Wednesday, November 26, 2008

Schwinn Sports Tourer Build: Drivetrain

When I moved from my battered old Raleigh to the shiny new Shogun, and then from the Shogun to the Kestrel, each step represented a leap forward in the quality of shifting. The Shogun was my first taste of reliable indexed shifting. And with the improvements in the derailleurs, shifters and rear cassette design that came with the Kestrel, shifting became rapid, skip-less and effortless.

In building up my Schwinn, I really had no interest in moving back to the dark ages of shifting. I wanted the drivetrain to perform like a bike from 1992, not 1972. Even in 2008, that's a pretty good thing (and actually it makes me think that I should go ride a current road bike to see what the state of shifting is like today). So what did I do? Well, I bought a bunch of 1990's Shimano drivetrain bits and put them together on the Schwinn. And I learned a lot in the process.

I've listed most of the bits before -- 105SC hubs, crankset and front derailleur, 700CX rear derailleur (long cage), 7-speed shimano cassette, SRAM chain, and I actually started out with Ultegra 8-speed bar-end shifters. During the initial drivetrain installation, the only thing that stymied me was that the seat tube was a little too large for the clamp-on Ultegra front derailleur I'd bought for the bike. I could almost get it around the tube, but tightening the bolt was going to either remove some paint paint, or more likely crimp the tube or snap the derailleur's clamp, none of which was on my list of goals.

So instead, I bought a slightly oversized clamp-on derailleur mount to adapt a braze-on front derailleur to the bike. I had the Kestrel's original front derailleur in my parts box, so that made making that shift easy. And three strips of aluminum flashing shimmed the clamp so it gripped the seat tube tightly enough. In truth I first shimmed it with two strips of thicker copper flashing. But the clamp is aluminum, and I eventually remembered that you're not supposed to have aluminum and copper touching, or they'll corrode. Not a big deal to swap out, though.

The maiden ride on the bike was with all those pieces in place, and the picture from a few posts back (of the bike in front of the rhododendron) was in that state of build. The only problem is that this configuration didn't work very well, and not only in the drivetrain department.

I'll get to some of the other issues later, but there were two main drivetrain problems. First, I couldn't get the 8-speed indexing to work right with the 7-speed rear cluster. I'd read (I think on Sheldon's site) that the two were pretty close, and that you could usually just set the adjustments up so that the last click was wasted and everything would work OK. Not so, in my case. I was never able to eliminate all the chatter that signals a misadjusted derailleur cable, and I'm very sensitive to annoying misadjusted derailleur cable clicking. For a while I turned off indexing on the shifters, and that of course let me trim the derailleur properly. And since I was living un-indexed, I eventually swapped them out to try out retrofriction units. What I've found since, is that I actually like non-indexed shifting just fine -- it's the smoothness of the gear change that's most important to me. And one of these days I'll try the retrofriction bar end shifters available from either Rivendell or Velo-Orange -- the Suntours are a little stiff.

The second problem was more vexing, and it's not often you get to use the word "vexing", is it? Anyway, the second problem was that the derailleur wasn't maintaining correct spacing, relative to the cogs. Remember that the function of a rear derailleur is to engage the chain with a specific sprocket of the rider's choosing. And the guide pulley has to sit in the right place, relative to the engaged sprocket, for the derailleur to do its job well. So this is pretty important stuff. On the Schwinn, the guide pulley was basically riding right on the cog, especially the largest one. It shifted OK, but it was noisy and struck me as a recipe for premature pulley wear.

I'd never had to use one, but I knew that derailleurs have an adjustment screw to properly position the guide pulley, relative to the sprockets. So the first thing I tried was to adjust the derailleur positioning screw. It didn't seem to help much, so I went out and bought a longer screw. Still no help. So I flipped the bike over and watched what happened with the screw when I adjusted it, and I found that the screw was angled such that it just overshot the little flat spot on the dropout it was supposed to engage with. The screw was doing absolutely no good at all. I tried a couple of things, including taking the screw out and threading it into its hole from the front, hoping the head would hit the right spot on the dropout, but that didn't work either.

