In this article, ZF Aftermarket provides important information on this common problem
Brake shudder is essentially rotational vibration of the steering wheel which can occur during braking and is usually accompanied by a booming noise.
Depending on the cause, it can be divided into thermal shudder, which occurs during deceleration from high speeds, and cold shudder, which can occur at any speed.
“Thermal shudder” is marked by a booming noise in a frequency range between 100 and 250 Hz. The intensity of the booming can vary during deceleration but does not affect braking. It is normally accompanied by vibrations in the steering wheel and a pulsation in the brake pedal.
The effects of hot shudder can usually be identified by a circular arrangement of spots on the friction surfaces of the brake disc.
This martensite formation is harder than the basic structure of the disc material and can be removed only by machining. When repairing a disc with martensitic spots, ZF Aftermarket encourages you to make sure you completely remove the hardened areas without reaching or falling short of the minimum thickness of the brake disc.
“Cold shudder” occurs during normal braking and can be identified by pulsation in the brake pedal, torque fluctuations in the steering wheel and/or vibration of axle and chassis components.
Cold shudder can occur virtually every time the brake is applied, regardless of temperature, and has a much lower frequency range (about 5 to 50 HZ) than thermal shudder. These noises can be louder or quieter depending on the speed.
The main cause of cold shudder is the thickness variation in the brake discs. Defective bearing parts and wheel imbalances can also increase the effect, as with thermal shuddering.
In most cases, brake shudder is caused by several factors, making it difficult to clearly identify the root cause. ZF Aftermarket offers the following as some general steps to follow:
• Determine whether the shudder is coming from the front or rear axle.
• Check all brake components including the brake pedal, brake booster, master cylinder, brake lines, brake hoses and wheel brakes. If replacing components, make sure to replace brake pads and brake discs, brake drums and brake shoes in complete axle sets.
• Check the wheels for balance, axial runout, radial runout and the condition of the tyre tread.
• Check the axle settings, wheel suspension, steering components and adjust/repair as necessary.
For further information on ZF’s TRW braking range, visit www.aftermarket.zf.com/au/trw