• Allows installation of a Hydroboost unit so you can have power-assisted brakes on a Fox Mustang with an engine swap that leaves no room for a vacuum booster. No need to settle for manual brakes!
• Provides excellent brake response and consistent pedal feel regardless of the engine vacuum.
• Low pedal effort, even with small-diameter brake rotors.
• Mounts the Hydroboost unit/master cylinder and the brake pedal arm in the correct relationship to function as it was originally designed.
• Provides the same pedal feel (effort and travel) as a stock 1996-1998 Mustang GT or Cobra, when 1994-1996 GT front and rear brakes or 1994-1996 Cobra front and rear brakes are used, and matched with the corresponding 1996-1998 Mustang master cylinder.
• No modifications needed to the Hydroboost unit, making future service and replacement easy.
• Firewall Adapter Block bolts to the firewall, with only minor firewall modifications needed. It's still easy to return the car to stock.
• We include a new billet aluminum pedal box spacer to ensure your Hydroboost installation project isn't stopped in its tracks while you try to repair the stock plastic spacer you didn't know was broken until your Mustang was taken apart.
• Pedal pad location can be adjusted to suit the driver.
• Includes the socket required to tighten the giant nut securing the Hydroboost to the MM Firewall Adapter Block.
• Includes a special tool to easily and quickly modify the upper edge of the hole in the firewall for pushrod clearance.

• MM's billet aluminum Firewall Adapter Block mounts the Hydroboost unit at the correct angle, height, fore/aft location, and lateral location.
• 4 mounting studs on the Firewall Adapter Block match the Fox firewall hole pattern.
• MM Brake Pedal Arm is made of high-strength alloy steel, with the pushrod pin in the correct location to match the brake pedal ratio and pushrod geometry of a 1999-2004 Hydroboost Mustang.
• MM Brake Pedal Pad is adjustable to suit different driver preferences.
• Billet aluminum MM Pedal Box Spacer replaces the breakage-prone stock plastic spacer.
• Includes MM Socket to tighten the giant nut securing the Hydroboost unit.
• MM special tool to modify the firewall.
• Retains stock brake light switch.

The Mustang Hydroboost units and master cylinders can be difficult to tell apart. The photos below illustrate the differences between them. You need to know which Hydroboost unit and which master cylinder you have in order to get the correct conversion kit and brake line kit.

1996-1998 Master Cylinders

1999-2004 Master Cylinders

• 1979-1993 Mustang
• 1999-2004 Ford Mustang Hydroboost unit

For compatible brake systems, see the list below.

• 1996-1998 Ford Mustang Hydroboost unit
• Any other Hydroboost unit
• 1994-2004 Mustang
• MM Strut Tower Braces MMSTB-1 and MMSTB-2

See the Parts ID tab for photos to help identify your Hydroboost unit and master cylinder.

Hydroboost Compatibility and Brake Bias
MM's Engineering Team has done the math to determine the compatibility of a Hydroboost conversion with many brake systems typically used on Fox Mustangs; see the table below. As a bonus, this table also includes the front/rear brake bias for those systems.

If your Mustang's brake system isn't listed, we can calculate its suitability for a Hydroboost conversion, along with the bias ratio; go to the Technical Services page, select the Fox Hydroboost Conversion option, and follow the instructions.

Ford used brake proportioning valves with the slope and breakpoint pressures optimized for the various Mustang brake systems. This leads to some OEM Mustang exceptions to the general rule that front bias should be somewhere between 70% and 75%. The optimized OEM proportioning valve took care of the baseline bias being out of the preferred range. Aftermarket adjustable proportioning valves have more limited slope options, so it is quite important that the baseline bias be good. MM recommends installing an adjustable brake proportioning valve to fine tune the brake bias whenever any part of the brake system is changed from the stock configuration. Keep in mind that an adjustable valve is only for fine tuning; it cannot make up for a system that is grossly out of front to rear balance.

