Letter Of The Week–Brakes That Squeak

For whatever reason, I’m obsessed with the brakes on our dirt bikes. One question that no one seems to be asking, and no one I ask has given me a real answer to, is this: Why is it that the rear brake of an off road motorcycle howls like an injured animal? Not everybody’s does it, and I used to think it was just my Gas Gas, until I bought a KTM. Is there a good, scientific reason for the squeaky brakes? Always looking for long lasting brakes that work well and have good feel. Which begs the question. Is there a pad material that solves the screeching sound of the rear brake?

Mike Sheetz

AP-Brakes-12

Mike,

We have worked with some experts in the braking field on both the development side and in general testing and there are a number of factors that cause the squeaking, We even turned to motorcycle safety testing expert Chris Real of DPS Technical (www.dpstechnical.com) to get an outside view and everyone came up with the same answers. 

The first is wear or worn components, especially the brake pins the pads slide on. As soon as these develop any wear they do not allow the pad to move as it should and in turn get out of line and it causes vibration which you hear as the squeak. 

When the pins the caliper slides on dry up the same can happen but usually this is indicated by uneven pad wear between the two pads.

Some non-OEM pads also have more ceramic or metal in them, these are noisy as well. They wear longer and may even have better bite at certain temperatures but the friction on the rotor can cause the squeak too, as well as additional rotor wear. Pads that get a fine dust on them can squeak even when they are not that hot. Or even pads that are run in very muddy conditions then run again later after they dry as the now-dust gets between the pad and rotor.

Brake noise is common from a wear pattern on the inside of the pad making contact with the outer edge of the rotor. This is often a sizing issue with non-OEM pads or rotors.

Any water in the brake fluid (or old overheated brake fluid) will expand and cause the brakes to drag. Dragging brakes cause heat, heat aggravates the squeak.

Different rotors with different hole patterns and shapes can have different sounds and vibrations. Floating rotors are also very prone to this and that is why they are uncommon on the rear of a motorcycle.

The last thing may be the spring retainer getting cocked and rubbing on the rotor.

Solution is to change the fluid, use OEM pads (because they are usually tested to not become squeaky under normal use, but that does not include brake dragging!) or trying different ones to find what works. Different materials really do have different feel and performance (as you have read in the AP Brake pad test: http://dirtbiketest.com/product-tests/ap-brake-pads/  if you take the time to test them. But most of all keep the pin in good condition.

JIMMY

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