Mastering Brake Drum Measurements

Revised July 19, 2023

The Ultimate Guide for Class 6-8 Semi Trucks

In the world of heavy duty trucks, safety and efficiency are the cornerstones of success. If you own or drive a big rig, you need a good braking system for safe and worry-free driving. The unsung hero behind your truck’s powerful braking performance is the brake drum – an essential component of your braking system.

Measuring a brake drum accurately can be difficult, especially when trying to find the right replacement drum. Fear not! In this comprehensive guide, we will unveil the secrets to measuring a brake drum like a pro. So buckle up, and let’s dive into the world of precise measurements and optimized braking power!

Brake Drum: More than a Beat

Before we dive into the measurement process, let’s understand what a brake drum is. A brake drum is a vital component of the truck’s air brake system, positioned on each wheel. When you use the brakes, the brake shoes press against the brake drum, creating friction that stops the wheel from turning.

Measurement Challenges

One problem heavy duty enthusiasts often encounter when measuring their truck’s brake drum is inaccurate measurement caused by wear and tear. Over time, brake drums can develop irregularities, affecting the accuracy of measurements.

In such cases, we recommend having a professional mechanic inspect the drum. FleetPride’s Heavy Duty Experts™ are nationwide and can accurately measure for replacement. Click here to locate the nearest service center.

Ready, Set, Measure

Now, let’s explore the step-by-step process to measure a brake drum accurately:

1. Brake Surface Diameter: The first measurement you need to take is the brake surface diameter. You can do this by determining the inner diameter of the drum, excluding the height of the drum flange. Use a measuring tape or brake drum gauge to measure across the inner surface of the drum. Be sure to measure from the inside edge to the inside edge for most accurate reading.
2. Overall Depth: Next you will want to measure the overall depth of the brake drum. You take this measurement from the top of the brake drum to the bottom of the center bore. Measure the drum from the highest point to the lowest part of the center using a measuring tape.
3. Brake Surface Flat: Ensuring the flatness of the brake surface is crucial for proper brake performance. To measure this, utilize a straightedge or a flatness gauge. Position it diagonally across the brake surface and measure the gap between the straightedge and surface. Ideally, the gap should be minimal for optimal braking efficiency.
4. Bolt Circle Diameter: is the diameter of the imaginary circle drawn through the center of the bolt holes. To measure the bolt circle diameter, use a measuring tape or a bolt circle template. Simply measure the distance from the center of one bolt hole to the center of the opposite bolt hole.
5. Pilot Diameter: The pilot diameter is the center hole in the brake drum, where it mounts onto the wheel hub. Use a caliper or a measuring tape to determine the diameter of the hole accurately.
6. Bolt Holes: Count the number and size of bolt holes on the brake drum. Additionally, measure the diameter of these bolt holes using a caliper. This information is crucial to ensure a perfect fit for the replacement drum.

And just in case you are a visual learner, here is a diagram:

FleetPride. Your Roadmap to Confident Replacement.

Being well-versed in measuring a brake drum is vital for maintaining your rig’s safety and performance. By accurately measuring these key factors mentioned above, you can ensure a seamless replacement process.

If you have any questions or worries, ask FleetPride’s reliable experts in the heavy duty aftermarket industry for help.

Now you can use your knowledge to measure your brake drum correctly. You can confidently purchase a new drum from FleetPride.com, the biggest distributor of truck and trailer parts in the country. Upgrade your braking system today and experience enhanced safety and efficiency on the road.

* The forgoing is provided for informational purposes only. Please consult your local FleetPride Heavy Duty Experts to verify the suitability of a part for the intended application.