Straight up: this is about a stainless steel socket head cap screw I installed eight years ago, not the original Easy Racers screw, so this is not their problem.
I rode out for milk-and-eggs at the corner store, a flat one-mile ride, and stopped at the traffic signal. Light goes green, line of cars accelerates, so do I… and there’s a snap and the left side of the seat sags backwards. I am not a powerhouse rider and it’s March, so I’m not doing leg presses while getting up to cruising speed.
I continued the mission by sitting slightly to the right on the seat and pedaling gingerly, then diagnosed the problem in the corner store’s parking lot. If I’d been further away, I’d have done the repair right there, but I figured it’d hold together until I got home. It did.
The problem turned out to be a broken screw holding the left-side seat strut to the threaded eyelet on the rear dropout. The top picture shows the way I have it set up: seat strut clamp outboard, rack strut inboard, with a socket head cap screw extending all the way through, and secured with a pair of stainless nuts that went missing along with the broken screw end.
Here’s the fracture across the end of the screw, which shows no evidence of foul play. As nearly as I can tell, the whole thing snapped off in one event, with none of the crud that would indicate a progressive crack. Compared with that wheel stud, this is in pristine condition.
So it’s time to replace the right-side screw, as well, which means a trip to the Bike Repair Wing of the Basement Laboratory. While I had the bike up in the repair stand, I decided to reshape the head on the right-side screw for better chain clearance.
As nearly as I can tell, the usual practice puts both the seat strut and the rack strut outboard of the threaded eyelet on the dropout, but that seems wrong to me. The seat strut puts a tremendous amount of stress on the screw, so you really want that lever arm as short as possible: put the clamp against the eyelet. While the rack isn’t as heavily loaded, cantilevering it outboard of the clamp just doesn’t look right.
But putting the rack strut inboard of the eyelet means the screw head sticks out rather more than I’d like. Very rarely, the chain will snick against the head and even more rarely it jams between the head and the freewheel. Nothing much happens (it’s a freewheel, after all), but I think reducing the head thickness ought to help.
So I chucked the screw in the lathe, shortened the socket by about half, and put a taper on the head. If I had a stock of round-head cap screws, one of those would be even better.
The shortened socket makes it a bit tricky to get enough bite with the hex key, but this isn’t something that requires much attention after it’s installed… and I get to do all that in the shop.
Dabs of Loctite in the eyelet and nuts, for sure!
By a truly rare coincidence, a standard 1-1/2 inch cap screw is exactly the right length.
Here’s a view of the installed right-side screw, looking rearward along the upper rear triangle tube. Seat strut to the outside, rack strut to the inside, and reshaped head above the cluster.
Took the bike out for a 16 mile spin today and it’s all good.
A note for the weight weenies in the crowd: a rack on the back of the seat adds a redundant support structure. Without that, a failed seat strut can be a real showstopper. Even if you don’t use your bike as a pack mule, maybe you should add a rack.
Memo to Self: add more nuts to the tool kit!
The Smell of Molten Projects in the Morning 
You clearly did the right thing by loading the bolt the way you did. In aircraft parts, stainless steel cable is somewhat-to-considerably less strong than steel that’s been galvanized, maybe up to 30% weaker, so it might be possible that you could find a cadmium-plated high strength bolt that would do better than the stainless one. I know you live in a place where stuff actually rusts, so there’s a strong incentive to use stainless.
The whole notion of bracing the seat on those little threaded hoodickies bothers me, but that’s the way they do it.
Our young lady’s Tour Easy has two eyelets on each side: one for the seat and one for everything else. That’s better.
I still think it’d be better with a serious clamp around the tubing or a much larger fitting, but nobody seems to have any actual trouble with them, so I’m just a worrywart.
you live in a place where stuff actually rusts
And how! Galvanized steel simply rots away; I learned the hard way not to use that on the bikes.
Of course, if I’d actually clean the crap off occasionally, the stuff might be much shinier. But I vastly prefer riding to licking the fiddly bits, sooo …
cadmium-plated high strength bolt
This is still permitted? Why have I not been informed?
Given the furor over NiCd batteries, I’d imagine that cadmium-plated bolts are prescription-only items, right up there with other controlled substances. Unless you’re the military, in which case it’s probably OK.
With that in mind, I found some of those in the basement…
Ya know what’s weird: up until the late 1990’s, they were still selling cadmium-plated bits, and by that I mean the thing you put in a horse’s mouth right against its tongue. I never did understand that.
I hadn’t realized until just now that the nice yellowish coating on grade-8 bolts is a zinc plating thinner than galvanized. That’s not going to do you a bit of good. Hrmph.
the thing you put in a horse’s mouth right against its tongue
I knew there was a reason I didn’t like horsemeat…
You betcha they are: http://www.aircraftspruce.com/menus/ha/bolts.html. All sorts of fun things that people think are banned are still allowed and widely used in aviation — tetraethyl lead, Halon, …
still allowed and widely used in aviation
One of the few places where performance counts more than stylishness: if it doesn’t perform, it doesn’t get off the ground!
But, at a buck a bolt, I think I’ll continue to eke out a miserable existence with stainless…
Speaking of getting off the ground, I’m waiting for a plane to fall out of the sky due to tin whiskers in the avionics. Folks are starting to notice that banning lead in solder has consequences, but there’s a whole generation of aircraft with literally flaky electronics up there. Sigh.
You say that now, but what if eight years hence you’re doing 60mph on a downhill?
Very few airplanes actually rely on avionics to stay in the sky, and those that do are at a minimum triply-redundant and actively-monitored, so I wouldn’t worry too much. And tin whiskers have been very much in the forefront of people’s minds in the aerospace industry, having been a Big Deal for satellites and such for a very long time. And most avionics and military suppliers are exempted from RoHS anyway…
what if eight years hence you’re doing 60mph on a downhill?
Well, then, I’ll just say something really expressive…
But I ain’t pedalin’ for diddly on the downhills: I’m hunkered down behind the fairing with a terminal case of SEG.
Not to mention I punk out at about 40 mph, figuring something like a front-tire flat would do me absolutely no good at all.
at a minimum triply-redundant and actively-monitored
Except that airplanes are so safe that all the accidents nowadays are amazing concatenations of “it can’t possibly happen” conditions. Sort of like whatever ate Air France 447…
>Not to mention I punk out at about 40 mph, figuring something like a front-tire flat would do me absolutely no good at all.
I think about that a lot. See, I have my cyclecomputer set to metric, and it only has two digits, and we have an awful lot of enormous mountains around here… so it’s not too difficult to go infinitely fast, but the *wisdom* of going infinitely fast is difficult to explain. So far, no blow-outs, but I have spent some time on radial trueing of my wheels. Out-of-roundness is unpleasant at 30mph and terrifying at 50+mph
Out-of-roundness is unpleasant
As is out-of-balance. For a while, back in my upright bike weight weenie days, I actually balanced out the valve stem with lead solder (gasp) weights distributed on the light side. It worked surprisingly well, although I eventually realized how little payback it provided for my usual riding style…
These days I just use reflectorized sidewalls and let the (Presta) valve stem take care of itself… and use a Park tension gauge on those rare occasions when I must build a wheel. Works great!