carried at the rear by a ball bearing
mounted in the front face of the extension housing.
Helical gears are incorporated throughout, including
reverse gear. The mainshaft gears are free to rotate
independently on the mainshaft and are in constant
mesh with the countershaft gears. The reverse idler gear
is carried on a bushing; finish bored in place, and thrust
is taken on the thrust bosses of the case.
The transmissions are fully synchronized in all forward
speeds, however, reverse gear is not. The synchronizer
assemblies consist of a hub, sleeve, two key springs and
three synchronizer keys. The snychronizer hubs are
splined to the mainshaft and retained by snap rings.
These assemblies permit gears to be selected without
clashing, by synchronizing the speeds of mating parts
before they engage. Synchronizer assemblies are
discussed separately later in this section.
Four of the transmission gears are rididly connected to
the countergear. These are the driven gear, second-speed
gear, first-speed gear and reverse gear. The engine
driven clutch gear drives the countergear through a
constant mesh countershaft driven gear. The countergear
rotates in a direction opposite, or counter, to the rotation
of the clutch gear. Forward speed gears on the
countergear remain in constant mesh with two non­
sliding mainshaft gears giving first and second speed.
Third speed is a direct drive with the clutch gear
engaged directly to the mainshaft. Forward gears are
engaged through two sliding synchronizer sleeves
mounted on the mainshaft. Engagement of the constant
mesh mainshaft gears to the mainshaft is accomplished
through blocker ring-type synchronizers.
NOTE: The Muncie unit is similar to the
Saginaw design but differs in that it has a
3-1/4 inch center distance between the
mainshaft and countershaft instead of 3
inches, and has larger bearings, gears, input
shaft and mainshaft. Power flow is essentially
the same for both the Saginaw and Muncie
transmissions.
The Muncie Model CH 465 truck transmission (fig. 13)
uses a constant mesh first gear that engages with the
second spped synchronizer sleeve. Second, third and
fourth gears are synchronized. Clutch gears with two
different splines are used, the larger size for 40-60 series
trucks. The clutch gear is supported by a heavy duty ball
bearing. The forward end of the mainshaft is supported
by a loose collar-type bearing inside the clutch gear,
while the rear is carried on a ball bearing in the case.
End play is taken up by the rear flange retaining nut.
The countergear is supported at the rear by a single row
ball bearing which takes the thrust load, and by a roller
bearing at the front. Incorporated in the cover is a ball
pin type interlock which prevents simultaneous engage­
ment of two gears. As one rod is moved, it pushes a ball
out that engages the other two rods to prevent their
movement.
Gearshift levers on manual transmissions are located
LIGHT DUTY TRUCK SERVICE MANUAL