Brake Pressure Regulator - Everything you need to know

Here it is folks, your one stop shop for everything you need to know about the Porsche 914's infamous brake pressure regulator. In this tech article, we'll be going over the function of the pressure regulator, the differences between a pressure regulator and a traditional proportioning valve, and the process and parts needed to rebuild yours at home if you're a DIYer.

What is a pressure regulator?

You can think of the pressure regulator as the grandfather of ABS. It's an early fully mechanical brake safety feature found in the Porsche 914, as well as many other contemporary sports cars (BMW E9, Alfa Romeo Spider etc.). It's designed to keep the car stable under hard braking by making sure the rear wheels never lock up. Porsche was really looking out for the safety of 914 owners by including the regulator in their design, as locking the rears in a mid engine car is almost always catastrophic.

How does it work?

The brake pressure regulator has one simple function that completely changes the braking mechanics of the 914 chassis. When you stomp on the pedal in your 914, pressure is transmitted uniformly to the front and rear brake calipers. As pressure continues to build, a point is reached where the pressure regulator begins to prevent this even distribution. The regulator limits pressure to the rear calipers while maintaining full pressure to the front, making sure the rears cannot lock and send your car spinning. It's important to keep the regulator well maintained as a faulty regulator can stick open or closed. An open regulator will never reduce pressure to the rear calipers, which can cause an unexpected lockup. A closed regulator can permanently reduce rear braking force by 30%.

"Really? It's Not a Proportioning Valve?"

You may read the above description of the pressure regulator and think "isn't that just a proportioning valve?" The answer: a resounding NO. A brake proportioning valve takes the pressure being pushed through your system, and divides it front to rear, with an adjustment functionality. These are used to adjust the bias of your car's braking in the rear to balance mechanical adjustment (larger brake pistons pads, etc.) on a car with a modified braking setup. When you think about it, a proportioning valve can only "limit" your stock 914's braking abilities by limiting fluid to the rear. We don't want that! The pressure regulator allows full pressure initial pressure to both the front and rear, then limits pressure to the rear when you near the lock up point. This key difference between limiting the pressure when necessary versus always limiting pressure is the biggest difference between a pressure regulator and a standard proportioning valve.

Pressure Regulator Maintenance

Now that you've read up on the pressure regulator and what it does, you likely want to make sure yours is working in top form. Luckily for you, pressure regulators are well supported and easy to work with.

If you're interested in having our team of experts do the service for you, with all the factory zinc plating restored, factory green resin on the nuts, and our unparalleled 10 year warranty, you can find the service for early cars (vin range <47429 15751) here, and the service for late cars (vin range >47429 15751) here.

Rebuilding the regulator at home.

If you're a DIYer, you're in luck as well, we offer a full rebuild kit including the proprietary conical tool that makes getting some of the tricker O-rings into the body a breeze. The rebuild kit can be found here

To rebuild the regulator correctly, follow the following steps:

Remove the pressure regulator from your car. You'll find it mounted on the firewall.
Completely disassemble the regulator being sure to keep all the hard parts not included in the rebuild kit safe for reuse.
Remove all old seals on the valve, be careful not to mar the seating surface during removal.
Lube the installation cone with a silicon brake lubricant. This will allow the seals to easily slide onto the valve body.
Place the seals onto the shaft, skirt facing down. Use a pick to stretch the seal, and "hula hoop" the seal down into the proper journal on the valve body.
Put the remaining small O-ring on top of the valve in the smallest journal. Lightly lubricate the valve and place it into the body of the pressure regulator.
Place the large o-ring on the 32mm hex cap. Screw the cap back onto the regulator valve body.
Place the body of the regulator in a vise, and use a 32mm wrench to tighten the cap as tight as you can.
Turn the valve body upside down and install the gasket.
Place tall hat on the bottom of the valve body. Add spring. Add short hat upside down into spring (surface is cupped inwards to the spring).
Assemble the 17mm nut on the adjuster screw, and adjust the nut accordingly.
Screw the assembly into the spring housing leaving space for epoxy and final adjustment.
Mix and lay epoxy underneath the nut. Screw the nut on, and re check that your adjuster nut is still correctly positioned.
Place the spring housing onto the valve body.
Install the mounting bracket, making sure the bracket is positioned correctly.
Place new screws and lock washers through the mounting bracket and spring housing.
Using a press, press the spring housing into the valve body. Make sure all components stay in alignment as the housing mates to the body.
Gently thread the screws into the valve body
Remove from press, and torque all screws down to 15ftlbs.

Congratulations, you've just rebuilt your pressure regulator! Your car will thank you, and you'll thank yourself when you don't go spinning into the outfield of a track, or into a telephone pole or tree on the street.

Got any questions? Feel free to call us at (855) 786-7101 or shoot us an email at support@pmbperformance.com