Tech Talk with Master Power Brakes

[Video Guide]: How to Convert Rear Drum Brakes to Disc

Posted by Master Power Brakes Team on Apr 11, 2022 2:34:11 PM

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Have you ever put off a project because you had no idea where to begin, were unsure if it was worth it, or didn’t quite think you could pull it off? 

We get it. 

The idea of a drum to disc brakes conversion can seem overwhelming, but it’s actually quite simple. Our video will walk you through the installation process, plus we’ll go through all the parts you’ll need and cover the most common questions fielded by our Tech Team.


Is it easy to change drum brakes to disc brakes?  


Not much is needed to perform this conversion besides a rear disc brake conversion kit. The kits are designed to make your life easy by providing an all-in-one solution. Make sure you choose a kit that matches the make, model, and wheel size of your vehicle. If you’re unsure about wheel size, you can print out a wheel fitment kit as an option under each respective kit’s product page. 

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Before and after a rear drum to disc brakes conversion.


What all is included in a drum to disc brakes conversion kit? 

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Our 1966 Ford F100 Legend Series Rear Disc Brake Conversion Kit 


The materials used in each kit are based on the make and model of your vehicle and take into consideration performance and driving habits.

Our rear disc brake conversion kits include the following components:

  - Calipers
  - Rotors
  - Brake Pads
  - Caliper Mounting BracketsRubber Brake Hoses (Includes banjo bolts, crush washers and adapters)
  - Stainless Steel Braided Brake Hoses (available upgrade, additional charge)
  - All Grade 8 Hardware Included

For specifics, look at the product description under each kit. 


Is it worth it to convert rear drum brakes to disc brakes? 

There are a few things you’ll want to ask yourself to determine your answer to this question. First, are you unhappy with how your current brakes are performing? Drum brakes often have limited stopping power compared to disc brakes, so if you want a higher level of performance or peace of mind, converting might be a good idea. 

There is a cost investment, but the work required to convert your brakes is not much (see our video again if you need a reminder!). 

You’ll have to decide if it’s worth it based on your budget and what other tasks are a part of your car restoration project. 

If you want a higher level of performance and peace of mind, converting to disc brakes is a good idea.


How much does it cost to convert drum brakes to disc? 

Our kits are priced from $629 with our Legend Series up to $1,370 with our Pro Driver Series

Which kit you choose depends on your vehicle’s make and model, desired performance, driving habits, and budget.

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Pro Driver Series Rear Disc Brake Conversion Kit 

Related: Which Brake Kit Do I Need? Legend, Rallye or Pro Driver? 

In addition to the kit, your standard mechanic’s toolkit should be all you need to get the job done. 

Related: Best Mechanic’s Tool Sets for 2022 

Additionally, you might want a new set of park brake cables (more on that later). 

For maintenance work, like bench bleeding your new master cylinder or bleeding your system, you might find life easier with our proportioning valve bleeding tool and our bleeder syringe tool


Can I use a drum brake master cylinder with disc brakes? 

Guys and gals often ask, “Do you need to change the master cylinder on a rear brake conversion?” 

In short, no.  

99 out of 100 times, there isn’t anything that needs to be changed when discussing the master cylinder in a rear drum to disc conversion. But there are a couple of things to quickly look at to make sure you aren’t that one in a hundred.


Bore Size

Normally the bore size in the master cylinder that worked with the stock wheel cylinders will work with most calipers used in a rear disc brake conversion kit. An instance where it wouldn’t be is if the caliper being used has a very large piston. For instance, some people like to use the non-park brake D154 calipers on the rear. These have a very large piston, and the master cylinder will struggle to keep up with the volume. A change would be required. 


Residual Valves

Another thing to pay attention to is something that you can’t necessarily see but is easy enough to check. Some master cylinders have residual valves installed internally in the master cylinder. If so, these must be removed or there will be a constant drag on the rear brakes.


Do you need a proportioning valve for a disc brake conversion? 

In most instances, people are using a combination valve of some sort if the car already has front disc brakes. If a factory valve is present, it is probably best to replace the valve with a disc/disc combination valve because of the unknown. 


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Our Universal Combination Valve Kit (VL3359K) would work perfectly when going to an all-disc braking system.


If the car already has a universal combination valve, it may be able to be converted to a disc/disc. 

In both instances, what we are trying to do is remove the metering valve from the system. 

What is a metering valve? 

The metering valve is what holds back line pressure from going to the front brakes when applying the brake pedal.  Since drum brakes take slightly longer to apply, the metering valve holds off pressure on the front disc brakes long enough for the rear drum brakes to catch up, preventing a nosedive. 

In a four-wheel-disc vehicle, we want all four brakes to apply evenly, so a metering valve is not desired. 


Park Brake Cables

Should you get a new set of park brake cables? It really depends on the application. 

Some vehicles have OEM cables that can simply be converted from the attachment on the brake drums to the new brake discs. Some situations, however, will require a completely new cable and approach. 

In this case, look into a universal cable system, such as our HWC2500 or HWC2501. Something like this might just make your life a little easier.

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Legend Series Universal Park Brake Cables (HWC2500)

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Pro Driver Series Universal Park Brake Cables (HWC2501)

A Case Study: Dave’s GTO Rear Disc Brake Conversion Project 

“Dave” has a ‘66 GTO he uses as a daily driver and wanted the enhanced performance and stopping ability of disc brakes. But as the sole driver of the car, Dave was comfortable with the pedal effort the manual brakes currently required and wanted to keep that same level of brake feel.

His question centered around the fact that he had bought a master cylinder approximately five years ago in an effort to make the car safer by getting rid of the single bowl master cylinder. At that point, he was only concerned with that safety factor of the master cylinder. 

Things change, and now he is interested in converting over the last step of safer brakes and going with a disc brake conversion kit. 

Dave previously ordered one of our master cylinders, so we pulled up his past order to make sure it was the right match for his new disc brakes, and it was. 

Let’s assume for a minute though that we didn’t know anything about Dave’s master cylinder. 

How can you tell if your master is appropriately sized to operate a new (disc brake) system? 

The bore size is critical when selecting a master cylinder for use in either a power or manual apply brake system. 

The wrong size master cylinder added to a power assist set-up could actually provide for a pedal feel that is even harder than what a well working manual system would ever provide. 

Measure your master cylinder bore size to make sure it’s the right fit. With a good ruler, measuring a master cylinder bore size is actually quite easy. 

Here’s how:

After pulling the master cylinder forward on the studs, measure the inside of the bore on the back of the master cylinder. 

  • Smaller bore size = Greater line pressure in the system at a given pedal effort
  • Larger bore size = Less caliper movement = Hard brake pedal 

Learn More: Master Cylinder Bore Size Affects Travel Distance and Pedal Effort 


As always, if you have any questions or need help on this project, reach out to our Tech Team for assistance.

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