I went online and eventually discovered that the Huret dropouts on the Schwinn were not consistent with the modern standard for locating the derailleur adjustment flat. I may have interpreted things incorrectly, but I think it basically said Campagnolo's standard for dropout shape ultimately prevailed, and everyone uses that spec today, including Shimano. On the Huret, that flat is maybe 30 degrees further forward, relative to the derailleur pivot bolt, which was far enough to render the adjustment screw useless.

One site I found showed some adapters that used to be available so that Campagnolo derailleurs could be used with Huret dropouts. Ah-ha! I shut the laptop and let my brain chew on the notion of an adapter for a bit. I ruled out trying to braze a wedge of metal to the flat to pull it rearward where it was needed, if only because I don't have any brazing equipment and don't know how to braze. I also ruled out trying to find an appropriate Huret derailleur, because I wanted the modern shifting quality of current Shimano bits. The adapter idea seemed to be the best option. I sketched out a couple of things involving fender washers, but was concerned about being able to cut and bend one with any accuracy -- they tend to be kind of thick, and mild steel also tends to rust.

Then a picture of the pile of screws and washers I have out in the barn popped into my mind, focused on a funny-looking plumbing washer I had. It was kind of like a fender washer, except in very thin, chromed brass and with two flat sides. Kind of shaped like a capital "O" in an old monospaced typeface or something. I walked out to the barn, grabbed the washer right off the pile where I'd pictured it, grabbed my tin snips and a small pair of pliers and started cutting and bending. No more than 5 minutes later I was looking at the thing in the picture, less the ragged center hole, which I hadn't yet drilled out.

Adapter in hand, I went back out to the barn, took off the rear derailleur and tried to fit it over the derailleur mounting bolt. The hole was a little too small to go over the bolt, so it was enlarged on my drill press (it got out of my vise in the process, which is why it looks so terrible in the picture). Ragged or not, this time it fit on the derailleur, and when I bolted the derailleur down, everything pretty much lined up. I had to tweak the folded tabs a bit to be more radial to the hole, but it fit perfectly otherwise. While I had it off, I took the picture, then cleaned up the snipped edges with a file, and it went back on the bike where it sits today, undisturbed and working invisibly to properly position the derailleur.

Now the cool thing for me is that I did all of this freehand. No measuring, no planning beyond a sketch, all freehand cutting and bending, and only the slightest bit of fitting during installation. I didn't even take the derailleur off the dropout to eyeball everything before I made the part -- I just grabbed the washer and started cutting and bending. Not bad, eh?

The only other thing I've really fooled with on the bike are pedals. I did the original build with Look road pedals. But as soon as I remembered how wiggly my daughter was on the trailer bike (especially this big, dramatic one -- you'll notice the look of suffering on her face in such an idyllic location), it occurred to me that trying to hold us up at a stoplight with only a hard plastic triangular contact patch on the pavement probably wouldn't have been the smartest thing to do. So I swapped those for some Look mountain bike pedals I have, which use SPD-compatible shoes with normal rubber soles. Those worked pretty well, and gave me plenty of grip. But the shoes always make my toes fall asleep in short order, and that didn't seem like a lot of fun for longer rides that were part of my mission for this bike.

Then at some point I read Grant Peterson's post about cycling shoes, and just loved the utter contrariness of it all. I just couldn't resist changing things up a bit to see what Grant was talking about. I bought a pair of Rivendell's Grip King pedals, and gave them a try with a stiff-ish pair of Teva's I had kicking around. The jury is still out for me on the whole unclipped pedaling experience. It has advantages in some situations, but I find my feet slipping forward off the pedals at the top of the stroke. I may not be pedaling in 360 degrees, to Grant's point, but my stroke has adapted to being clipped in, just the same. For now, I'm keeping them on the Schwinn, but on my other bikes I'm sticking with my Look's.

So quite a bit of discovery in here, about the bike, about component compatibility, about my own ability to fabricate stuff, and about different approaches to riding. As to the challenges -- in all there was nothing truly difficult, it felt good to solve these problems. Still does, in fact.

All for now,


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