Today’s commercial vehicle braking systems are more powerful, effective, and safe than ever, and proper upkeep is critical for helping them do the best job they can. And while expert, trained technicians and the right repair facilities are irreplaceable parts of any truck or fleet maintenance blueprint, there are several simple wheel-end steps vehicle owners can take regularly to help maximize time on the road and minimize downtime.

Before You Hit the Road

Never forget that pre-trip visual inspections are an absolute must. A few extra minutes and a keen eye can prevent big air brake problems down the road. During a walk-around of the tractor and trailer, look for loose or hanging hoses, slack adjusters, and air chambers. (Pay extra attention to the chamber pushrods to make sure they’re not broken or bent.)

Basic checks of air disc and drum brake conditions can be done without removing the wheel, and should be done once or twice a week. Check air disc brake rotors for cracks, and check guide pin boots and tappet boots for cracks or tears that could allow moisture inside the caliper. On drum brakes without dust shields, inspect for cracked friction and lining wear.

What to Know about Slacks

Brake performance is a key indicator of component condition. Dragging drum brakes, for example, can point to a slack adjuster that’s over-adjusting – which means it’s “chasing the drum.” (Drums expand during normal use, then contract again as they cool. If a slack adjuster overcompensates during the expansion, the brake will drag as the friction makes contact during the drum contraction.)

Signs of dragging brakes include leopard-spotted patterns on drums, or grooving on air disc brake rotors.

If a drum brake is dragging or found to be overstroking (out of adjustment), and is equipped with automatic slack adjusters, it’s important to avoid the temptation to do a manual readjustment. Automatic slack adjusters aren’t maintenance-free, but they are designed not to need manual tweaking. There are several factors that can affect their operation and cause a brake to overstroke, but none of these will be fixed by a manual readjustment.

Mind Your Linings

Not surprisingly, friction selection in the aftermarket and upkeep also have a huge effect on stopping power and brake longevity, so brake linings should be inspected regularly and thoroughly.

Watch for cracks or missing pieces in both disc and drum friction, and make sure they meet thickness standards. Be alert to uneven friction wear, particularly on drum brakes, where it can indicate a deformation in the brake shoe, which can decrease performance and shorten friction life.

When it’s time to reline, choosing the proper replacement friction is crucial. If the vehicle requires Reduced Stopping Distance (RSD) brakes, verify that the friction is certified for RSD compliance: Not all replacement friction marketed as acceptable under RSD will actually perform to the standard, so we recommend asking suppliers for evidence of compliance. When in doubt, the most effective way to meet the stopping distance requirements that were in effect at the time of manufacture is to replace the original friction with like-for-like OE friction.

There’s no substitute for the right talent and time in the garage, and every vehicle in your fleet should be part of a proactive and consistent preventive maintenance program, but good wheel-end check-up habits and knowing what to look for can help prevent big trouble down the road.

Bendix Blog

Technical and industry insight from OUR experts.

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