Traditionally, almost all long-haul trucks came equipped with drum brakes. While economical, drum brakes tend to be harder to work on. In addition, they don't perform as well in certain high-use situations, such as braking while coming down a steep hill. As a result, more and more operators have opted to switch over to disc brake systems.
Disc brakes offer many benefits, both in terms of performance and ease of servicing. Yet because many operators don't know as much about disc brakes, they fail to recognize common problems. This article seeks to improve your knowledge of disc brake wear by discussing three commonly experienced issues.
1. Asymmetrical Wear
The disc in a disc brake system attaches directly to the wheel. The inside of the disc consists of a recessed mounting face. A series of holes allows the disc to be bolted to the wheel's hub. In order to promote optimal stability, all of these bolts must be tightened to exactly the same degree.
Yet tightness isn't the only important factor. The mounting face must also sit perfectly flush against the wheel hub. If it doesn't, the problem known as wheel hub runout occurs. The result of runout involves a disc that remains at an angle relative to the caliper and brake pad. As a result, certain portions of the disc will receive an excessive amount of friction, leading to asymmetrical wear.
In addition, hub runout usually causes the brake pedal to jump and shudder when depressed. These vibrations may also travel the column to the steering wheel. Asymmetrical wear reduces braking power. Over time, such wear will also cause portions of the disc to reach their wear threshold prematurely, necessitating replacement.
2. Disc Brake Scoring
The brake pads close around the surface of the disc brake in order to generate stopping power. This contact also creates friction that wears away the brake pad. In some cases, however, the friction and heat of slowed rotation may also cause damage to the disc surface in the form of scoring.
Scoring can create a large range of wear patterns. The principle feature of scoring are scraped, gouged, or otherwise roughened patches. If minor enough, a technician can often remove scoring by sanding and polishing the disc surface. More severe instances may require that the disc be replaced altogether.
Scoring can give rise to a large range of symptoms, from shuddering, to strange noises, to decreased braking power. The most common cause of scoring involves incorrectly matched friction pad and disc surfaces. For instance, pairing an especially hard friction pad with a softer disc metal will increase the likelihood of scoring.
3. Mounting Face Cracks
As discussed above, the disc mounts to the wheel hub using a series of bolts. These pass through holes - known as bores - in the disc's mounting face. In some cases, cracks may develop around the bores because of the high levels of stress placed on the mounting bolts.
A cracked mounting face often suffers from excessive movement when applying your brakes. As a result, your brakes may seem to shudder and shake. Ultimately, the mounting face may become deformed because of these stresses. Likewise, the cracks may continue to grow until the disc fails outright.
Mounting face cracks commonly stem from improper tightening - and specifically from bolts that have been over-torqued. Alternately, the installer may have failed to tighten the bolts in the appropriate order. Unfortunately, replacement remains the only remedy for a disc brake with a cracked mounting face.
To ensure optimal safety and to minimize repair costs, you should always hire a professional to service your disc brakes. For more information, contact truck experts at Odessa Spring, Brake & Axle, Inc.