After flipping a coin to decide whether to post this here or in C&V...

I've got a 1970s Peugeot UO-8 with Mafac Racer brakes. If I adjust the brake pads on the front brake so that they're aligned with the rim's brake track, I find that flex or play in the brake carries the brake pad up into the sidewall of the tire during braking. The attached pic isn't mine -- I stole it from someone's blog -- but it shows the problem exactly.



For now, I've adjusted the pads so that they come to rest on the brake track during braking, much like in the attached picture. Is there something I can do to the brakes to eliminate or reduce this flex? The flex appears to come mostly from the arm's pivot point, but there's not a lot of play when checked by hand with light-to-moderate force. I've checked to ensure the bolt holding the arm is tight.