I have known it's time for a brake job on my R50 for quite some time, I have a light pulsing when I brake. However, out of the blue last week, I eased into the brakes, and I get a very loud "clunk" with every rotation of the wheel, and a terrible pulsing in the brake pedal, coming from the passenger side rear. I'm going to put it on stands today and see what I can, but initial observation didn't show anything obviously loose etc. This problem arose immediately, as if something just "let loose".

Any advice on where to look first?

 

Moving you to the Stock Problems/Issues area.

Did the brake sensor trip? The sensor is on the passenger side rear (driver side front). Would think if you got a clunk when you braked that something was moving around. Suggest you check all your suspension attachments.