Fitting Compact Double on Old Trek
After riding a bunch of new bike candidates to replace my faithful but worn 1986 Trek 400 as my commuter/light-touring bike, I haven't found anything that I like a whole lot better, at least not enough to make me part with $1300 or so. So I'm thinking of taking it apart, cleaning everything up, building up some new wheels, and maybe fitting lower gears.
Ten years ago I added bar-end shifters, fitted a new 7-speed rear cluster with a 32 big cog, and replaced the 39 in front with a 38. That's worked pretty well, but there are big hills where I live, my knees have seen better days, and I'm considering loading the bike this summer and taking a week-long tour. I think I could use a little more help on the low end of the gears.
Since my Sakae SX crank/old-style-spindle BB is original and basically worn out, I could retrofit a triple and get my lower gears, but I've never liked triples and it sounds like this might need new shifters, FD, RD, etc. So how about a 50-34 compact double? Everybody seems to love the R700 Shimano setup and I can pick one up with shimano BB for a pretty good price. AFAIK, my Trek has a very standard 68mm, English thread, 1.37 BC setup for the bottom bracket. Does anyone see any issues with fitting a modern compact double like this? Will the chainrings be on the right centerline for the FD and rear driveline? I'm Okay with fitting a new FD, but I thought I'd see if the old one works first.
Thanks for any guidance.
Your Trek bottom bracket is standard 68 mm English threaded. My 1983 Trek 400 is so yours certainly is too.
I fitted an 8-speed 105 triple crank with the recommended 118 mm square taper UN 72 bottom bracket to mine and the chainline is good and everything works the way it should. I see no reason why the R700 with it's standard bb cups wouldn't work out just right on yours.
The only potential problem is the R700 is spaced for a 9 or 10-speed chain so, even if you are still running a 7-speed cassette, you may need to use a 9-speed chain. Barcons are friction for front shifting so nearly any front derailleur will work. Just be sure to lower the fd to properly clear the new smaller chainring.
Thanks for the help. Am I going to have any issues running a 9-speed chain on a 7-speed rear cluster? Are the cog teeth too wide on the 7-speed for the narrower chain? (I think the reason I only upgraded to 7-speeds on the back from the original 6 was that this vintage of bike has too narrow a distance in the rear dropouts for the modern 8-10 speed setups. I think it's 126mm if I recall correctly. So perhaps my 7-speed spacing is the same as a 9-speed on a modern 130mm spaced cluster.)
Originally Posted by HillRider
I'm running a 7-speed HG-70 cassette using a 9-speed chain, and have no problems at all.