What is brake judder?
Brake judder is the vibration felt through the steering wheel and suspension when the brakes are applied at certain speeds and pressures. It can vary from a barely noticeable vibration to a violent judder – experienced through either the brake pedal or steering wheel.
Causes and Solutions
Cause 1: Hub and/or rotor run-out
Brake judder can be caused by a badly fitted brake rotor pulling out of alignment with the hub or caliper. To help you identify if this is the case, here are some symptoms and solutions:
Check for rust or dirt on the wheel hub surface
Rust or dirt causes poor contact between the rotor and hub.
Dismantle the rotor and clean both surfaces to remove rust and other pollutants.
Check whether the hub contact surface has been distorted by excessive tightening torque
Using overly severe tightening torque on the positioning screw leads to vibrations throughout brake application.
Replace the rotors, avoiding excessive tightening torque.
Check for distortion of the hub itself
Although rare, it’s possible for hubs to warp. Bolting a rotor to a warped hub will always result in brake vibration. The same will happen if any rust from the hub surface is not removed before fitting the rotor.
After fitting a rotor, always check for rotor run-out using a dial gauge. If the run-out is out of tolerance, re-fit the rotor in an alternative position until the run-out is within tolerance. If run-out still remains out of tolerance, hub maintenance is required.
Check whether the alloy wheels have been fitted correctly
A common cause of rotor run-out in recent years is the incorrect fitment of one-size-fits-all alloy wheels. As the same wheel is used for multiple hub types and sizes, installers are using location spacers on the wheel spigots. If the spacer is lost or damaged, the wheel cannot be correctly centered.
Place the run-out gauge on the back of the rotor while fitting the wheel, and measure the run-out. The gauge will only show run-out once the wheel is fitted and tightened, and it may be necessary to change the wheel.
cause 2: severe rotor overheating & distortion
Any severe temperature increase can cause the rotor metal to distort in different areas of the rotor. These ‘hot spots’ cause intermittent contact between the pad and rotor, which results in judder. To help you identify if this is the case, here are some symptoms and solutions:
Check for any signs of brake abuse
Brake abuse is the most common reason for overheating. Rotors are designed to cool rapidly between brake applications. However, when the brakes are applied intensely in quick succession – e.g. during alpine driving – the rotors don’t get enough time to dissipate the heat.
Blue spots on the rotor surface are a good indication of overheating. Rotors that show blue spots and/or a darker color in some areas cannot recover and should ALWAYS be replaced, together with the brake pads.
Check the quality of the brake pads
Poor quality brake pads can overheat very easily, especially during heavy braking. The excessive heat from the pads can cause the rotors to overheat, resulting in rotor warping.
Again, look for blue spots on the rotor surface. When you can't find any, inform the driver of the risks of poor quality pads. ALWAYS replace the brake pads and rotors when you see blue spots on the rotor.
Cause 3: disc thickness variation (dtv)
DTV is the variation in thickness around the rotor surface. For effective braking, the rotor should have the same thickness throughout. If there is an uneven friction surface, the brake pad loses and regains contact with the rotor as it turns, causing brake judder. To help you identify if this is the case, here are some symptoms and solutions:
Check with the driver to see if the brakes have been properly bedded-in
To get the best performance from your brakes, it’s essential to follow the bedding-in procedure. By applying only moderate pressure on the brake pedal during the first few applications, an even layer of friction material is transferred from the pads to the rotor. Mating the surfaces this way improves safety and prevents DTV-related judder.
Prevention is better than a cure. Each time you fit new brake pads or have them fitted, avoid hard braking for the first 125 miles. When poor bedding-in has resulted in slight DTV, it may be sufficient to bed-in the brakes once again. If this does not re-align the rotor surfaces, the only solution is to replace both the brake pads and rotors.
Check for caliper seizure
A seized caliper piston or a seized caliper sliding pin leads to uneven forces being applied to each side of the brake rotor, creating uneven wear – or DTV.
This problem is usually caused by corrosion or dirt. Therefore, run the proper maintenance of the seized caliper to prevent the problem from recurring and replace both the brake pads and rotors.
Check for dirt or corrosion on the rotor surface
During braking, some of the brake pad’s friction material transfers to the rotor. But with poorer quality brake pads, the deposits of friction material can stick to the rotor unevenly, changing the rotor’s thickness and parallelism.
If there’s only minimal DTV, it may be sufficient to remove the deposits using a brush or sandpaper and road test the brakes. If this has not realigned the surfaces, the only solution is to replace the brake pads and rotors.
Check for pad imprints on the rotors
Holding the brake pedal depressed when the brakes are overheated may imprint or weld pad material on to the rotors. The DTV will often be visible as the outline of a brake pad on the rotor surface.
It should normally be sufficient to remove the pad imprint using a brush or sandpaper.
The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.
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