Copyright © 1996 General Motors Corp. 3–15
PREVENTIVE MAINTENANCE
PREVENTIVE MAINTENANCE
3–14. TRANSMISSION STALL TEST AND
NEUTRAL COOL-DOWN CHECK
a. Purpose
(1) Stall testing is performed to determine
whether a power complaint is due to an engine prob-
lem or transmission malfunction.
(2) Stall speed is the maximum engine rpm
attainable when the engine is at full throttle and when
the torque converter turbine is not moving, or
“stalled.”
(3) During a stall test, compare actual engine
speed at full throttle stall with established vehicle
manufacturer's specifications.
NOTE:
Engine stall point data can be obtained from the ve-
hicle manufacturer or from the equipment dealer
or distributor.
(4) Stall tests are used as troubleshooting
procedures only — do not perform them as general
checks or maintenance.
b. Stall Testing Preparation
(1) Make sure the fuel control linkage goes
to full throttle and does not stick when released.
(2) Check the air induction system for re-
strictions.
(3) Perform a cold check of the transmission
fluid level and adjust as necessary.
(4) Install an accurate tachometer (do not
rely on the vehicle tachometer).
(5) Install a temperature gauge with the
probe in the transmission converter-out (to cooler)
line.
(6) Block the vehicle wheels.
(7) Start the engine and let the transmission
sump warm to normal operating temperature 160–200°F
(71–93°C).
(8) Perform a hot check of the transmission
fluid level and adjust as necessary.
(9) Turn all engine accessories OFF.
(10) Notify everyone to stay clear of the ve-
hicle.
NOTE:
• For vehicles with engines not equipped with
smoke controls, proceed to Paragraph c.
• For vehicles with engines equipped with
smoke controls, skip Paragraph c and proceed
to Paragraph d.
c. Stall Test Procedures — Vehicles Without
Smoke-Controlled Engines
(1) Apply the vehicle parking and service
brakes.
(2) Shift to D (Drive).
(3) Slowly accelerate to full throttle.
(4) When the tachometer levels off, record
the maximum engine rpm attained.
(5) Slowly release the throttle.
(6) Shift to N (Neutral) or P (Park).
(7) Skip Paragraph d and proceed immedi-
ately with Paragraph e — Cool-Down Check.
WARNING!
While conducting a stall check, the vehicle must
be positively prevented from moving. Apply the
parking brake and service brake, and block the
wheels securely. Warn personnel to keep clear of
the vehicle and its travel path. Failure to do so
can cause serious injury.
CAUTION:
Never maintain the stall condition for more than
30 seconds at any one time because of the rapid
rise in fluid temperature. Do not let the con-
verter-out fluid temperature exceed 300°F
(149°C). Do not rely on converter-out fluid tem-
perature to limit stall duration. During stall con-
ditions, internal temperatures rise much faster
than converter-out fluid temperature. Allow the
system to cool between stall checks by perform-
ing the cool-down as described in Paragraph 3–
14e. If the stall test is repeated, do not let the en-
gine overheat.
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