How To: Make a portable air supply for an automatic transmission test plate. | Ford Explorer - Ford Ranger Forums - Serious Explorations

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How To: Make a portable air supply for an automatic transmission test plate.


Moderator & long time member.
Staff member
Elite Explorer
November 11, 2005
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City, State
Brooklyn, NY
Year, Model & Trim Level
88 89 93 95 96 Aerostars
Automatic transmissions require hydraulic pressure to engage clutch plates, servos, and other parts. There is a tool called an air test plate which could be used to help narrow down a section that is not working properly (or not at all). The valve body channels fluid through passages which look like lines on a map. The air test plate simulates fluid going through these passages by applying a short burst of compressed air to specific locations (just a like a valve body). Here's an example of what an air test plate looks like:

The air test plate should have a gasket behind it to make a leak free connection. The picture below show one made out of heavy duty gasket material:

The air test plate, and gasket in the above picture is for an A4LD transmission. The tool being modified is an air powered drain cleaner which is used to clean a drain in a sink or a bathtub. It could also be used to unclog a heater core. This modified tool could be used for many different purposes, and not just as a tool for testing automatic transmissions. This picture shows the original fitting removed (fragile plastic), and is being tapped to accomodate a small 1/8" brass pipe:

The tool now has a 1/8" NPT thread. A small brass pipe is screwed in along with a tee:

The gauge is an ordinary tire gauge without the front sleeve. The part unscrews from the 1/8" NPT built in fitting. No other modifications are required. The air hose is connected:

Always use teflon tape on all of the connections, and hold one fitting while turning the other one. The blow gun handle with the rubber tip is connected to the other side of the hose:

Here is the completed tool:

The tool is pumped up to 50 PSI:

This tool is now ready to test a transmission.