After much research and spending time reading the Turkey Gobble Mega Thread, I see that my problem is common to Avid brake users.
To save the next poor soul from having to dig into a 580+ post thread, here is a summary what I have found about brake shudder / judder for Avid brakes.
I don't have a gobble problem, so this is all about shudder.
The reason for our woes is resonance. Either from the brake system or from the combination of the brake and the frame. People have experience transferring the same braking system to another frame and not having the problem. Resonance exhibits itself at specific speeds and with specific equipment combination. Changing something in the mix can change the strength of the resonance or completely remove it. Something in the system is acting like a tuning fork. Therein lies our predicament.
Cheapest and easiest - If your bike is under warranty, call SRAM. They know the problem and will send a fix, with your LBS acting as liason. The fix may or may not work, and your LBS may or may not comp the work done. What is certain is the parts will be free.
SRAM tech bulletin
FREE fix - align the calipers or align the rotors, or both and torque all the brake fasteners. Chances are you will change something that will change the resonance properties of the braking system.
Fixes requiring parts/supplies - change something in the system. One or a combination of the following will change the resonating frequency, hopefully beyond your riding range:
- resurface the pads by lightly sanding them. I used 400 grit sandpaper. It helps to do it on a glass surface to get a good flat surface.
- apply a thin layer of copper grease on the BACK of the brake pads.
- file the rotors for burs or scrub it with steel wool.
- change the height of the calipers, using washers, in relation to the rotor for better contact
- change the pads to organic or Kool Stop
- change the rotors to a different size or brand
- put a lead weight on your noisy caliper
The Warren Buffet Fix - change the whole braking system with the hope that the new system will not resonate on your frame. Shimanos and Formula users seem to have less judder problems.
As it is, I am waiting on the SRAM fix before I start spending money. The vibration seems to be harmless, at least in my case. All I get is a shudder when descending at very slow speeds while braking.
I changed the title of the og post for easier search hits.
Thanks for the info MTBR!