Monday, May 25, 2009

Derailleur Swap for Schwinn Sports Tourer

The derailleur situation on my 1972 Schwinn Sports Tourer has been sub-optimal since I finished the build a year ago.

When I first built the bike up, I used a mix of early 1990's Shimano derailleurs. At the rear, I had a Shimano 700CX derailleur, which appears to have pretty much the same quality and design as a contemporary 105SC rear derailleur -- painted aluminum outer parallelogram link and knuckles, stainless inner parallelogram link and cage and unsealed pulleys. And at the front, I used a 105SC braze-on derailleur (the one that came with my Kestrel), mounted to an oversized and shimmed Shimano braze-on adapter clamp.

How was this sub-optimal? Well, both derailleurs worked seamlessly within the range of their design. The long cage of the rear derailleur wrapped enough chain to support the broad spread of gears I'm running, and the functionality of this part was as flawless as I've experienced with any recent Shimano derailleur. But the maximum cog limit of the rear derailleur was more like 30 teeth than the 32 I'm running, so there was a lot of noise (and probably wear) in the lowest gear, as the guide pulley rode right on top of the first cog.

Up front, there was no functionality problem at all, but what I'd cobbled together certainly wasn't elegant. A standard Shimano clamp-on front derailleur made for 28.6 tubing doesn't wrap around the slightly oversized Schwinn tubes, you see, and I didn't want to either break a clamp or crimp a tube. So I went with a way oversized adapter and shims, and it worked just fine as I said. But it tugged at me.

So over the past few months, I've been scheming. I bought a set of Suntour derailleurs a while back. The rear was the Superbe Tech you can see in the photo from my last post. And the front was a Superbe Pro with the band-type mounting system I first encountered on the Motobecane Steve gave me. I wasn't familiar with these prior to that encounter, but essentially there's a chromed strap that wraps around the seat tube. The strap is sized to fit the seat tube and held together with a stud that serves as both a pin to clamp down the strap and a mounting point for the derailleur body. Seeing this on the Motobecane, I incorrectly guessed that these were one-size fits all, or somehow adjustable. I discovered that wasn't the case today, but even so figured I'd have better luck making one of these fit a Schwinn seat tube than a cast aluminum clamp. And indeed, it wasn't a lay-up, but it only took a few moments of fiddling with a pair of pliers to get the Superbe Pro front derailleur to fit.

That's the front. At the rear, I installed a Shimano XT derailleur, which has a maximum cog size of I think 34 teeth, so it works great with my rear cluster. While I had the old derailleur off, I inspected the brass shim I'd made to adapt the Huret dropout to modern derailleurs, and it looks no different than when I put it on. Works fine with the XT derailleur, too, as expected. The other thing of note about the rear derailleur is that it's a Rapid Rise model. That means the spring in the derailleur body pushes, rather than pulls, so at rest, the derailleur wants to be in low gear, rather than top gear. The effect of this is that it reverses the orientation of your rear derailleur lever. So with my Suntour ratcheting bar-ends (which work really well with this derailleur, I've already found), pulling up on the right lever shifts up, rather than down. It's a little odd, I have to admit, but I'm sure I'll get used to it. I have three basic shifter layouts in operation in my fleet anyway, so remembering that the bar ends work one way vs. another way shouldn't be a big deal. However, if I'm coaching Juli, I'm going to have to remember what "go up a gear" or "go down a few gears" means on her bike.

My ride today was on the Kestrel, and I only made a quick test run up to the next driveway to make sure I didn't screw anything up. So far so good, but not a lot of data yet. I'll learn more on my ride to soccer next weekend with the girls, weather permitting.

I'd also be interested to hear what others have done with these bikes, in this department. Anyone else tackle a modernization of one of these great old tanks?

While I was at it today, I also swapped the Ultegra rear derailleur on Ava's trailer bike for a similar but more beat-up unit. That one works fine, but the rear adjuster barrel is kind of hosed (the threading in the knuckle is messed up). Since she's not running indexed shifters, that's NBD, but I can unload the one I pulled off on eBay for more than I'd get for a damaged one. I'm still clearing out my parts box, so that's one more part to list.

All for now,


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