March 15, 2012

On the back of your forty-second screamdown

So, it's only been ages since I last wrote anything in here. While the tumbleweed absent-mindedly blows across the road, and I shuffle around somewhat sheepishly in the knowledge that, incredibly, this blog is actually linked to from somewhere else (edinburghcyclechic, as it turns out, which is suitably ironic for my general predisposition to wear lycra, and occasionally even look good in it), you can listen to the muted and rather pleasant rhythm of cogs ticking round. That isn't the sound of a well-oiled dérailleur transmission, nor even a rusty squeaking one, but of my brain on the realisation that four and a half months have gone by with the first thought that nothing of note has happened.

Has it?

After Tim Brummer at Lightning sent through the replacement and much stronger boom for my P-38, back in May last year, I set off into the countryside here in pursuit of hills and railways and architecture, took a spin down to York to look at Moultons and windmills and railways and architecture, commuting as usual the rest of the time, and all the while generally enjoying the heck out of the bike. After all, it had been several months in which the bike had lain in the garage in a not-quite-rideable state. The first real outing of the new boom had of course been the day of the twelve steepest streets, but it had also cemented itself in my memory as the day that the Brake of Horrendous Squeal came into the world. For some reason the entire world supply of Kool Stop brake pads had vanished a week before, and I'd reluctantly slid in a new set of those peculiar Ashima pads, discovered they were too thick, adjusted my once meticulously set brake positions four times to try to compensate, discovered to my joy a long lost pair of Kools in a bag and slid them in, adjusted the brake position again ... and gone climbin'. And for the next 1000 miles or thereabouts the front of the bike braked just as well as it ever had before, but in the process would be sounding like an air horn.

Slowing down from 20 or 30mph, behind a car, while one's bike produces a noise like a double-barrelled Air Zound mixed with fingernails-on-blackboard, is one of the most embarassing situations I've ever known, even worse than organising a meeting for twenty people and forgetting to invite the chairperson. Worse still, it wasn't even a new situation, as I recalled my experiences of Victoria's old cable-powered Tektro discs trying to do their best in a thunderstorm. They were certainly most trying, which is why I replaced them with Hope hydraulics which turned out to be only slightly more powerful and almost as noisy. But with a P-38 you can have any brakes you like as long as they're rim brakes, so you throw money at it and buy an Avid Ultimate. Given the frankly astonishing increase in price for those twin machined aluminium arms—currently at a discounted 85 of Her Majesty's British Pounds, or £115 at full price, when the Big S's XTR is clocked at £100, and Avid's otherwise excellent Single Digit 7 comes in at an altogether less eyewatering £22—I was inclined to grin and bear it. There was method in the madness at the time I built the bike, because the Ultimate transforms to a mirror image of itself which made for tidy cable routing, and in 2007 we were still enjoying ludicrously good value on expensive components.

In a similar manner to John Ackroyd's Thrust 2, which Richard Noble and Ron Ayres later discovered was stable only under savage acceleration, my P-38 would only be quiet under savage deceleration, and while that might useful for avoiding fading discs or drums, if it had any, I was rather too aware that it wasn't so good for holding traction with skinny little bicycle tyres, even if they've worn down their herringbone pattern micro-tread to pure slicks. The rest of the time, dabbing a brake here and there for traffic lights and traffic jams, an occasional errant pedestrian, or a frequent pothole, the bike squealed unrelentingly. I even found myself digging a heel into the brake arms—sometimes the left, sometimes the right—in a hopeful attempt to quell the vibration, with both brake and rider fretting merrily to themselves.

