CAR CLINIC

Why your car vibrates when you brake

In Summary

•Under normal circumstances   when a vehicle is on the road, brakes must be applied.

•The friction between the rotating disk and the brake pads produces heat that eventually heats the disk. 

Car disk.
Car disk.
Image: BOOSTED AUTO

You are driving on a smooth highway then suddenly the traffic slows down.

The moment you step on the brake pedal to slow down your vehicle, a vibration is felt on the steering wheel. It becomes so severe that you have to let off some force from the brake pedal to ease the discomfort that is brought about by this issue or else the entire car will get into a vibration fiasco hence increasing the braking distance.

The vibration starts from the brake pedal harmonically kicking back your foot in quick successions and increasing to other parts of the car according to how much you increase the braking force on the brake pedal. This vibration is known as brake judder.

WHAT CAUSES BRAKE JUDDER

Brake judder is associated with warped discs/rotors.   To avoid brake judder, we need to understand what causes the disks to warp and how to avoid it. In many cases, a larger percentage of disk warping is caused by human error unknowingly.

Under normal circumstances   when a vehicle is on the road, brakes must be applied. The friction between the rotating disk and the brake pads produces heat that eventually heats the disk. Sometimes when this heat is too much it makes the disk glow red hot.  If the vehicle comes into contact with a pool of water on the road, the water gets to the disk and forcibly cools it down.

Cooling the disk suddenly causes it to bend because of uneven cooling. Due to this uneven cooling, the disk will naturally bend (warp) and will cause the vehicle to judder when the brake is applied. It is not easy to say one can cool the disk evenly but in the first place if you are driving in a zone with too much water trapped on the road why would you want to heat your brakes too much so that you cook them evenly.

If you must heat your brakes due to your bad driving habits then when you come to a pool of water on the road kindly avoid it by all available means.

Another cause of disk warp is due to hard braking.  The chances of a brake disk becoming malleable (soft) at high temperatures are very high. When you hit your brakes so hard, the impact by the brake pistons on the brake pads is directly going to hit the soft disk with a lot of force causing it to slightly deform in what is technically known as Disk Thickness Variation (DTC). The aftermath of this deformed disk will be brake judder the next time you are breaking.

Most brake judder is caused by this hard braking without owners realising their mistake.  The thickness of the disk both on the inside and outside is supposed to be the same. Any small variance in its thickness will cause the brake pads not to move along its surface smoothly.  The brake pads will always move out at the thicker part and move inward at the thinner part. The speed at which this is happening will depend on the force applied on the brake and the speed of the car the annoyance and discomfort   brought by these actions are not bearable.

If the thickness of the disk is still within tolerance instead of replacing it with a new one, skimming is the best option, but if the driver continues with hard braking the brakes won't last for long without brake judder.

A special type of grease known as copper grease must be applied between the brake pads and the caliper whenever new brake pads are fitted.  The main purpose of this is to ensure that conduction of heat is taking place from       the disk to the caliper through the pads. This way at least the disk cools out faster. The second main purpose of this grease is to ensure that the pads are freely moving in and out of the caliper upon brake application. Otherwise, if the grease is not applied, chances of pads getting stuck on the rotating disk are so high and this can lead to too much friction which means you much heat generation which may lead to brake fade N\B always use genuine brake pads on your car. Non-genuine brake pads usually lead to too much heat generation due to bad quality materials that may lead to brake issues

The writer is the owner of Boosted Auto Repair Shop