Pontiac FIREBIRD 1972 Service Manual page 872

FOUR-SPEED MUNCIE TRANSMISSION 7D-3
a. Check clutch adjustments. 3. Worn or damaged shifter shaft seals.
b. Check for dragging or distorted clutch driven 4. Case cover loose or gasket damaged.
plate.
5. Rear extension-to-rear bearing retainer gasket da-
c. Check for tight or frozen clutch gear bearing. maged.
LEAKS LUBRICANT
6. Rear bearing retainer-to-case gasket damaged.
7. Rear extension oil seal worn or damaged.
1. Excessive lubricant.
8. Countershaft loose in case.
2. Clutch gear bearing retainer loose or cracked and/or
gasket damaged.
GENERAL DESCRIPTION
The Muncie four-speed transmission is an optional, heavy-
duty, floor shift, four-speed manual transmission used on
400 and 455 cu. in. engine, A and F Series.
This four-speed transmission (Fig. 7D- 1) consists of two
basic sections: the transmission case, or forward section,
and the case rear extension, or rear section. The forward
section contains the four forward speed gear assemblies
and their synchronizing mechanisms; the rear section con-
tains the reverse gear assembly.
Gearshifting is manual through a floor-type gearshift lever
which activates shift control rods connected to the trans-
mission cover shifter levers for first through fourth gears
and to the reverse lever located in the rear extension. The
shifter lever to the rear of the transmission cover controls
the 1st and 2nd speed gears, while the lever to the front
controls the 3rd and 4th speed gears.
All four forward gears are provided with synchronizing
clutches which can be engaged while the car is in motion.
For 400 cu. in. engine models, gear ratios of 2.52 (first),
1.88 (second), 1.46 (third), 1.00 (fourth) and 2.59 (reverse)
provide excellent ratio matching with minimum loss of
engine speed at the shift points. Reverse gear is not syn-
chronized; therefore, vehicle should be brought to a com-
plete stop before engaging reverse gear.
Special close ratio transmissions are also available for 400
and 455 cu. in. engine models. These are gear ratios of 2.20
(first), 1.64 (second), 1.28 (third), 1.00 (fourth) and 2.27
(reverse).
The transmission may be used as an aid in decelerating by
downshifting in sequence without double clutching or
gear clashing, due to all forward speeds being synchro-
nized.
For all models, the steering column lock requires that the
transmission be in "Reverse" gear before the ignition key
may be removed.
Also, the clutch safety switch will not permit engine
cranking unless the clutch pedal is depressed far enough
to completely disengage the clutch.
A transmission controlled spark (TCS) switch is screwed
into the boss of the 3rd
&
4th shifter shaft opening of the
transmission side cover (Fig. 7D-2). This TCS switch is
closed in all but high gear, grounding an electrical circuit
from the distributor and engine thermo-switch through a
solenoid valve. This closing or grounding of the TCS
switch will retard the spark.
When the transmission is shifted into high gear, the pivot-
ing of the 3rd & 4th shifter shaft will cause the TCS switch
to open, so that the transmission will no longer affect the
vacuum advance of the distributor. See Section 6D for
further details.
DESIGN
The four-speed transmission incorporates helical gears
specially designed to provide high torque capacity without
additional weight and gear teeth proportioned to operate
at high speeds with neither excessive heat generation nor
excessive frictional losses. Shafts, bearings, high capacity
synchronizers and other precision parts are held to close
limits, providing proper clearances necessary for durabil-
ity during extended heavy usage.
Seven basic gears are utilized in this transmission. They
are: main drive gear, 3rd speed gear, 2nd speed gear, 1st
speed gear, reverse gear, countershaft gear and reverse
idler gears (front and rear) (Fig. 7D-1).
The front end of the main drive gear is piloted in a single
row, prepacked and shielded ball bearing mounted in the
engine crankshaft, while the rear end is supported by a
heavy-duty ball bearing located at the front end of the
transmission case.