What to Look for in a Worn Transmission Pump
Before any transmission noise/vibration diagnosis is done the engine and drive train should be ruled out. Check for worn u-joints that can cause a noise at all vehicle speeds. Check for worn mounts that can cause a vibration or cause the transmission to touch the frame or body of the vehicle. Transmission oil pumps provide fluid pressure for the transmission and the torque converter. The valve body regulates, controls, and directs the flow of this pressurized fluid to provide shifting. 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.
Fixed Displacement Pump
In a fixed displacement pump the pressure increases with rotational speed, sometimes providing unneeded pressure. In 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 engines crankshaft. This causes the pump to operate whenever the engine is running. This is why the pump will make a whining noise in all gears including park and neutral.
Plugged Filter or Pump Noise?
A restricted or clogged transmission filter will make the same whining noise as a transmission pump. This is important when diagnosing a transmission pump or a torque converter. A transmission pump makes noise in all gears and is directly related to engine speed.
Torque Converter or Pump Noise?
A torque converter will make the most noise when the vehicle is placed in gear and the wheels held stationary. This is because the turbine is held stationary while the housing is spinning from engine rotation (working the bearing); while in park and neutral the noise is gone because the whole unit is spinning. This rattling noise usually decreases as the vehicle begins rolling forward.
Diagnosing a transmission is the same as anything else and 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 to remember when diagnosing planetary gear sets and the drive train. When a vehicle is placed in drive with the wheels held stationary the entire drive train is also held stationary. This can help in eliminating these items as a potential cause of transmission noise.
Operation of Transmission Valve Body & How to Service it
At the heart of the automatic transmissions hydraulic control system is the valve body. It usually consists of several parts: the separator plate or transfer plate, valves, and the valve body itself. The valve body often consists of two parts, upper and lower separated by a gasket and a separator plate. The valve body is installed onto the transmission as a single unit. It can be constructed of either iron or most likely aluminum.
The different types of valves inside the valve body you will find are:
The poppet valve can be a ball or a flat disc. It typically has a stem that acts as a guide for the valves opening or closing. This valve like so many others acts as a port to either block or allow the flow of fluid.
A check ball valve sits in a seat in the valve body. It allows or blocks fluid flow according to the direction of its flow. These check balls can be either normally open or closed depending on the application and manufacturer.
The spool valve is the most common valve found in automatic transmissions. They resemble a spool of thread with large areas used to block fluid flow called lands and stemmed areas called valleys. At each end of the valve is located a reaction area. This is the area where fluid pressure, linkage, or a spring acts as a force to activate the valve.
Servicing an Automatic Transmission Valve Body
Once removed, the valve body should be cleaned with solvent and should be wiped clean using a lint free cloth only. Clearance between the valve in its bore is typically .001″. If bent, the valve must be replaced. If the valve body’s bore is beyond specifications the valve body is replaced. There are two things that are most common that you’ll find in a worn valve body.
- Worn valves and valve bores
- Stuck or sticky valves and possibly worn valve body springs
When cleaning the valves for being sticky I will use emery cloth or Scotch Bright. Then I will take a small piece of the Scotch Bright and wrap around something like the picture shown. Then I can run it with my drill in and out of all the valve bores. It’s almost like cleaning cylinder bores for a re-ring.
Now, if you see signs of wear on the valves or bores I suggest you look into replacing the valve body or look into valve body update kits. Sonnax makes some really good kits which are way less than replacing the valve body and besides what you will get is most likely the same thing just done by somebody else.