How To Set Adjustable Proportioning Valve

Created by Jay Walling / 3 min read
Date Created: 8/19/2022
Last Updated: 12/13/2022

Since the introduction of the Fox Mustang, owners have always wanted upgraded brake setups. When incorporating a rear disc conversion, fine-tuning is needed for the rear brake bias. This is where an adjustable proportioning valve comes into place.

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To begin, If any brake components have been recently changed, ensure all air has been properly bled from the system. Also, ensure that the tires on your vehicle are properly inflated to the manufacturer's specifications. For the best results, have a friend with you and ensure you are in a safe area where you can make repetitive stops from 30 MPH to 0 MPH. Normally, a parking lot or a gravel road works best here. Also, ensure you have half of a tank of fuel, no passengers in the car, and minimal loose items in the vehicle's cabin.

Adjustment Procedure

  • Screw the adjustment knob completely out (Counter Clockwise).
  • Accelerate to approximately 30 MPH, then apply the brakes hard enough to lock up the wheels.
  • Have your friend watch (from a safe distance) and confirm that the front and rear wheels lock.
  • If only the front locked, adjust the knob in two full turns to allow more pressure to the rear brakes and test again.
  • Continue adjusting the knob in two turns at a time until the front and rear wheels lock in a hard stopping condition.
  • Adjust the knob out one complete turn and test this procedure again.
  • Continue these adjustments 1/4 to 1/2 turn in or out at a time until maximum braking can be achieved and no wheel rear lock is observed.
  • Test the vehicle again at 50 MPH to judge the effects of a more dramatic weight transfer and make any additional adjustments as needed. Typically this is achieved by turning the knob out to decrease pressure to the rear brakes.

TECH NOTE: When bleeding your brakes, it can be helpful to turn the proportioning valve all the way in to make bleeding easier. Make a note of how many rotations it takes to fully in, then adjust back out the same amount when finished with bleeding.


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Ford mustang Adjustable Proportioning Valves

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About the Author

Jay has written content for Late Model Restoration for over 10 years, producing over 120 articles. Jay has an extensive 25-plus-year background in automotive and is a certified Ford Technician. Read more...