transmission for lubrication and basic transmission function.
The torque converter is bolted directly to the engine’s crankshaft and spins at engine speed. The hub on the converter has two notches that engage with the transmission’s oil pump to provide constant oil flow and pressure. The oil pump is the heart of the transmission; it supplies oil for cooling, lubrication, and to operate the various internal components for transmission function.
All automatic transmissions contain clutch drums, planetary gears, sprags, or roller clutches, servos, accumulators, bushings, thrust washers, governors, and many have modulators. The basic arrangement of these components varies between models, but the end result is the same. The parts are designed to efficiently and effectively work together to use engine power to propel the vehicle over a wide variety of operating conditions.
The transmission oil pump is driven directly from the rear snout of the torque converter, which is bolted directly to the engine’s crankshaft, so the oil pump operates at engine speed. The oil pump uses a pressure relief valve to keep oil pressure within a specific range for best transmission operation. Oil from the pump is routed through the vehicle’s transmission oil cooler because heat is created in the transmission as well as inside the torque converter. Oil is also routed to various transmission internal components through the valve body at various sequences for gear selection; this helps keep the engine in its most efficient speed/load range over a broad variety of driving conditions.
A pressure regulator valve is used to control transmission oil pump output pressure. The oil pump pictured here is from a TH400; the pressure regulator valve is located on the backside of the oil pump. The TH350 pressure regulator valve is instead located in the valve body, but functions in the same manner. Regardless of the location of the pressure relief valve, the oil leaving the oil pump must overcome spring pressure to maintain flow to the rest of the unit.
The 700-R4 and 4L60 transmissions use a vane-type pump that is also a positive displacement pump. Hardened rings keep the vanes in contact with the outer portion of the pump. The clearance between the pump rotor and vanes is very close within the pump halves. The internal pump gear is also driven directly by the torque converter. Oil is picked up on the suction side of the pump and discharged on the output side. A pressure regulator valve is used in the pump similar to that of the TH400 to control output pressure.
The TH400 and TH350 transmissions use a gear-type oil pump. The inner gear is driven directly by the hub of the engine’s torque converter. Note that the inner gear is offset in the housing. This creates a chamber that moves oil and forces it out of the pump.
Early 700-R4 transmissions used a 6-vane oil pump assembly. This design was upgraded in 1987 to a 10-vane pump, then eventually to a 13-vane pump. The additional vanes do not increase pump output, but were used to smooth the flow of oil leaving the pump. The 10- and 13-vane pump assemblies can be installed into earlier units that originally came with a 6-vane pump. The later units also used greatly improved pump rings, as well as several improvements to the basic design of the pump itself, that increased durability and make it more reliable in long-term service.
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