I just came back from a quick ride on my 1968 r60/US with 33,000 miles . When applying the rear brake, I would get a metallic squeal from the rear whel. ..only used the front for the ride hoe! Luckily it was a short country road ride. Before I take off the Old European bags to remove the wheel, how can I adjust the brake .I assume it is via the threaded rod on the right side of the wheel.
Keep in mind the squeal may be dirt-related. You may need to remove the shoes for cleaning and clean the drum as well. This may or may not resolve the problem. Sometimes you need to replace the brake shoes themselves.