How to measure drum brakes? Step by Step Easy Guide

How to measure drum brakes? Mane vehicle owners and trainees in repairing vehicles frequently ask this question because it needs a step-by-step operation. So In this article, we will guide you through the process of measuring the drum brakes of your car.

Every vehicle is not the same in appearance and system. But usually, the procedure of this is the same in almost every vehicle which has drum brakes.

What is a drum brake and how does it work?

Drum Brake system
Drum Brake system

When talk about the “How to measure drum brakes”, Drums hold the brake shoes used to stop the car. Hydraulically, the bores of the wheel cylinders expand when the driver tells them to. This pushes the shoes into the drum’s inner diameter. When you compare brake shoes to cast metal drums, the brake shoe material is softer and wears away faster than the metal drum material.

Why does measuring is needed?

There is a point when drums can’t be used anymore. It happens mainly when using the drums for a long time. There is more weight on the drum brakes because of this, which means that if the drum is too big or too thin, it will make the brakes less effective at stopping. This could also be a problem if the drum breaks down.

If a brake drum is worn down to the point that it can no longer hold the same amount of braking force, it will need to be replaced. In order for this number to be cast on the drum’s outside, it must be at least 422.1 millimeters or sixteen points six and two inches long.

Most trailers in the United States use a standard American brake or driving axle drum. The diameter of a new drum is 16 and a half inches or 419 millimeters.

So next let’s discuss the actual procedure of “how to measure drum brakes” step by step for your clarification.

Remove the drum from its place on the wheel.

If you need to remove the drum from its place on the wheel, use a drum puller. You can use a drum brake spoon and a small screwdriver to depress the star adjuster retention clip.

This will allow you to remove the shoes after they have been adjusted (if applicable to the specific drum braking system). Also, screws can be used to keep the drums from moving around on the hub face. First, remove the screws from the drums.

Find the stamped maximum diameter.

If you look at the outside surface of the rotor, you can see the maximum diameter that was stamped into the cast. If the machine-to and discard measurements on each drum can’t be read because of rust and corrosion, or if the measurements aren’t relevant to the drum, a chart for the drum and rotor discard specifications will be needed for the drum and rotor.

It’s important to find the year, make, and model of the car on the chart because each car is different. This will show you the important measurements for the car. When you look at the table, figure out the exact drum size of the car, how much run-out you can have, the machine-to specification, and the discard specification for the car in question.

Make sure that the drum inside diameter is facing up

It’s important to make sure that the drum inside diameter is facing up. To do this, place the drum face down on a level surface. Before you do anything else, check to see if the drum’s internal inner diameter and the hub’s mating surface have any visible surface cracks before you go any further.

You should look for any marks on the inside diameter. If these places are damaged, the anvils on the micrometer’s extendable arms will need to be moved back to where they belong.

Set the micrometer correctly.      

Turn the lock screw on the micrometer’s shaft on one of the arms to the left to loosen it. In order to measure the diameter of the drum, it is best to use the drum’s true diameter. Make sure the micrometer is set to the 10-inch mark if your car’s drum is 10.5 inches wide.

With the 10-inch arm, add four more of the 0.125-inch lines etched on the shaft to make the drum 10.5 inches long. This is the first figure.

Putting the anvils of the micrometer into the drum.

Putting the anvils of the micrometer into the drum, moving the micrometer back and forth along the drum’s diameter, and getting what you want will be done. It’s important to keep an eye on the drum’s dial to see if there are signs of irregular wear, such as run-out (out-of-roundness).

All of the readings should be compared after a lot of them have been taken. It is important to add this measurement to the drum’s diameter of 10.5 inches in order to figure out if it should be machined or thrown away and bought a new one.

A depth gauge should be used.

When discuss about the How to measure drum brakes, depth gage is more important. A depth gauge should be used to find out how thick the shoes are. The proper way to use a gauge when working with riveted shoes is to put its tip into the hole on the shoes’ face. People can only measure shoes that are attached to their shoes’ backplates around the edges of where they connect to their shoes’ backplates.

For each measurement, try to keep the shoe at its smallest height so that you can get the best number. It’s best to choose a new shoe if there is a big difference in the length of the same shoe. To change the shoes as soon as possible, you should measure your foot and see if it is less than 2/32 of an inch.

So now you know how to measure the drum brakes. But we know there are still some questions that you have relating to this. So we’ve embedded some YouTube videos also for you to get a better understanding of the procedure.

FAQs about How to measure drum brakes,

How do you measure drum brakes on a truck?

How to measure drum brake shoe size?

If you have more questions or suggestions on the content, do not forget to leave a comment below. We will be very happy to assist you further.

We hope you’ve got the answer that you’ve needed for the question, “How to measure drum brakes?” reading our explanation. If you have more questions just leave a comment below, and we are really straightforward to help you further. And if you need to review about brand new cars just check below page. Thank you.

Scroll to Top