3–16 Copyright © 1996 General Motors Corp.
AT 500, 1500 SERIES AUTOMATIC TRANSMISSIONS
d. Stall Test Procedures — Vehicles With
Smoke-Controlled Engines
NOTE:
Because smoke controls and throttle-delay mecha-
nisms inhibit engine acceleration, the stall testing may
need to be performed while the vehicle is moving.
(1) Locate an isolated area to perform the
driving stall test.
(2) Select a hold range that will limit road
speed (usually 2nd or 3rd range).
(3) Operate the engine at full throttle, maxi-
mum governed rpm.
(4) Slowly depress the vehicle service brakes
while staying at full throttle.
(5) When the vehicle comes to a stop, record
the engine rpm — this is stall speed.
(6) Proceed immediately with Paragraph e
— Cool-Down Check.
e. Neutral Cool-Down Check Procedure
(1) The neutral cool-down check determines
if the transmission fluid cools properly following an
engine load condition. Perform this check immediately
after the engine speed has been recorded in the stall
test.
(2) Record the converter-out fluid temperature.
(3) With the transmission remaining in N (Neu-
tral) or P (Park), run the engine at 1200–1500 rpm for two
minutes to cool the fluid.
(4) At the end of two minutes, record the con-
verter-out fluid temperature. Converter-out fluid tem-
perature should return to within the normal operation.
f. Results
NOTE:
Environmental conditions, such as ambient temper-
ature, altitude, engine accessory loss variations,
etc., affect the power input to the converter. Under
such conditions, a stall speed deviation up to ±150
rpm from specification can be accepted as within
normal range.
(1) If the engine stall speed is more than 150
rpm below the stall speed specified by the engine man-
ufacturer, an engine problem is indicated, such as the
need for a tune-up.
(2) If the engine stall speed is more than 150
rpm above specification, a transmission problem is in-
dicated, such as slipping clutches, cavitation, or torque
converter failure.
(3) An extremely low stall speed, such as 33
percent of the specified engine stall rpm, during which
the engine does not smoke, could indicate a free-
wheeling torque converter stator.
(4) If the engine stall speed conforms to
specification, but the transmission fluid overheats, re-
fer to the cool-down check. If the fluid does not cool
during the two-minute cool-down check, a stuck
torque converter stator could be indicated.
(5) If the engine stall speed conforms to
specification and the cool-down check shows that
transmission fluid cools properly, refer to Table 3–12,
Section C for troubleshooting procedures.
3–15. PRESERVATION AND STORAGE
a. Storage, New Transmissions (prior to instal-
lation). New transmissions are tested at the Allison
factory with preservative oil and drained prior to ship-
ment. The residual oil remaining in the transmission
provides adequate protection to safely store the trans-
mission for up to one year (stored inside in conditions
of normal climate and with all shipping plugs in-
stalled) without further treatment.
b. Preservation Methods. When the transmis-
sion is to be stored or remain inactive for an extended
period (one or more years), specific preservation meth-
ods are recommended to prevent damage due to rust,
corrosion, and organic growth in the oil. Preservation
methods are presented for storage with and without
transmission fluid.
c. Storage, One Year — Without
Transmission Fluid
(1) Drain the transmission fluid.
(2) Spray two ounces (60 milliliters) of
VCI #10 through the fill tube.
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