(thread title should say "DIY")
Hi all, hoping for some advice on maintaining the “retro” aspect of my bike.
As detailed elsewhere, I commute on a 1984 Trek 520 with downtube friction shifters. Earlier this year, when the obsolete helicomatic rear hub couldn’t be maintained any longer, I got a 27’ wheel from another older bike. However that one had worn-out cogs, on a uniglide hub, and I managed to salvage that by installing five cogs from a new 7 speed cluster (I filed off the wide tab) and for the 6th cog, I flipped the original locking cog around so the “good” side of the teeth would mesh with the chain.
Unfortunately along the way I broke the original Suntour Mark II rear derailleur, and I couldn’t find a similar one on eBay, so I bought a new mid-length Sora rear derailleur. So I have a working 6 speed rear cluster, but spaced like a 7 speed and in fact a slightly better lowest gear than I had before (28 vs 26 teeth).
Things sort of work, but I still have a problem with the chain skipping. I think it is because the derailleur doesn’t work well with the cassette or maybe with the friction shifter. If I am in my highest or lowest one or two gears I have no problem, but if the chain is in the middle of the cassette and I decide to sprint, I sometimes feel it jump – I think it is going sideways, not forward. In other words I think I am getting unwanted shifting under load. However, I’m not sure: I can’t reproduce the problem on my "workstand" (hitch-mounted car rack), because I can’t apply the same torque.
The guiding wheels of the derailleur seem extremely close to the cassette cogs, and also the friction shifting is very tricky…hard to get it precisely where you want it. Also I may have left the chain a bit long to accommodate the larger 28 tooth cog – there’s a bit of slack in the lower run.
Getting to the point: So what do people think the solution is? Is the Sora derailleur not intended to work with friction shifters? Is it possibly mounted wrong? I’m not sure why there’s so little clearance where it feeds the chain onto the cogs. (I can post pictures later if necessary). Would an extra washer between the derailleur and the hanger fix that? It's mounted on a built in hanger with no "claw" part, so maybe it's too close to the wheel?
I'd rather not switch to indexed shifting unless I have to. Would removing a chain link help? Do I need to tear apart the cassette and get slightly wider spacers so the cogs are spaced more like an original 6 speed and not like a 7 speed? Should I post in C&V? Any and all comments welcome