Transmission Oil Pump
Before any transmission noise or vibration troubleshooting is done, the engine and drivetrain must be ruled out. Transmission oil pumps provide fluid pressure for the transmission and torque converter. The valve body regulates, controls, and directs the flow of pressurized transmission fluid. Gear and rotor-type are considered fixed displacement pumps. Most pumps today are variable displacement. This means they vary or change fluid pressure according to demands.
With a fixed displacement pump, the pressure increases with rotational speed, sometimes providing unneeded pressure. With a variable displacement pump, the pressure is allowed to decrease with lesser demand. This saves energy by decreasing output without affecting speed. Transmission pumps are driven directly from the engine through the torque converter. The torque converter housing is mechanically attached to the engine’s crankshaft. This causes the pump to operate whenever the engine is running. This is why a worn or faulty pump makes a whining noise in all gears including park and neutral.
A restricted or clogged transmission filter will make the same whining noise as a faulty transmission pump. This is important when diagnosing a transmission pump or a torque converter. Make sure the filter is not clogged before replacing the pump.
Diagnosing a transmission is the same as anything else; it often ends up being a process of elimination. Begin with the basics and remember if something is not moving, it’s not making a noise. This is important when diagnosing the drivetrain and planetary gearsets. When a vehicle is placed in drive with the wheels held stationary, the entire drivetrain is also held stationary. This can help in eliminating these items as a potential cause of transmission noise.