1. Do NOT use with the early Hydroboost and master cylinder. May be used with the later Hydroboost and master cylinder.
2. For a V8 equipped car, bias only works for a very light front end or a very heavy rear end.
3. Bias works for drag race skinny front tires and very wide rear tires
4. Bias only works for a track car with a very light front end, IRS, and road race stiff suspension.

A quick Internet search will reveal many DIY Hydroboost installations. Also to be found are many failed DIY installs. The MM Hydroboost Swap Kit is designed to solve the problems that cause DIY installations to fail.

Here are some common DIY failure points, and how MM solves them with our well-engineered kit:

The Problem
The pattern of the 4 studs holding an SN95 brake booster (Hydroboost or vacuum) to the firewall and pedal box is different than the Fox Mustang pattern.

The DIY attempt at solution
Enlarge the holes in the firewall and pedal box to match the car to the Hydroboost stud pattern.

The DIY result
Enlarging the holes is very imprecise, and the Hydroboost will never end up in the correct lateral location to maintain proper pushrod geometry. The result is binding and failure of the Hydroboost unit.

The MM solution
MM's aluminum Firewall Adapter Block has the correct stud pattern to mount directly to a Fox Mustang with no firewall or pedal box modifications. The firewall block positions the Hydroboost for correct alignment of the pushrod with the MM Brake Pedal Arm.

The Problem
The DIY installation of a Ford Hydroboost seems daunting. The fabrication required to create one's own "kit" is beyond the skill set of many DIYers.

The DIY attempt at solution
A Web search for a bolt-in kit finds one advertised as bolt-in, no modifications required to the firewall, and no need to change the Fox pedal arm. Best of all, the ad claims "great brakes" because the kit will "create up to 2,500 PSI of brake fluid pressure."

• No mention of pedal ratio. Stating there is no modification to the Fox pedal arm or to the location of the Hydroboost on the firewall means the kit does not have the pedal ratio optimized for the Hydroboost. The result is poor pedal feel, with high initial effort required to activate the Hydroboost.
• Your Mustang does not need 2,500 PSI of brake fluid pressure. The front tires of a Mustang typically lock up at less than 1,000 PSI. When the system creates nearly three times as much pressure as the brake system can use, the result is extremely sensitive brakes. It takes very little pedal travel to cause heavy braking, making it hard to modulate the brakes.

A quick Internet search will reveal many DIY Hydroboost installations. Also to be found are many failed DIY installs. The MM Hydroboost Swap Kit is designed to solve the problems that cause DIY installations to fail.

Here are some common DIY failure points, and how MM solves them with our well-engineered kit:

The Problem
Both generations of Mustang Hydroboost each have their own pedal ratio. Each requires mounting the Hydroboost unit in exactly the right location to match with a precisely located pin on the brake pedal arm. The SN95 firewall plate does not directly bolt to a Fox Mustang firewall. The pin on the Fox Mustang brake pedal arm is not in the correct location for a Hydroboost pedal ratio. Both items must be located in the correct relationship for the Hydroboost to function properly and not fail prematurely.

• For mounting the Hydroboost to the firewall, they modify the firewall and pedal box to match the Hydroboost stud pattern, or they modify the SN95 mounting plate to match the Fox firewall hole pattern.
• For the pedal pin, they modify a stock Fox arm with a new pin or install an SN95 pedal arm.
• To cope with incorrect alignment of the Hydroboost to the pedal pin, they modify the pushrod.
• They try to eyeball the location of all the components.

• Structural failure of the modified pedal.
• Structural failure of the modified Hydroboost pushrod.
• Incorrect pedal ratio, causing the pedal effort to be too high or too low.
• Incorrect static alignment of the pushrod, causing binding, which leads to poor brake operation and Hydroboost failure.
• Incorrect stroke of the pushrod. Overstroking can damage the Hydroboost and master cylinder. Understroking causes low pedal effort and lots of pedal travel.
• Incorrect dynamic alignment of the pushrod. As the pedal pin moves through its arc, the pushrod angularity changes. Improper angularity affects pushrod alignment, affecting pedal ratio and Hydroboost longevity.
• Incorrect lateral alignment of the Hydroboost unit to the pedal arm. The lateral offset of the Fox vacuum-assisted pedal arm and the SN95 Hydroboost pedal arm are different.
• Failure of the seals in the Hydroboost unit because of damage from the heat caused by welding a modified pushrod back together.

