Change your brake fluid.

[Ludermilch]

Doing maintenance on my XC brake system I ran into this jewel.

Actually I discovered it residing in my brake lines. It would appear that the previous owner didn't change the fluid as recommended. Once I changed the fluid, I no longer had the shimmies while braking! Wow. Go figure.

[Puppet_Master]

That's Disgusting! Glad to hear you fixed the problem. Stopping is very important.

[dosbricks]

Nice to gain an unexpected benefit from a fluid change. If old fluid thickens down inside the caliper from heat and moisture, it may not flow readily back causing the piston to drag or create the shimmy you were experiencing. Recommended change interval in humid environments is yearly, but otherwise every couple of years is good, or at least when pads are replaced.