Tech Tips

You Ask, We Answer! Common Brake Questions

unnamed (4)-1

Our team gets asked a lot of brake questions specific to our customers’ situation. We’re always happy to help, and in this edition, we’ll share our answers for frequently asked questions regarding the combination valve, proportioning valve, all wheel drum brakes, and 14” wheel size.

Do I need a combination valve when using 4-wheel drum brakes? How about if I convert to power brakes?

MP Brakes Experts: First, it’s important to understand what a combination valve is and how it works. Combination valves are an essential part of a front disc/rear drum or an all-disc brake setup. The valve includes three critical components.

  • The pressure differential switch/valve is a safety feature that indicates change in pressure and helps the driver move to a safe location to assess any mechanical issues. 
  • The metering valve works with a front disc/rear drum setup to hold off pressure to the front brakes until pressure has been applied to the rear brakes. 
  • The proportion valve works in a panic situation to cut down rear brake pressure and prevent rear brake lock-up. 

I have an all-wheel drum brake setup and don’t plan to convert. Do I still need a combination valve? 

With 4-wheel drum brakes, a valve is not required. The all-wheel drum braking system can receive equal pressure to all four wheels at the same time, so there’s no need to regulate timing of line pressure like there is with a front disc/rear drum or all-disc setup

If using all-wheel drum brakes, a valve is not needed. If you ever decide you want to convert to power brakes, then it’s possible you’ll need a combination valve if disc brakes are being used. Disc brakes anywhere on your vehicle may require line pressure timing, and you’ll need the combination valve. (We go more in-depth on this in the next question.)

 

RELATED:  What’s a Combination Valve, and How Does it Work?

unnamed (2)

 

Does the combination valve need to change when converting from drum brakes to rear disc brakes?

MP Brakes Experts: Knowing what we know about line pressure in a disc-drum setup vs an all-wheel drum setup, the short answer is, it is not necessarily needed to function, but a 4 wheel disc valve is recommended.

A disc-drum combination valve will hold line pressure off from the front brakes for a very short period of time, where in a 4-wheel disc situation, you want the pressure applied equally, just like with 4-wheel drum brakes.

The amount of time is so insignificant, it won’t matter.

RELATED: Disc Brakes vs Drum Brakes: Should I Upgrade the Brakes on My Classic Car?

Will my 14” wheels work when doing a disc brake conversion? What size wheels work best with disc brake conversion kits? 

MP Brakes Experts: We often get asked if our kits are compatible with various wheel sizes. Many classic vehicles of yesteryear came with a standard 14” wheel size. That size evolved to a more common 15” wheel. And some classic car enthusiasts prefer the look of a 16” or 17” wheel.

So, what’s the answer?

Will the brake kit work for my 14” wheel size? 

In some instances, yes. In most instances, no. There are some wheels that have more available space inside the wheel, making it possible to access for your power brakes conversion project.

 

How can I know for sure if the kit will fit my wheel size? 

Our most popular kits include a wheel fit template, which we recommend in order to guarantee the product will be compatible with your vehicle wheel size.

 

RELATED: Will a Disc Brake System Fit My Ride’s Wheels?

To find the wheel fit template for the kit you’re interested in, go to the brake kit product page, and click on “Wheel Fit Template” in the Downloads section.

Didn’t see the answer you needed? Browse our entire list of FAQs or reach out to us with your specific brake questions, and we’ll get back with you shortly!