The front ball joint on the mirror on Mary’s helmet loosened enough that the mirror blew out of position every time we got up to a decent traveling speed. I’ve repaired these mirrors several times before; they’re plastic and tend to fracture / wear out / break at inconvenient moments.
The first pic shows the mirror (the black surface is reflecting the dark floor joists overhead) with an old blob of epoxy that repaired a break in the outer socket. The socket originally had stylin’ curves joining it to the mirror, which proved to be weak spots that required epoxy fortification.
This time the socket split axially on the side away from the mirror, which released the pressure on the ball socket that seats into it. I found a chunk of brass tube that fit snugly over the socket, then carved some clearance for the existing epoxy blob. The key feature is that the tube remains a ring, rather than a C-shaped sheet. to maintain pressure around the socket.
Here are the various bits, with the reinforcing ring clamped in place. I coated the socket exterior with JB Weld epoxy, slipped the ring in place, and tapped it down with a brass hammer to seat flush with the front face of the socket. That left gaps between the socket opening and the tube that I eased more epoxy into with an awl. A bit more epoxy around the exterior smoothed over that ragged edge.
The strut at the bottom of the picture ends in a ball joint held by a socket that slips into the mirror socket. The loose brass ring above the mirror is some shim stock that I added some years ago to take up slop between the ball socket and the mirror socket and tighten the ball joint. I suppose that pressure eventually split the outer socket, but so it goes.
The clamp squished the outer socket enough to snug it around the ball socket, so when I reassembled the mirror it was fine. To be sure, I dunked the ball in my lifetime supply of Brownell’s Powdered Rosin for a bit more non-slip stickiness.
I have a box full of defunct bike helmet mirrors, dating back to those old wire-frame square mirrors that clamped onto the original Bell helmets. The newer plastic ones just don’t last; we ride our bikes a lot and even fancy engineering plastic isn’t nearly durable enough. A few bits of metal here and there would dramatically improve the results!
I’m going to build some durable wire-frame mirrors, but … this will keep us on the road for a while. I suppose I should make a preemptive repair on my helmet mirror while I’m thinking of it…
The Smell of Molten Projects in the Morning 
Couple of years ago I was in Death Valley with some ‘bent buddies. We trucked the bikes to the top of Devil’s Mountain (Or Dante’s Peak or Mephistopheles’ Mountain) and dropped a vertical mile to the valley floor. We didn’t pedal once and I hit a personal speed record on my Tour Easy by tucking my head behind the fairing: 57 mph. When I moved my head slightly into the jet stream, my helmet mirror vanished.
Since that episode, I’ve run Mirricycle handlebar end mirrors.
david boise ID
I chickened out at 47 mph on a goodly hill down by the Potomac; the thought of a front-wheel flat just kept bothering me.
Mary hates helmet mirrors, so I installed a bar-end mirror on the left side. Turned out she hated that even more, because around here the pavement’s rough enough to render the reflection absolutely useless.
So she’s back to a helmet mirror and I fix the crappy joints about once a year.
My last helmet mirror was more or less a bike spoke bent with the mirror glued to it. It was a commercial product (although I’d be glad to claim it) but the lack of joints and a short moment arm made it stand up to anything I did, even being thrown in the back of the car with piles of other stuff. IIRC the spoke passed through the pivots of two spring clips that clipped onto the rim of my (very old) Bell Biker helmet. Modern helmets are trickier and probably need adhesives to attach to the helmet, but the mirror mount’s still good. My brother commutes to work every day and has something fairly similar that attaches to his glasses: no joints, all adjustment done by bending a 12 gauge steel wire. Now that my girlfriend has a new lower recumbent we’ve been looking for a mirror for her.
My “Bike Junk” drawer must look a lot like yours: I have one of those clip-on mirrors, too!
Poor thing stopped working when helmets stopped having actual shells, but it was perfect while that old Bell lid lasted.
Apart from the rusty springs, of course.