FAQs & Tech Tips


MM News

NASA Racers! MM will support NASA road racers with $1,000 contingency prizes for the American Iron, American Iron Extreme, and Spec Iron at the 2019 National Champions. You must register to be eligible.

New! Read the article Maximum Motorsports Tames Fox & SN95 Mustang Rear Suspensions on FordMuscle.com.

MRT Exhaust! MM now offers premium MRT cat-back exhaust systems for 1996-2004 Mustangs.

New! for Street & Strip Mustangs! Big-bore rear wheel cylinders for 1979-1993 Mustang with 9" drum brakes. Improves braking when running big rear tires and front skinnies, and/or different OEM front brakes.

New! Swapping a Coyote into a Fox Mustang? MM's Hydroboost Conversion Kits allow easy installation of a 1996-2004 Mustang Hydroboost power brake assist unit into a 1979-1993 Mustang.

New! Swapping an IRS into your Fox Mustang? MM makes it easier with a brake line kit made just for this conversion. Bolts-in, with no cutting or flaring of brake lines. Designed to fit standard IRS brake hoses.

New! MM's billet aluminum Pedal Box Spacer for Fox Mustangs. Replace the breakage-prone OEM plastic spacer when converting to manual brakes or Hydroboost.

Canadians! Please read the latest about ordering from Canada/shipping to Canada.

We've posted the parts list and link to the video of MM's Mustang in /DRIVE Tuner car Shootout

Adjustable Brake Proportioning Valve, SAE ports
Actual product may differ from photo.


  • Item # BPV-1
  • Manufacturer: Wilwood


Wilwood Brake Proportioning Valve is used to adjust rear brake bias. It replaces the stock proportioning valve, and is used to fine tune rear brake bias.

Required when major modifications are done to the brake system, such as:

  • Converting from rear drums to discs
  • Increasing rotor size
  • Converting from power-assisted to manual brakes

Desirable for many high performance situations, such as:

  • Mustangs with stiff suspensions
  • Mustangs with sticky tires
  • Autocrossing
  • Open-tracking
  • Road racing
  • Drag racing


The stock brake proportioning valve must always be disabled when installing an adjustable valve. There must be only one valve in the brake system, never two valves. You may disable the stock valve by either of these two methods:

  1. Remove the stock valve with MM's Brake Proportioning Valve Eliminator Kit.
  2. Disable the stock valve by removing the internals and replacing the stock valve's plug with the MM-2450-A solid plug.

Need more information?
Read the FAQ tab.


  • Wilwood states this valve is intended for off-highway application only.
  • Brake fluid will be required when bleeding the brakes after installation.
  • An adjustable valve means that you must adjust your Mustang's brake bias after installation. Do so at low speeds in a safe area.
  • Allows adjusting the hydraulic pressure to the rear brakes.
  • Adjusting the rear line pressure alters the force applied by the rear brakes.
  • Allows adjusting the rear brake torque to better balance the rear brakes with the front brakes.
  • Extremely helpful when swapping brakes from one model/year to another.
  • Designed and manufactured by Wilwood.
  • Has standard SAE threaded ports.
  • Direct fit for inverted flare brake lines with 3/8-24 tube nuts.
  • Direct fit in rear brake line of 1983-1993 Mustang: No adapters needed.
  • Rotating the knob makes the pressure adjustment.
  • Provides infinite adjustment increments.


  • Direct bolt-in fitment to 1983-1993 Mustang.
  • Ports fit 3/8-24 inverted flare tube nuts.
  • Fitment for other Mustang years requires adapter fittings or cutting and flaring of the rear brake hard line.

Do you have a 1994-2004 Mustang?
Use the BPV-3 proportioning valve.

Why would I want to adjust brake bias?

Adjusting the brake balance is usually necessary whenever the brake system is changed significantly, such as by swapping calipers and/or rotors from a different year/model Mustang, or converting to manual brakes. Even modifications such as a stiffer suspension and sticky tires can alter how much rear brake bias a particular car can utilize. Installing a Wilwood Adjustable Brake Proportioning Valve allows you to fine-tune your Mustang's brake balance to optimize the brake bias to match your car's setup.

How does an adjustable valve work?

An adjustable proportioning valve changes the front to rear brake balance by reducing the hydraulic line pressure to the rear brakes, whenever the inlet pressure is above the breakpoint pressure set by the valve adjustment. Below the breakpoint pressure, the rear line pressure will always be the same as the front pressure. Above the breakpoint pressure, the rear line pressure will always be less than the front pressure.

How is the valve installed?

The proportioning valve itself may be mounted in any physical location; it simply needs to be plumbed into the proper line of the brake system. The valve is always placed in the rear brake line, between the master cylinder and the rear brakes, or between the master cylinder and ABS unit on cars with ABS. Depending on the model year, installation may be an easy task, or it may require some ingenuity to accomplish.

The BPV-1 valve comes with the correct 3/8-24 inverted flare fittings for a very easy installation on a 1983-93 Mustang. These model years have a splice-block in the rear brake line, located on the passenger side of the firewall. The adjustable valve can be easily plumbed into the system at that point. The valve may be located there, or additional hard-lines can be used to reach the valve if it is mounted elsewhere.

How do I remove or disable the stock brake proportioning valve?
There are two ways to do so:

  1. Remove the stock valve with MM's Brake Proportioning Valve Eliminator Kit.
  2. Disable the stock valve by removing the internals and replacing the stock valve's plug with the MM-2450-A solid plug.