Like most bike geeks out there I am occasionally approached by my non-bike-geek friends and asked if I can take a look at their bike. I’m always happy to work on friends’ bikes, but they’re usually not bringing me their much loved Ibis Mojo. I usually get the “but it was the top of the line bike at Wal-Mart and it cost me $100” bike, or bad mojo. I really don’t mind working on these bikes, even though it may not have been ridden in five years and chances are it won’t be seeing pavement for another five. Maybe this time they’ll decide to ride more often and get hooked on cycling like I am.
This bike was different though. Sure, it had some dust, but nothing that would keep me griping about it ( I tend to gripe about things ). Why was this one different from the bikes I usually work on? First, it is a ten speed Schwinn Suburban, and after an internet search I was able to trace the bike to a May 1978 production date. Second, the rear derailleur is a Positron ll, Shimano’s first foray into indexed shifting.
Because my home mechanic skills are limited to geared bikes built after 1983 I had not encountered Shimano’s Positron system. The five rear cogs are all in a fixed position ( the large cog being skipped tooth ) and the freewheel is located in the cranks. In place of a spring, the Positron uses a solid cable to accomplish the shifting, and the detents are built into the derailleur, not the levers. What this drive-train allows a rider to do is to shift while coasting. Any ideas on why this wouldn’t be a good system for current mountain bike applications?
Lucky for me, this bike had little mileage and was well taken care of. I only had to true the wheels, repack the hubs and replace the tires. With the shifting and braking still working smoothly ( after 30 years ) I decided to leave well enough alone. Why, if it’s still working, tear into a potentially irreplaceable part.
While this bike is unique to me, I found out Schwinn Suburbans were quite common and don’t hold much value. That aside, I think these bikes make great townies and I’m going to keep a look out for one of my own.