M-bar slipping on Brompton: advice?
Lately, I've been having trouble with my M3L's handlebar rotating forward in its clamp whenever I go up the sloping curb of my driveway. Whenever this happens, it prevents me from completely folding the bike (my stubby bar ends hit the brake track, rather than squeaking by the tire). It doesn't seem like my taking the curb is overly abusive, either (walking speed with a 140 lb rider), so that's another source of concern.
So far, I've tried degreasing the clamp area with isopropyl alcohol, shimming the clamp with aluminum, and Loctiting the clamp bolt. Unfortunately, the problem has returned, despite all of these attempts at a fix.
Has anyone else had this issue? If so, have you found a way to get the handlebar to stay put?