The valve body is the control center of the automatic transmission. It contains a maze of channels and passages that direct hydraulic fluid to the numerous valves which then activate the appropriate clutch pack or band servo to smoothly shift to the appropriate gear for each driving situation.

The valves will wear down, the channels can be abraded and become oversized, and the whole valve body unit can become warped. Signs of a bad valve body can be fluid leaks, slipping during gear changes, or even failure to go into gear.

When the lubricant used becomes worn out or leaks out, the metal parts of the transmission valve body rub against each other and wear out, causing tiny metal pieces to find their way into the transmission fluid. The effect of this is that the gears may stick and in turn fail to work as required.