Sticking Transmission Valves
A transmission can form tarnish in time or with a lack of maintenance. This tarnish coats the case and valve body affecting valve operation, causing them to stick in their bores, resulting in a no shift or partial shift situation. Use a cleaning agent and a lint-free cloth to remove it from components like the valves, springs, and their corresponding bores.
Valves are made of steel or aluminum and should slide easily in their bores. They are held in place by caps or plugs. A steel valve should slide out merely by holding the valve body in a vertical position. Many valves are made of aluminum to reduce weight.
Shift valves are considered switch valves, because there's only two positions, and they only move when the transmission shifts gears. There's one shift valve for each upshift. A four speed transmission has three shift valves. The 1-2, the 2-3 and the 3-4. Pressure regulator valves cycle frequently. This is why a pressure regulator valve makes a buzzing sound when it's worn or faulty.