Bendix diagnoses common braking issues

Braking systems are complex and feature many moving parts; they also operate under demanding conditions such as extreme heat and cold. Throw in challenging road surfaces and dirt and debris, and its no wonder that braking faults can appear from time to time especially if maintenance is neglected.

The braking system is complex and features many moving parts; if not properly maintained, faults can appear.

Some faults are easier to identify than others; here are several of the most common.

Noise related
Given the various moving parts within the braking system, and that components such as brake pads and brake shoes make contact with rotors and brake drums with force, it’s difficult to completely eliminate noise, but noise should not be excessive or overwhelming.

Squealing brakes are often caused when friction materials (brake pads or brake shoes) contact the disc rotor/caliper or brake shoe causing vibration. The noise could be caused by poorly lubricated components including caliper hardware such as pins, slides and bushes; brake pad backing plates; brake shims and other metal to metal or metal to rubber contact paints. This noise may also indicate a scored rotor surface or that the friction material is badly worn, with metal-on-metal contact occurring.

If components including slide pins are not properly lubricated, excessive brake noise can occur.

Changes in pedal feel
Certain braking system issues can be felt by the driver at the brake pedal. A soft or spongy pedal can mean that there’s air in the brake lines or that the brake fluid is very low. Other causes could include a damaged or leaking brake booster or brake master cylinder, meaning it won’t maintain sufficient hydraulic pressure in the system.

If the brake pedal is difficult to push, this could be caused by a malfunctioning brake booster. The brake booster multiplies the force at the brake pedal to something much greater by the time the pads and shoes bite at the rotors or drums, so if not working correctly the driver will need to push on the brake pedal much harder.

A spongy brake pedal may indicate air in the brake lines, leaking or low brake fluid or a leaking brake booster.

Vibrations or pulses through the brake pedal are other symptoms of an issue. Pulsation is normally caused by Disc Thickness Variation (DTV) or warped rotors. DTV can occur if disc brake rotors haven’t been installed correctly – perhaps because of uneven lug nut torque, damaged studs or debris between the hub and rotor – and lateral rotor run-out can occur. This causes side to side movement as the rotor rotates rather than the rotors circulating through an even plane.

Warping occurs where the rotor surface becomes uneven and is often caused by excessive heat in the brakes. Through regular high-load braking situations, the rotors can become glazed from the brake pad materials rubbing off on the rotor at extreme temperatures.

Extreme temperatures changes can also cause warping, for example heavy braking followed by submersion in cold water, such as might be experienced off road when four-wheel driving.

Reduced braking performance
A noticeable reduction in braking performance should be taken very seriously and addressed immediately. When in correct working order, brakes should quickly and efficiently slow the vehicle up in a straight line with minimal effort.

A vehicle that pulls to one side under braking normally signals an imbalance within the system, and could be caused by a sticking brake caliper. The root problem may link back to poor caliper slide pin lubrication or corrosion/debris at the caliper piston(s) which causes the caliper to drag.

Excessively worn friction material on pads and shoes can lead to increased brake noise and reduced stopping power.

Needing a longer stopping distance can also be caused by worn disc brake pads or brake shoes – the thinner the friction material becomes, the less effective braking becomes.

In certain conditions and driving environments brakes can also experience a temporary reduction in performance, this is known as brake fade. Brake fade is caused by the added heat that’s generated from repeated or sustained braking, or braking under heavy loads. When the heat doesn’t effectively dissipate, the braking becomes compromised.

Drivers can minimise brake fade by ensuring the braking system is in good order; upgrading some components should also be considered if the vehicle is regularly used in situations where the brakes are worked hard. They can also adapt their driving style so that less pressure is placed on the brakes.

Pulsation and brake shudder through the brake pedal can be a symptom of Disc Thickness Variation (DTV).

Another factor than can affect performance is old brake fluid. Over time brake fluid can absorb small amounts of moisture through imperfect seals, microscopic holes in rubber hoses or even if the cap is left off the brake fluid reservoir for too long. This moisture can gradually mix with the brake fluid increasing its water content and impacting how effectively pressure applied at the brake pedal is maintained all the way to the brake calipers or drums, it can also lead to a lower boiling point for the fluid. Hot temperatures amplify the problem, as do demanding driving conditions, such as when towing.