How To Measure Brake Drums: A Complete Guide

Little did you know, understanding why and how to measure brake drums is vastly crucial.

This is because inspections like that can not only help make sure that the cars’ drum brakes are functioning properly, but they can also avoid unexpectant breakdowns.

Follow through with our in-depth procedure, and we are sure you will be just as fine being on it yourself! Read on for more.

What Are The Standard Drum Sizes?

how to measure brake drums
Standard Drum Sizes

The steering axle brake lining or pad must be normally thicker than 1/8 inch (3.2 mm). And that is only counted as for air disc brakes.

How about a drum, hydraulic disc, and electric brakes? Then the answer should be at least 1/16 inch (1.6 mm).

Many may not mind such minor details of their automobile, but let us tell you something: Brake drum sizes do matter!

There is a limit size for the mechanism intended to retain the replaced friction pads. The more your brake drums are in their precise, appropriate size, the better braking performance you can gain.

Too-large drums prevent the brake drum shoes from applying sufficient pressure to the drum for effective braking.

Too tiny drums can also cause you a lot of trouble installing them. Even if the set-up process is successful, you will run into some braking problems one way or another.

How To Measure Brake Drums

drum brake shoe thickness chart
The Ways Measure Brake Drums

Step 1

How to measure a brake drum? Let first commence the process by removing the whole drum brake assembly from the wheel.

By the time you do so, don’t forget to clean out any grit or dirt that has developed on the brake shoes and drums as well.

Then, depress the retention clip using a little screwdriver and a small-sized spoon to take off the star adjuster from the brake shoes.

You may also need to prepare a wrench or other tool occasionally just to be in case so you can locate the bolt retaining the drum.

Now, to remove the drum, turn the bolt in a counterclockwise direction and pull it off. Certain drums might need to get removed with the aid of a drum puller.

Step 2

It will be important to look over the rotor and record the largest possible size or diameter if your car features a drum braking system.

In addition to drums in the system, sensors are also another essential component used by the majority of manufacturers.

Check up on the brake drum thickness chart that lists the brake drum specification guide and maximum diameter for disc-brake assemblies employed in cars from the identical manufacturer, or have a look at a table that contains information on this sensor or its replacement.

Do whichever way you wish to, as long as you do not neglect this step, and you’ll be on your way to getting the task completed!

Now, it’s time to keep track of any permitted run-out (to gauge excessive wear) and carefully compare measurements to other automobile makes and models.

Step 3

You’re halfway there, with only a few steps to go!

This measuring procedure of your drum’s internal diameter will first need you to position it on a flat surface with the inside diameter pointing up.

Remember to check the condition of the drum’s center for any indications of brake drum cracks or grooves.

After that, make a visual inspection on the region where the rim encounters inside.

Doing so will help you make sure there are no chips or flakes that might fly off and possibly damage micrometer anvils in the system.

Step 4

The next vital tool you must have is the micrometer, with a length of no less than 15 inches. It will be fine if your drum is shorter than that.

For example, setting it to the 10-inch mark for a drum with a length of 10.5 inches shall be merely a picnic, but not vice versa.

Next, create another 10-inch mark and split the other 0.5 inches into four equal portions.

Step 5

Make the locking screws along the shaft on one of the micrometer arms loosen. The loosening will assist you in sliding it down the shaft at 10 inches.

A genuine drum size shall be a great help to get the most accurate measurement. Start by positioning one side of the micrometer at the 10-inch mark on your vehicle’s braking system.

Then meter one side to 10 and add four further inches from there, and that’s how you achieve your brake drum measurement of 10.5 drums!

Step 6

Now, it will be the stage of a device used to assess shoe thickness, so-called a depth gauge or also known as a shoe gauge.

All you need to do is merely insert this special tool’s tip into a hole or aperture in the shoe, and there you get a precise reading.

As you measure a riveted shoe, bear in mind to place your depth gauge below or above the rivet to get an exact reading.

You will know whether your shoe has used its time when the 2/32 inch you’ve been eyeballed decreases or suddenly becomes any lesser than it should. Then, let’s get a new pair of shoes.

When Should You Replace Your Drum Brakes?

brake drum measurement
Replace Drum Brakes

Brake shoes and drums thin out as they become older. They eventually deteriorate and need upkeep. Moreover, wheel cylinders degrade and begin to leak.

Each of these flaws has the potential to result in the following indications, naming the shaking or pulling-to-one-side of your automobile’s back, a soft sensation featured in the brake pedal, the car being sloppy, the brakes squeaking or grinding when engaged.

Have your rear drum brakes serviced if you detect any of these symptoms. Normally, brake drums are simple to repair and are designed to serve you from 100,000 to 150,000 miles.

The components inside the drum, however, require more regular inspection and maintenance.


What Tool Is Used To Measure Drum Brakes?

A little screwdriver and a small-sized spoon, a wrench, a drum puller, a micrometer with a length of no less than 15 inches, and a shoe gauge are basically all you need to prepare in your kit to measure brake drums the appropriate way.

Feel free to adjust some of them if you wish to, but make sure you do not risk putting your procedure into any damage.

Which Brake Measures Are Reliable?

For the best performance, we advise you to maintain the thickness of your brake pads anywhere above 6.4mm.

Be mindful of the minimal brake pad thickness, which is exactly 3.2mm (even the close one like 3mm can cause problems), since if your own brake pads fall less than this, you will eventually need to replace them.

Do Drum Dimensions Matter?

Yes, drum dimensions are just as important as how to measure drum brakes. As aforementioned, the device used to hold the new friction pads in place has a size restriction.

The more your brake drums are exactly the right size, the greater the braking performance you will get.

What Is The Maximum Drum Diameter?

The greatest permitted wear the drum may safely withstand before the metal becomes too thin is the discard semi truck brake drum wear limit of 0.090 inches.


Average drum brakes should last you at least 200,000 miles due to their construction, but they will eventually wear out.

That is why it will never go redundant to keep up with its status and pack yourself with decent knowledge on how to measure brake drums.

Hopefully, our article can be of great help to you. See you then!

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