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Bypass Line

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2. The first thing Wood explains to customers is where Ford went wrong when they designed the transmission in the first place. Notice the small "bypass" line on the workbench. This line was designed to allow transmission fluid to reach operating temperature quickly after start-up. Basically, it involves an inline check valve that opens up, allowing ATF to bypass the cooling circuit when restrictions are above a specific value, e.g., cold temperatures, or with the addition of extra transmission coolers and/or increased line pressure. This is bad for those of us who like to improve things over stock. Without proper cooling, ATF quickly degrades, causing internal components to wear prematurely.

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