Sticking Transmission Valves

Cleaning an automatic transmission valve.

A transmission can form tarnish in time or without maintenance. This tarnish coats the case and valve body, affecting valve operation and 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 tarnish from components like the valves, springs, and corresponding bores.

Valves are 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 having the valve body in a vertical position. Many valves are made of aluminum to reduce weight.

Shift valves are switch valves because there are 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 cycling is why a pressure regulator valve can make a buzzing sound when it's worn or faulty.