The mountain bikes that I've ridden in the past have used a derailer system: you have several cog wheels, of varying sizes, then a claw pushes the chain from one to another. I assume that the idea is to vary the length of the chain, but I'm not sure of the details. Anyway, that means that it's fairly easy to fix a problem: just pick up the chain and hook it over the appropriate cog. (Disposable gloves are handy for this, so that you don't get oil all over your hands!) My Brompton uses "hub gears" instead, and I'm a bit more hazy about them; moving the gear lever will adjust the tension on a cable near the back, and that seems to tug a piece of plastic up and down.
Coming back to Wednesday, I continued my journey in third gear, until the aforementioned cable came apart completely. I could still ride the bike after that, but I think it just chose its own gear, since there was nothing to hold the chain at a particular size. My boss showed me how to repair it, and I got back to the state I was in on Monday, i.e. second/third worked ok, but I still couldn't get into first. Last month, I said: "One slight quirk of my bike is that I have to be pedalling fairly fast in order to change gear." Speaking to my boss, it turns out that he doesn't have this problem; in fact, he can change gear without pedalling at all. So, I think my gears have actually been having trouble for a while, without me realising it.
According to the Brompton website:
"Once any initial cable stretch has been taken care of, hub gears should seldom need adjustment. However, if you notice any slipping or other odd effects when pedalling, deal with problems as soon as possible to avoid permanent damage. Usually the problem will be caused by poor adjustment, but it could also be caused by a stiff cable run or damage to the little chain which goes into the rear axle. If you cannot resolve the issue quickly, avoid hard pedalling in the gear in question and take your Brompton to your authorised dealer."
I thought about taking it into the shop on Thursday morning, but I didn't know how long they'd take to fix it, and I basically rely on the bike to get to work. Instead, I made an effort to cycle gently on Thursday/Friday, then I took it back to the shop (Bigfoot Bikes) today. As it turned out, they were able to fix the problem very quickly, and they didn't charge me anything for it, which was remarkably kind of them. This is the same shop that I bought it from in the first place, and I've been back there a few times since; it's not the closest shop to where I live (or work), but I'm impressed by their customer service. The only problem was that I didn't see how they did the repair (the mechanic took my bike into their workshop at the back). They are on the LCC list of people who run maintenance workshops; they don't have any more planned at the moment, but I've asked them to contact me if they do restart them.
While the mechanic was checking my bike, he suggested that it's due for a service. I agree, although I think it makes sense to synchronise that with other maintenance work. Following on my previous post (where I pondered a trailer), I've asked them to order a rear rack and "Eazy Wheels", then they can install that and do the service at the same time. The only snag is that I may need to replace my rear mudguard at the same time; there's nothing wrong with it, but apparently there are different versions for with/without a rack. So, it would have been cheaper to order the rack when I first bought the bike, but never mind.
Anyway, time for an early night - I'm out on the ambulance at Notting Hill tomorrow.