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If you are talking about the thing on your frame under the master cyl., it is not a port. valve. That is an equalizing valve in case one brake circuit fails, it shuts it off. Your master cyl. acts as the proportional valve on the 4 wheek drum brakes.
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Slideshow: The VelociRaptor Expedition gains a lift, upgraded suspension, Brembo brakes, and trail-ready equipment while retaining the stock 440-horsepower EcoBoost V6.
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