1997 Plymouth Voyager help

That's the height-sensing proportioning valve.

Proportioning valves limit hydraulic pressure to the rear wheels to prevent wheel lockup under hard braking. The valve is very carefully calibrated for the front-to-rear weight distribution of the vehicle, but on pickup trucks and minivans that can vary greatly depending on how much cargo is being carried. You would lose brake effectiveness with a heavy load or experience easy rear wheel lockup with a light load, so the height-sensing valve is used to adjust the hydraulic pressure for any condition.

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