Transmission Fluids

The gears mesh with clearances, so there is no gear to gear contact, the transmission fluid is what touches the gears, remember fluid is not compressible, so the forces are transferred. The clearances are based on the fluid characteristic know as Viscosity. The “weight” of the oil is a measure of the fluids viscosity. The thicker the fluid the lower “weight”, low viscosity. Viscosity is defined as a quantity expressing the magnitude of internal friction, as measured by the force per unit area resisting a flow in which parallel layers unit distance apart have unit speed relative to one another. As temperature goes up, viscosity increases. The frictional forces cause the fluid temperature to increase, to keep the fluid from becoming to viscous and breaking down, it is cooled in a separate section of the radiator.

The difference between gear oil (use GL-4 not Gl-5) and Automatic Transmission (use Dextron) fluid, the AT fluid has detergents and conditioners added to it. Always use the exact fluid recommended and the procedure to fill and measure the correct levels and change fluid at correct intervals. Dark fluid is dirty fluid. The plugs used in the Datsun Transmissions before the FSR90A have tapered plugs. Do not over tighten, you can crack the case, always torque to specs.

Datsun 4 speed manual transmission F4W71B Factory Service Manual Data
Year and Model, Gear Ratios, Oil and Capacity and Speedometer Drive Pinion Gear

Datsun Transmission FW71B USA Factory Service Manual Data from Nissan Motor Corp

Datsun 5 speed manual transmission FS5C71B Factory Service Manual Data
Year and Model, Gear Ratios, Oil and Capacity and Speedometer Drive Pinion Gear

Datsun 5 speed manual transmission FS5C71B Factory Service Manual Data

Datsun 3 speed Automatic Transmission 3N71B Factory Service Manual Data
Year and Model, Gear Ratios, Oil and Capacity, Torque Converter and Stall RPM

Be sure to check service manual for procedure for filling transmission, you may need to fill torque converter with a certain amount of fluid. The Stall RPM is the rpm needed for the vehicle to actually move.

Datsun 5 speed manual transmission FS5R90A Factory Service Manual Data
Year and Model, Gear Ratios, Oil and Capacity and Speedometer Drive Pinion Gear

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