At least twice I set-to on the bike to resolve the problem once and for all, with a little piece of folded-over breakfast cereal box for presetting the requisite toe-in of the brake pads, and despairingly it made no difference whatsoever. Last week it became all too much and I took Victoria out on the roads instead, while back home I investigated a suspicious amount of play in one side of the brake; the Ultimate runs on two pairs of 15mm sealed ballraces, not that you really needed to know that, so one ought to expect perfection. After prising off a rubber seal and finding all the grease replaced with plenty of rust, it took a heatgun, a hammer and a thin screwdriver to remove the bad ballrace which promptly committed suicide, spilling its insides onto the workbench. And, of course, the things are of a hugely proprietary type that one doesn't find stocked by places like SimplyBearings or Model & Small, being assymetric and of a size far too small for which anyone remotely technical might have any use. But heroically Avid provided a part number—genuine spare parts!—and a few days later again my local bike shop had the goods. Before this I'd actually devised a workaround using industy standard items and some skateboard bits that I would've still had to modify, and then I worked out that it was easier if just as expensive to buy the genuine things in the first place.

Buoyed by my newfound confidence in solving mechanical mysteries, I made a rudimentary Ultimate bearing press and provided a home to two brand new sealed ballraces. I was so confident in fact that my testing regime was to ride 20 metres up the road and back again, and if it didn't squeal I was in business. It didn't squeal.

And so the very next day I set out on my commute. About 30 seconds down the road, where the hill begins, I applied the brake firmly for the first time and my bike was blissfully silent! Actually, it wasn't. At this point I had to get to work, an activity involving plenty of traffic and plenty of hills, so I said something that rhymed with muddy bell and decided my back brake would have to work extra specially hard. Most of that day was spent doing worky stuff, while part of my brain was busy thinking about brake pad compounds and logical ways to rule out one component after another.

As I thought idly about the familiar (too familar, for this former student of vibration theory) relationship of natural frequencies vs. mass, spring stiffness and damping, it occurred to me that my suspicions of why Victoria's discs sometimes sing loudly to themselves, being attached to very lightweight rims and spokes, and akin to a sounding board, might translate to the little bike. After all, I already knew that both wheels were rapidly approaching rim replacement. If the rim sidewall was sufficiently worn down, perhaps that was the crucial factor. It seemed like a good idea to set up the wheel truing stand that weekend and install the new rim I'd bought ages ago while they still made them, and a happy afternoon was spent unpicking spokes and threading them into their new homes, culminating in that meditative zone of spinning a wheel, eyeballing, listening and tweaking things to perfection.

'If this doesn't do the trick,' I said to myself as I returned the wheel to my bike's fork, 'it has to be either toe-in or pad material. It has to be!' With my confidence in solving mechanical mysteries now higher than ever, this time I didn't even bother with a test ride. The next day I set out on my commute, and the first hill was pleasingly silent while the pads gently scoured the untouched brake trake of the rim. I came to the big hill, and accelerated down it. At the bottom, where a bus was setting down its passengers, I decided that slowing down might be a terribly good wheeze. I hauled on the brake, and it squealed for Britain; it was as though the last thousand miles were just the warm up. I may have said several very rude words at that point.

I stopped short of taking my bicycle to the menders, because I used to be one of them and I decided that a stupid little brake couldn't be that hard to sort. Could it? Returning to my bike at the end of the day with my multi tool in hand, I took a bit of plastic about the thickness of a credit card and wedged it behind the brake pad, and reset the toe-in on each side once and for all. It could hardly make things worse. Amazingly it didn't, and even more amazingly the brake suddenly started to behave, just like it did in the olden days. I accelerated, braked, accelerated, braked again, and ... silence. I rode the long way home with the long gradual descent, and it behaved. A few more days and it's still behaving. Hurrah!

I was going to tell you a tale of Carradice, saddlebags and Bromptons, but my back brake has started squealing.


Anonymous said...

I think brake problems are contagious. Immediately after reading about your escapades, the parking brake for my trike crumbled in my hands during a simple tune-up.

Thanks for the laugh, Becky!

Anonymous said...

Hi Becky
I need help with my Speedmachine suspension & I came across your blog.
However, the pictures have gone :-(
Any chance you could put the links back or contact me on
Much appreciated......