2009-2011 Honda FourTrax Rancher AT TRX420FA/FPA Service Manual, Page 453Get this manual
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FRONT DRIVING MECHANISMSELECTABLE 4WD SYSTEM
After disassembly
STANDARD 230 cm (7.8 US OZ8.1 Imp oz) 310 cm (10.5 US OZ10.9 Imp oz) Hypoid gear oil, SAE80 0.050.25 (0.0020.010)