That reminds me, I meant to suggest you try a dilution of Simple Green. Try 50:50 water:Simple Green. Squirt on, agitate with a nylon bristle brush and hose off. There’s different brake compounds and different alloys and they react differently so it may or may not be effective.
If it doesn’t work you can always increase the concentration but I’d do it in an inconspicuous place first just to test it.
Other people use baking soda made into a paste, it’s not something I’ve tried on decorative part of a car or motorbike myself but I have used it to clean soaked in blackened grease off aluminium castings. I’ve had other bike riders use it to clean rims so it might work. With the castings I washed them off afterwards and then dried them before giving a liberal spray with WD40. I find it soaks into the top layer of uncoated alloy and helps stop other muck soaking in.
