31
transmission may be safely operated in a forward or reverse range.
Operation at ambient temperatures lower than those shown will require
preheating with auxiliary heating equipment or by running the vehicle with
the transmission in N (Neutral) for a minimum of 20 minutes before
attempting range operation.
RECOMMENDED AUTOMATIC TRANSMISSION FLUID AND
VISCOSITY GRADE — MT 643R TRANSMISSIONS
• Due to the added heat load from the input retarder, MT 643R transmissions
require special fluid considerations. The approved fluids list is more restrictive
than for non-retarder MT 643R transmissions. Also, the fluid change intervals
are shorter than for non-retarder MT 643R transmissions.
• Only high quality, heavy duty diesel engine oils that are approved Allison C-4
fluids with a viscosity of either SAE 30 or SAE 15W-40 are recommended for
use in MT 643R transmissions. For specific name brands, contact the local
Allison Transmission Regional Office.
• Refer to Table 2 for minimum fluid temperatures at which the transmission
may be safely operated with various fluids. Operation at ambient tempera-
tures lower than those shown will require preheating with auxiliary heating
equipment or by running the vehicle with the transmission in N (Neutral)
for a minimum of 20 minutes before attempting range operation.
CAUTION: Disregarding minimum fluid temperature limits can re-
sult in transmission malfunction or reduced transmission life.
Table 2. Operating Temperature Requirements for Transmission Fluid
Viscosity Grade
Ambient Temperature Below Which Preheat
Is Required
Fahrenheit Celsius
SAE 0W-20 –31 –35
DEXRON
®
-III
–22 –30
SAE 10W –4 –20
SAE 15W-40 5 –15
SAE 30 32 0
SAE 40 50 10
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