Gear oil compositions including a first oil basestock and a second basestock. The first basestock includes a Group II bright stock having a kinematic viscosity (ASTM D445, 40 C.) of from 250 mm.sup.2/s to 600 mm.sup.2/s, a kinematic viscosity (ASTM D445, 100 C.) of from 20 mm.sup.2/s to 70 mm.sup.2/s, a viscosity index (ASTM D2270) of from 80 to 120, and a pour point (ASTM D97) of from 50 C. to 20 C. The second basestock includes a polyalphaolefin (PAO) basestock having a kinematic viscosity (ASTM D445, 40 C.) of from 500 mm.sup.2/s to 3500 mm.sup.2/s, a kinematic viscosity (ASTM D445, 100 C.) of from 60 mm.sup.2/s to 300 mm.sup.2/s, a viscosity index (ASTM D2270) of from 150 to 250, and a pour point (ASTM D97) of from 50 C. to 20 C.

Gear oil compositions including a first oil basestock and a second basestock. The first basestock includes a Group II bright stock having a kinematic viscosity (ASTM D445, 40 C.) of from 250 mm.sup.2/s to 600 mm.sup.2/s, a kinematic viscosity (ASTM D445, 100 C.) of from 20 mm.sup.2/s to 70 mm.sup.2/s, a viscosity index (ASTM D2270) of from 80 to 120, and a pour point (ASTM D97) of from 50 C. to 20 C. The second basestock includes a polyalphaolefin (PAO) basestock having a kinematic viscosity (ASTM D445, 40 C.) of from 500 mm.sup.2/s to 3500 mm.sup.2/s, a kinematic viscosity (ASTM D445, 100 C.) of from 60 mm.sup.2/s to 300 mm.sup.2/s, a viscosity index (ASTM D2270) of from 150 to 250, and a pour point (ASTM D97) of from 50 C. to 20 C.

The present invention provides a magnetic viscous fluid and a mechanical device with both improved drag force during excitation and improved rubber-resistant properties. The magnetic viscous fluid comprises a magnetic particle and base oil, wherein the base oil comprises ester base oil and non-polar base oil, and a non-polarity index of the base oil is in the range of 10 to 45.

The present invention provides a magnetic viscous fluid and a mechanical device with both improved drag force during excitation and improved rubber-resistant properties. The magnetic viscous fluid comprises a magnetic particle and base oil, wherein the base oil comprises ester base oil and non-polar base oil, and a non-polarity index of the base oil is in the range of 10 to 45.