Pontiac FIREBIRD 1972 Service Manual page 843

7B-4 1972 PONTIAC SERVICE MANUAL
2. Drain plug loose. 7. Oil drain-back openings in bearing retainer or case
plugged with varnish or dirt, covered with gasket
3. Welch plugs loose or missing from machined open-
material, etc.
ings in case.
4. Seals at side cover or extension housing omitted or
8. Broken gaskets, gaskets shifted or squeezed out of
defective.
position, pieces still under bearing retainer, cover,
etc.
5. Extension housing bushing worn, resulting in repeti-
tive oil seal failures.
6. Attaching bolts loose or omitted from bearing retain- 9. Cracks or holes in castings.
ers, side cover, etc.
GENERAL DESCRIPTION
The Muncie three-speed transmission is the optional
heavy duty, floor shift, three-speed manual transmission
used only on the 350 and 400 cu. in. V-8 equipped A
Series.
It is fully synchronized in all forward gears and incorpo-
rates helical drive gears throughout (Fig. 7B-1). Reverse
gear is not synchronized; however, it is a helical gear to
insure quiet operation. While this transmission is very
similar to the present Saginaw three-speed, it has a 3 1/4
inch center distance instead of 3 inches for Saginaw, has
an iron case and has larger bearings, input shaft, main-
shaft and gears. The main drive gear (input shaft) is sup-
ported by a ball bearing at the front end in an oil
impregnated bushing mounted in the engine crankshaft.
The front end of the mainshaft is piloted in a row of
bearing rollers, set into the hollow end of the main drive
gear and is carried at the rear by a bearing mounted in the
front face of the extension housing. The countergear is
carried on a double row of bearing rollers at both ends and
thrust is taken on thrust washers located between the ends
of 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 counter-
gear and the main drive gear to reduce torsional vibra-
tions. The reverse idler gear is carried on a bushing finish,
bored in place and thrust is taken on the thrust bosses of
the case.
Gear shifting is manual through a floor mounted shifter
assembly from a control rod to the outer rear shifter lever
of the side cover assembly for first and reverse gear; and
from a control rod to the outer forward shifter lever of the
side cover assembly for second and third gear. All three
forward gears are fully synchronized and each of these two
synchronizer assemblies consists of a hub, sleeve, two key
springs and three synchronizer keys. The synchronizer
hubs are spliced to the mainshaft and are retained by snap
rings. The transmission may be used as an aid in slowing
vehicle speed in decelleration by downshifting in sequence
without double-clutching or any gear clashing.
OPERATION
The main drive gear (input shaft), 2nd speed gear, 1st
speed gear and reverse idler gear are in constant mesh with
the countergear and the reverse idler gear is in constant
mesh with the reverse gear. With the engine running and
the engine clutch engaged, torque is imparted through the
main drive gear to the countergear. From the countergear,
torque is then imparted to the 2nd speed gear, the 1st
speed gear and the reverse idler gear. The reverse idler
gear imparts torque to the reverse gear.
NEUTRAL
With the engine running and clutch engaged, the main
drive gear turns the countergear. The countergear, in turn,
rotates the 2nd, 1st and reverse idler gears. The reverse
idler gear turns the reverse gear.
In neutral, both synchronizer assemblies are neutrally po-
sitioned and no power will be imparted to the mainshaft.
FIRST GEAR
With the engine running and clutch engaged, the main
drive gear turns the csuntergear. The countergear, in turn,
rotates the 2nd, 1st and reverse idler gears. The reverse
idler gear turns the reverse gear.
In first speed, the 1st & Rev. synchronizer sleeve is moved
forward on its hub to engage the rotating 1st speed gear
and the 2nd & 3rd synchronizer assembly remains posi-
tioned in neutral. Since the 1st & Reverse synchronizer
sleeve is keyed to its hub, and the hub is splined to the
mainshaft, torque is imparted from the rotating 1st speed
gear through the synchronizer sleeve to its hub and hence
to the mainshaft, causing it to rotate in first gear.