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fluid in the subject transmission should be sampled again immediately to verify the
exceeded limit. If verified, the fluid should be changed regardless of time or mileage.
AUXILIARY FILTER
If a condition occurs that introduces debris into the transmission hydraulic system, a
complete cleanup of the cooler and lines is recommended.
Repeated cleaning and flushing may not remove all debris. For models with a retarder,
replace the main cooler. For models without a retarder, install an auxiliary filter in the
cooler-out line (between the cooler and transmission) if such a filter does not already
exist. This filter has already been included in many recently built vehicles. This
recommendation applies whether the transmission is overhauled or replaced by a new
or rebuilt unit.
If any doubt exists about the cleanup of the cooler, replace the cooler.
Consult your nearest Allison Transmission dealer/distributor or the chassis OEM for
detailed filter information and availability.
Table 4. Fluid Oxidation Measurement Limits
Condition Limit
Viscosity ± 25% Change From New Fluid
Carbonyl Absorbance
Total Acid Number (TAN)
Solids
+ 30* Change From New Fluid
+ 3.0** Change From New Fluid
2% By Volume Maximum
* Carbonyl absorbance units/cm
** mg of KOH required to neutralize a g of fluid
CAUTION: DO NOT install an auxiliary filter in the AT 500R or
MT 643R primary cooler circuit. This reduces retarder effective-
ness. An auxiliary filter in the secondary cooler circuit is sufficient.
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