Is your slack a drag on your bottom line?

Brake drag. Of course, you know what it is, but are you seeing it on your vehicles? From talking to fleets and visiting their shops, I’ve found that very often they don’t know they have brake drag. They think the amount of friction and drum wear they see is normal because they’ve always had that accelerated wear during the life of a brake shoe. Plus, it’s often undetectable to the driver. Although the wear they’re seeing is actually premature, fleets continue to change out shoes and drums on their typical schedule.

For starters, it’s important to recognize the signs of brake drag:

  • The tires do not rotate freely (with the vehicle jacked up)
  • You must regularly back off your slack during typical maintenance
  • The drum is difficult to remove
  • Inability to see any running clearance between friction and drum

If you experience any of these conditions regularly, you may have brake drag. These conditions call for further inspection of your wheel end to address the accelerated wear you may be seeing, along with the extra fuel your vehicle is likely consuming. Start by referencing the slack manufacturer’s instruction manual for troubleshooting information, but one reason you may be seeing brake drag: the slack adjuster you’re spec’ing.

What causes brake drag?

Some slacks adjust too quickly when the drum heats up and expands during braking. When the drum cools down and contracts, the running clearance (or gap between the drum and shoe) is greatly reduced, or even eliminated. With no running clearance, the brake continues to drag, only correcting itself over a long period of time with normal brake applications that wear the friction down, away from the drum surface. This brake drag condition becomes somewhat repetitious in nature, and therefore over the long-term, and thousands of miles, it can have a big impact on your vehicle’s total cost of ownership (TCO).

The impact on lining & drum life

If you do have brake drag, it’s certainly not business as usual. Anytime you have brake drag, the brake should be serviced to determine the root cause. Brake drag can shorten lining and drum life. When we compared the performance of our Versajust® Slack Adjuster to a slack that had exhibited drag in a Bendix fleet test, we found that Versajust extended lining life by up to 16% and drum life by up to 30%. With brake drag, you’re also looking at additional (and unnecessary) downtime, maintenance costs to perform brake jobs, and the cost of replacement parts.

Nobody talks about increased fuel consumption

After initial testing showed that Versajust extended lining and drum life, we wanted to further examine another impact of brake drag…fuel consumption. When the brake drags, more fuel is consumed as the engine and throttle must overcome a certain level of deceleration in order to maintain a certain speed.

To quantify fuel consumption, we conducted third party testing at a test track comparing a vehicle with dragging brakes versus a vehicle with no brake drag. The test results showed that the truck with drag showed significantly higher fuel consumption than the truck with no brake drag. There was a fuel consumption penalty of 1.5% for the dragging brake. Think about the cumulative effect of this extra fuel consumption multiplied by the number of trucks in your fleet and the miles they travel.

Drum life, lining life, fuel efficiency—to say nothing of safety and brake performance—mean there is a lot riding on the slack adjuster you select. So, choose a slack adjuster that doesn’t penalize your bottom line. Reduce the risk of brake drag, optimize brake wear—and improve fuel efficiency—choose Bendix® Versajust® Slack Adjusters.

For more information on fuel savings and brake drag, contact Mark Holley at or 859-962-9897.

Bendix Blog

Technical and industry insight from OUR experts.

Why the REPAIR Act Matters for Trucking

Congress is considering legislation to ensure that the right to repair vehicles is available to anyone qualified to repair them. For trucking, this right is essential. Why? Let's find out.

Read More

FMCSA’s “Large Truck and Bus Crash Facts” 2021: Crashes Are Up. So, What Are We Going to Do About It?

More vehicles, more traffic, more potential opportunities for collisions? Let's dive into the data.

Read More

Since We've Discussed the Donut Hole, Let's Talk About the Donut

The why, what, and how of the AEB (Automatic Emergency Braking) Notice of proposed rulemaking (NPRM) – part 1.

Read More