What causes juddering brakes?

Identifying the culprits behind brake judder is essential. Driver habits play a significant role, particularly in automatic vehicles where brakes are often applied only once the vehicle is stationary.

However, this practice can be problematic when stopping from high speeds, as it leaves the brakes exceedingly hot. Consequently, when brake pads are pressed against these overheated discs, the likelihood of warping a common cause of vibrating brakes, increases.

Most modern automatics will have an auto function anyway which helps to avoid this. 

Manuel’s are not exempt from this same issue, but that means sticking it in neutral and applying the handbrake. Yes, it does sound like an old driving lesson, but your brakes will be thankful for it. 

– Hot and Cold, warping can also occur when the brakes are subjected to extreme and sudden temperature changes. Temperature extremes can lead to brake disc warping, such as when driving through water with heated brakes, exacerbating brake vibration.

– Below minimum thickness, Once a disc has worn below or close to its minimum thickness, this can reduce the compressive strength as it wears.

This reduced thickness also impacts how heat is moderated over the surface of the disc. i.e. a thinner disc is likely to heat up quicker, making them more susceptible to warping and even cracking under high-speed braking.

– Lateral run out, When the disc isn’t running true against the hub, it will create an in balance within a full 360 rotation. This can be caused by several reasons such as dirt and debris sitting behind the brake disc. Loose or worn suspension components, excessively worn wheel bearings or even and over torqued brake disc retaining bolt.

Aftermarket alloy wheels can be designed with different hub details, be sure to check that the alloy wheel face matches up to the brake disc detail. Some manufacturers can supply wheel spacers to alleviate this problem. 

– High spots, When a car is parked up idle for long periods, this can cause corrosion between the disc and the pad. You may have noticed this when you set off in your car after leaving it for a long time, there is a mild humming or juddering when braking. Most of the time this can clean off after a few miles.

The worse this corrosion is, the longer it can take for this high spot to disappear and increases the risk of damaging the brake pads. 

– Overheating, Excessive amounts of heat created under braking can lead to hot spots and eventually distort the disc itself.

Look out for localised blue heat spots, if these appear just replace the whole set of pads and discs. 

– Disc thickness variation (DTV), If there is a slight variation in the thickness around the disc this can cause brake juddering.

For those keen on delving deeper into maintaining smooth and reliable brakes, and avoiding the disconcerting sensation of juddering brakes, resources such as Brake & Front End offer extensive guidance.