I have overdrive pressure gauges already made up as a tool, incorporating an original operating valve plug and a glycerin filled 600 psi gauge ready to fit on the overdrive in place of the operating valve plug. I sell them for $55.50 including shipping in the US. They are invaluable for not only testing the overdrive on a test stand but, more importantly, one can test the overdrive for proper pressure while still in the car!

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