TM 9-2320-266-34
a Pressure Supply System. The pressure supply system
4-3. Testing the Transmission.
consists of an oil pump driven by the engine through the
a Genera/. Automatic transmission malfunctions can be
torque converter. The single front pump furnishes pressure
caused by four general conditions: Poor engine performance,
for all hydraulic and lubrication requirements.
improper adjustments, hydraulic malfunctions, and mechan-
b. Pressure Control Valves.
ical malfunctions. Begin diagnosing these problems by check-
ing the fluid level and condition, the gear selector linkage
(1) The regulator valve controls line pressure at a value
adjustment, and the throttle linkage adjustment. Then per-
dependent on throttle opening.
form a road test to determine whether the problem has been
(2)The torque converter control valve maintains
corrected or if more testing is necessary. If the problem
torque converter operating pressure and transmission lubri-
exists after the preliminary tests and corrections are com-
cating pressure,
pleted, perform the hydraulic pressure tests.
(3) The governor valve transmits regulated pressure to
b. Fluid Level and Condition.
the transmission. The amount of pressure depends upon
(1) Before removing the dipstick, wipe all dirt from
vehicle speed and helps control upshift and downshift
the protective cap and the top of the filler tube.
speeds.
(4) The throttle valve transmits regulated pressure to
NOTE
the transmission. The amount of pressure depends upon
throttle position and helps control upshift and downshift
Since the torque converter fills more slowly
speeds.
in the "P" (Park) position, place the selec-
tor lever in "N" (Neutral) to be sure that
c. Flow Control Valves.
the fluid level check is accurate.
(1) The manual flow valve provides the different
transmission drive ranges as selected by the vehicle operator.
(2) Idle the engine. The fluid should beat normal
(2) The 1-2 shift valve automatically shifts the trans-
operating temperature (approximately 175 F). Keep the
mission from low to second or from second to low.
fluid level between the FULL and ADD ONE PINT marks
on the dipstick.
(3) The 2-3 shift valve automatically shifts the trans-
mission from second to direct or from direct to second.
(a) Low fluid level can cause a variety of condi-
tions because air mixes with the fluid in the pump. As in
(4) The kickdown valve makes possible a forced down-
any hydraulic system, air bubbles make the fluid spongy;
shift from direct to second, second to breakaway, or direct
therefore, pressures will be low and build up slowly.
to breakaway. Valve operation depends upon vehicle speed
and is initiated by depressing the accelerator pedal past the
(b) Improper filling can raise the fluid level too
detent "feel" near the wide open throttle position.
high. When the transmission has too much fluid, the gears
churn up foam, causing the same conditions which occur
(5) The throttle pressure plug at the end of the 2-3
with a low fluid level.
shift valve, provides a 3-2 downshift with varying throttle
openings depending upon vehicle speed.
(c) In either case, the air bubbles can cause over-
heating, fluid oxidation, and varnish. These conditions inter-
(6) The 1-2 shift control valve transmits 1-2 shift con-
fere with normal valve, clutch, and servo operation. Foaming
trol pressure to the transmission accumulator piston to con-
can also result in fluid escaping from the transmission vent
trol the kickdown band capacity cm 1-2 upshifts and 3-2
where it may be mistaken for a leak.
downshifts.
(3) Be sure to examine the fluid on the dipstick
(7) The limit valve determines the maximum speed at
closely. If there is any doubt about its condition, drain out
which a 3-2 part-throttle downshift can be made.
a sample for a double check. After the fluid has been
(8) The shuttle valve has two separate functions and
checked, seat the dipstick fully to seal out water and dirt.
performs each independently of the other. The first is to
(4) If the fluid smells burned and is contaminated
provide fast release of the kickdown band, and smooth front
with metal or foreign particles, a complete transmission over-
clutch engagement when the driver makes a "lift-foot" up-
haul may be needed. Before overhauling, try draining the
shift from second to direct. The second shuttle valve func-
fluid, changing the filter, adjusting the bands, and refilling
tion is to regulate the application of the kickdown servo and
the transmission (paragraphs 4-9 and 4-1 2).
band when kicking down from direct to second.
(5) If the fluid smells burned, but there is no evidence
d. Clutches, Band Servos, and Accumulator
of contamination, an overhaul is not necessary. In this case,
drain the transmission and refill it in accordance with para-
graph 4-9.
apply the bands. On the 2-3 upshift, the kickdown servo
piston is released by spring tension and hydraulic pressure.
below) and then perform the pressure tests (paragraph 4-4).
(2) The accumulator controls the hydraulic pressure
c. Gear Selector Linkage. Normal operation of the neu-
on the apply side of the kickdown servo during the 1-2 shift.
tral safety switch provides a quick check to confirm proper
This cushions the kickdown band application at any throttle
gear selector linkage adjustment.
position.
4-11
