3–4
Copyright © 1996 General Motors Corp.
AT 500, 1500 SERIES AUTOMATIC TRANSMISSIONS
(3) When choosing the optimum viscosity
grade of fluid to use, duty cycle, preheat capabilities,
and/or geographical location must be taken into consid-
eration. Table 3–1 lists the minimum fluid temperatures
at which the transmission may be safely operated. Pre-
heat with auxiliary heating equipment or by running
the vehicle with the transmission in neutral for a mini-
mum of 20 minutes before attempting range operation.
3–8.
TRANSMISSION FLUID AND
FILTER CHANGE INTERVALS
Transmission fluid and filter change frequency is de-
termined by the severity of transmission service and
by the filter equipment installed. Table 3–2 is a gen-
eral guide. More frequent changes may be required
when the fluid is visually contaminated, when opera-
tions are subject to high levels of contamination or
overheating, or if it is determined by fluid analysis
that the fluid is oxidized beyond the limits listed in
Table 3–3.
3–9.
TRANSMISSION FLUID
CONTAMINATION
a.
Examine at Fluid Change.
At each fluid
change, examine the fluid which is drained for evi-
dence of dirt or engine coolant (water). A normal
amount of condensation will emulsify in the fluid dur-
ing operation of the transmission. However, if there is
evidence of coolant, check the cooler (heat exchanger)
for leakage between the coolant and fluid areas. Fluid
in the coolant side of the cooler (heat exchanger) is an-
other sign of leakage. This, however, may indicate
leakage from the engine oil system.
b.
Metal Particles.
Metal particles in the fluid
(except for the minute particles normally trapped in
the filter) indicate damage has occurred in the trans-
mission. When these particles are found in the sump,
the transmission must be disassembled and closely in-
spected to find the source. Metal contamination will
require complete disassembly of the transmission and
cleaning of all internal and external circuits, cooler,
and all other areas where the particles could lodge.
(See application of auxiliary filter, Paragraph 3–9
d
.)
c.
Coolant Leakage.
If engine coolant leaks into
the transmission hydraulic system, immediate action
must be taken to prevent malfunction and possible se-
rious damage. The transmission must be completely
disassembled, inspected, and cleaned. All traces of the
coolant, and varnish deposits resulting from coolant
contamination must be removed. Clutch plates con-
taminated with ethylene glycol must be replaced.
d.
Auxiliary Filter
(Figure 3–4)
(1) If a condition occurs that introduces de-
bris into the hydraulic system, completely clean-up the
cooler and lines.
(2) However, repeated cleaning and flushing
may not remove all debris. For models with retarder,
replace the main cooler; for models without retarder,
installation of an auxiliary filter in the cooler-out line
(between cooler and transmission) is required if such a
filter does not already exist. This requirement applies
whether the transmission is overhauled or replaced by
a new or rebuilt unit.
CAUTION:
Disregarding minimum fluid temperature limits
can result in transmission malfunction or re-
duced transmission life.
Table 3–1. Operating Temperature Requirements
for Transmission Fluid
(Ambient Temperature Below Which Preheat Is Required)
Viscosity Grade
Fahrenheit
Celsius
SAE 0W-20
–31
–35
DEXRON
®
-III
–17
–27
SAE 10W
–4
–20
SAE 15W-40
5
–15
SAE 30
32
0
SAE 40
50
10
(Ref. 13-TR-90.)
CAUTION
:
If excessive metal contamination has occurred, re-
placement of the cooler and replacement of all
bearings within the transmission is recommended.
CAUTION:
For retarder models, do not add an additional
auxiliary filter after a debris-causing condition.