Brake Juddering Mechanical Services Blogs Aarya Auto


Why does my car judder when I brake?

Have you ever experienced Brake pedal pulsations or Brake juddering on your vehicle? It is quite obvious that as a driver or as a user of any new generation vehicle available in the current market you experience the problem of brake pedal pulsation or brake juddering, at least once. Unfortunately, this problem has been widely misunderstood among top automotive aftersales professionals for decades.

When anyone reports such an issue of brake pedal pulsation or brake juddering, the first reaction that comes from the service team is that it is due to wrapped or distorted brake discs (rotors). To date, rotor refacing is widely done as the remedial measure for the problem worldwide. Let us dive a little deeper into the problem so that we can understand it better.

Most of the mechanics and service advisors believe that the root cause of brake juddering is due to the distortion or warpage which develops on the brake and are rarely discovered.
They generally will recommend you to change the brake pads and do disc skimming to correct the surface of the disc without any second thought. But in reality, if you observe and measure, it is not the warpage but the Brake Disc Thickness Variation (BDTV) is the root cause of the problem. BDTV is a variation in thickness of the disc rotor braking surfaces as it rotates on the axle. 

Now let us check how BDTV occurs in some vehicles. The hydraulic braking pressure from the brake master cylinder behind the caliper pistons forces the brake pad to maintain a consistent load on the rotor surface.  But when there is frictional contact happening between the rotor and brake pads, it generates a lot of heat on the brake disc and pads. As most of the brake disc which is made 
up of cast iron and brake pads which could be made up of ceramic or any other frictional materials the heat distribution on both will be uneven surfaces which allow some mutual material transfer between the brake pads and brake disc. Such material transfer is distributed unevenly on brake pads and brake disc surfaces to create high or low spots. Those high spots on the rotors become very hot comparing with the rest of the brake disc

area and a property change happens, creating wearing-out pattern that will change from the rest of the rotor surface area.  Usually, with the help of the naked eye we cannot identify such spots on the disc surface. When the thickness of the disc rotor varies by as little as 15 to 20 microns, the brake pads oscillate back and forth causing a pulsation in the hydraulic circuit back to the brake pedal. This brake pad oscillation also causes a variation in brake torque as the brake pads grab and release over the higher portion of the rotor thickness. This is typically noticed in the steering wheel as the brake torque from the left and right axles is different and out of sequence. 

Now let us look at the solutions to the problem. If you reface the rotor disc it only evens out the surface but the high spot are still there with the changed texture and altered properties. Soon after driving a few hundred kilometers, the BDTV rebuilds again and you will have the same complaints. This is why workshops all around the globe receive these repeated brake judder related complaints.  The solution to this is the replacement of the brake disc along with brake pads once brake juddering is observed. This approach of replacing the brake disc along with the brake pads will help in rectifying the brake juddering problem and you don’t have to worry about it on occurring repeatedly.  

If you still face the same issue or have any additional queries regarding your car, contact us at 054 996 8446 (Abu Dhabi) & 054 996 8419 (Dubai). You can also visit our website to check out our car mechanical services that we provide.