The MM solution
MM designed every component in this kit to accurately locate the Hydroboost and brake pedal to maintain correct pushrod alignment and provide the correct pedal ratio. This required the whole system be designed with extreme precision. To that end, the MM Engineering Team created an accurate 3D CAD model of the Hydroboost unit, firewall, pedal box spacer, pedal box, pedal arm, and pedal pad. We designed components in the computer model to maintain proper pedal pad height, provide the correct Hydroboost pedal ratio, and correctly align all components to each other while also fitting the Fox chassis. This design process also resulted in the early and late Mustang Hydroboost swap kits having different firewall adapter blocks, pedal arms, and tools.

How do I know which Hydroboost unit and master cylinder I have?
See the Parts ID tab. It has photos pointing out the differences between the Hydroboost units, and the different master cylinders. That will help you identify your Hydroboost unit and master cylinder.

What power steering pump should I get?
That depends on what project you're doing. Coyote swap kits typically use the 1996-2004 Mustang modular V8 power steering pump; an excellent choice. If you are installing Hydroboost on a Mustang that has a pushrod engine (5.0L, 351, etc.), the OEM Mustang power steering pump is suitable.

If you are using an aftermarket race pump the flow rate needs to be adjusted to match the Ford pump flow rate. Exceeding the Ford spec for flow rate will cause over-assisted steering and over-boosted brakes. Many of the aftermarket race power steering pumps are based on a GM design; GM pumps have far too much flow for the Ford power steering and Hydroboost.

• Probably. The Hydroboost is just a different type of power assist. You do need to confirm that the Hydroboost master cylinder will supply enough brake fluid to properly operate your brake calipers. Some calipers may have too much piston area for the amount of fluid the Hydroboost master cylinder can supply.
• Look at the list on the Fitment tab for brake systems we have checked.
• Related to proper operation is proper front to rear brake bias. That's also listed on the Fitment tab.
• If your brakes aren't listed, go to the Technical Services page, select the Fox Hydroboost Conversion option, and follow the instructions.

• We do not recommend using braided stainless steel hoses in the power steering system for street applications. These hoses do not have the necessary hydraulic compliance required in a power steering system and as a result may cause the steering system to oscillate in some situations, such as when parking.
• Braided stainless steel hose transmits much more steering pump noise than does standard power steering hose.
• If you insist: use the MM-designed adapter fittings (ST-73) to connect -6 AN hose fittings to the steering rack. That's all we have available at this time; we're working on making the other adapter fittings available.

Why doesn't the MMBAK-20 fit the 1996-1998 Hydroboost?
The earlier Mustang Hydroboost has a different pedal ratio, which requires a different location for the Hydroboost unit and a different brake pedal arm to match.

We're working on FAQs for this product. If you have a question, please use our Contact Us page to email your question. We'll answer your question by return email, and also consider it for possible addition to this FAQ section.

Vehicle brakes are designed as a system. The design goals are to provide short stopping distance, resistance to rear lockup, and good pedal feel (pedal travel and effort). Several critical technical factors interact in the design process, but there's room for variation while still achieving the goals. The trick is to vary them correctly to avoid a bad result.

Critical factors include the mechanical pedal ratio, master cylinder bore diameter and stroke length, front and rear rotor diameters, front and rear caliper piston area, amount of power assist, and pad material friction. All must be chosen to work together in a manner that provides the desired pedal effort and travel, and front-to-rear brake bias, to provide short stopping distance and resistance to premature rear wheel lockup.

Changing one or more parts of the system must be done carefully to avoid unintended consequences. That's why when converting to Hydroboost power assist you need to make sure the rest of the brake system is compatible with the specific Hydroboost you select. There is only 1 master cylinder size available for each generation of Hydroboost. There are far more options available for the other components in the brake system. You need to make sure that the rest of your brake system will work well with the particular Hydroboost unit you install.