DISC Q & A
There are several causes for brake squeal and sometimes solving a squeal issue can be the result of trial and error. The most common causes are;
1. Excessive friction for the application. High performance or race pads used in a light duty application.
2. Brake pad contamination. Dirt, grit, glazing or lubricants.
3. Lack of contact between the pad and rotor.
4. Rotor surface un-even or surface rust build up
5. Brake hardware damaged, Guide pins, abutment clips, springs.
6. Some pads require the use of grease in between the shim and plate.
There are two common causes for steering wheel vibration, friction material deposits and disc thickness variation (DTV).
Some friction material technologies rely on an even layer of friction material transferred onto the disc surface. This is called a transfer layer. When this layer becomes irregular in thickness brake shudder will occur due to a grab and release effect from the pads on the disc rotor when braking. This oscillating torque from the brakes will transfer to the steering rack resulting in steering wheel vibration.
Disc thickness variation, DTV is an irregular wear issue with the disc rotor. As the name suggests, the thickness of the friction disc varies causing the pads to grab and release braking. Both symptoms result in the same effect but for different reasons.
DTV is typically caused by incorrect fitting of the brakes. The two most common fitting errors are not cleaning the hub mating faces correctly and irregular wheel nut torque, typically from the incorrect use of pneumatic impact wrenches.
Pedal pulsation is when the brake pedal oscillates up and down while applying the brakes. This is almost always the result of hydraulic line oscillation due to DTV in the disc rotor. The variation in thickness of the disc rotor causes the caliper pistons to extend and retract transferring brake fluid back and forth in the hydraulic circuit to the brake pedal.
Definitely yes! All disc rotors will have some form of anti-corrosion treatment applied before packing. Regardless of whether the disc has an “En-Shield” type painted coating or just anti-corrosive fluid, they should be cleaned. Methanol based brake cleaning products are readily available to clean the disc surfaces. The best method is to apply the cleaning product to paper towel or a cleaning cloth and wipe the disc friction surfaces and hub mounting face. When no more grease or oil products transfer to the cleaning cloth you’re good to go.
While carburettor (carby) cleaner is effective as a cleaning solution, the chemicals used in this product are intended to leave a residue.
The residue from “carby” cleaner often negatively affects the bedding in process therefore this product is NOT recommended.
Please note: spraying some aggressive cleaners directly onto new painted surfaces of the disc rotor can damage the paint finish quality. Apply to a cloth or paper towel first.
The slots in these rotors assist in the evacuation of brake dust, maintaining a clean friction surface between the pad and rotor. This maximises friction performance and eliminates pad glazing, a common cause for brake noise, poor braking performance and overheating.
Slotted rotors are highly recommended in applications where frequent braking or heavy loads are present, such as trades vehicles, 4wd’s, performance vehicles and vehicles towing heavy loads.
These applications typically produce more dust and debris than standard street vehicles and greatly benefit from the regular dust evacuation performed by the slots.
Brake pedal modulation is the controlled application and release of the brake pedal when towing heavy loads or descending steep hills. Typically, the brake pedal is applied slightly heavy than normal for a few seconds and then released to allow the brakes to recover before applying again. This lowers the temperature and stress on the brakes compared to holding the brakes on continuously and potentially inducing brake fade or loss of friction performance.