S2 xr6 brake questions

[Day-mow]

Since I fitted slottered rotors to my car I've herd a noise that resembles that of a flat spot. But my tires are fine. And when Rollin slowly and I softly apply the brakes sometimes it feels like my abs is kicking in. Have I stuffed up? I have RDA slottered rotors and bendix regular pads.
Any feed back would be good the car is going to a mechanic soon for it's 150k service but it'd b nice to know if it's something normal or such.

Also brakeing feels fine from speed no shudder or anything

thanks

[AU3XSR]

Originally Posted by Day-mow

Since I fitted slottered rotors to my car I've herd a noise that resembles that of a flat spot. But my tires are fine. And when Rollin slowly and I softly apply the brakes sometimes it feels like my abs is kicking in. Have I stuffed up? I have RDA slottered rotors and bendix regular pads.
Any feed back would be good the car is going to a mechanic soon for it's 150k service but it'd b nice to know if it's something normal or such.

Also brakeing feels fine from speed no shudder or anything

thanks

Bendix General CT brake pads (like may modern general street use pads) make use of adhesive friction technology to work properly as opposed to the abrasive friction technology used by higher performance pads designed for repeated high speed use/abuse.

Adhesive friction pads deposit a film of friction material, called the transfer layer, over the surface of the rotor. As the rotor passes between the pads, the film and the pad surface heat up and become sticky. The pads and friction film bond to each other then break apart, absorbing energy. They bond and break apart continuously as the rotor passes between the pads. If the transfer layer is not laid evenly/consistently on the rotor face it can result in uneven friction levels during braking. Over a short period of time the inconsistencies can become more pronounced and give rise to symptoms such as a surging during low speed braking, pedal pulsing and even steering wheel shake at high speeds (I notice that you say yours doesn't have this yet, but it may eventually as time goes on as over a longer period of time this results in what is called disc thickness variation).

Slotted rotors can be more suceptible to this due to the cleaning effect of the slots. While i believe Bendix do say that the pads do not need bedding in before use, the pad and rotor combination should be properly bedded in together so as to lay a consistent transfer layer evenly on the rotor surface.

Check your rotors, and if you see what look to be light and dark patches on the surface or a dark ring around the circumference of the rotor this is the transfer layer. If its patchy, then transfer layer is not even.

You could try cleaning the rotor surface with brake cleaner and then re-bed the system or lightly machine the rotors to restore the rotor friction surface back to original specification.

Sorry for the massive lesson, but I hope this better explains what may possibly be going on with regards to the weird type of brake feel you are getting. I also use Bendix GCT pads with RDA slotted rotors and Swordsman had the same pads with DBA slotted in his EF before it went to heaven :-(. Both cars showed these type of symptons with these brakes.

As for the flat spot type noise, I can only speculate that it may be noise from the slots on the rotors as they pass through the pads...though others on here may be able to confirm/deny this.

I hope this helps.

Matt

[Day-mow]

It sure does. New pad time. Interesting tho I did bed my brakes in. I guess time to try again