The bike has almost 9000 miles on it. That is way more than any other bike I've ever owned. By comparison, my old Univega has about 3400 miles on it in the 19 years I've owned it. The 3-speed may have more, being 45 years old or so, but I doubt it. It's not a bike conducive to long rides. In the 5 years I've had it it's not even gone 500 yet*.
* Actually, now I think about it, I ride the three speed about 100 miles a year, which isn't very much, but over 45 years it starts to add up. It may have more miles on it than the Univega. Probably not, given that it was in great shape when I got it. The guy who had it before me said he used it only around town, and he picked it up from someone who likely had it tucked away in the back of a garage for a long time. All the equipment on it was original when I got it, even the tires, and they still have a lot of tread. I only replaced them because the rubber was starting to age. So it has maybe a 1500 miles on it at most.
What happens over time is that the metal in the chain and on the sprockets wear on each other. The teeth get sharper and narrower, and the pins on the chain go from rods to spindles. One result is that the chain snugs down deeper into the teeth of the gear. Now this doesn't really make a noticeable difference as far as the gear ratios are concerned, but what one does notice is that it becomes a little more difficult to down shift. Going up isn't much different, because you're sliding the chain down to a smaller sprocket, but to move to a lower gear (i.e., bigger sprocket) you need to move the derailleur arm over a tad further than before to get it over the hump. I'd noticed this issue over the last two months or so, as I was constantly having to adjust the cable tension because merely clicking the shifter to downshift didn't always work. I'd have to either thumb the shifter a little bit more until the lower gear engaged, or else downshift two clicks (which would only drop down one sprocket) then upshift one (only to get the shifter back in alignment with the cassette) to get into the intended gear. Now, I'd assumed it was mostly the cable stretching, and much of it likely was the result of the cable starting to fray, but even now that the cable is fixed and properly adjusted, it still happens occasionally.
BSG explained all this to me, apologizing because he couldn't get it to work perfectly. He said that at some point it'll get bad enough that the chain will start slipping, and when it that happens it'll be time. Unless it really starts to annoy me before hand. I rode the bike last night, and it was fine. Better than it's been for a couple of months, actually.
Besides all the stuff with the drive train, I'd done another repair on Tuesday, also the result of long term abuse of the machine, to wit, the effect my fat ass has on the saddle. I'd been having problems with it for a little while. It's an old "mattress" style saddle, the type that used to be standard on old 3-speeds. Most serious cyclists look down their noses at them**, but I find them much more comfortable than standard saddles. Usually. Lately, it hadn't been so, and it also kept getting out of alignment. The body of the saddle should run parallel to the ground, but it kept nosing down. I assumed (wrongly, of course) that the bolt that clamps the saddle to the post had loosened, so I loosened it further, adjusted the angle of the saddle, and retightened. Then it happened again. Lather, rinse, repeat. Meanwhile, I'd bought a nice leather saddle (one of these), and had been slowly breaking it in***, a ride here, and a ride there, so I started using that exclusively. Unfortunately, it still isn't quite ready, but at this point it was better than the old saddle.
** Of course, these are the same folks who think that adding padding to one's shorts is the solution to riding comfort, rather than just getting a more comfortable saddle.
*** Most modern saddles are hunks of formed plastic with some padding slapped on the top. The padding compresses a little, but the plastic doesn't give at all, so I don't find them comfortable. Leather saddles, and mattress saddles, too, are basically hammocks for your butt. A mattress saddle uses long metal springs beneath some vinyl and padding for support, whilst leather saddles are simply made from a thick piece of leather hung between metal supports. Leather saddles start out very hard, but will eventually break in to mold the perfect holder for your butt while still providing the flex that plastic can't give. In theory. Breaking one of these suckers in takes a long time.
So now I finally took a look underneath the old saddle, and discovered the actual problem. Thousands of miles of supporting the weight of a man much heavier than average had completely deformed the steel rails that connect it to the post clamp. The reason it was nosing down had nothing to do with the clamp. It's that the supports were totally bent out of shape, so much so that they had actually snapped in two places. D'oh!
Fortunately I still had the bike's previous saddle lying around. I've had that one for a very long time, going back to one of my old 10-speeds. It had served me well for years, but I'd had to replace it because the metal supports for the mattress springs had broken. However, the rails were still in good shape, so I swapped them in, and now the saddle is fine. I shall also note that I am now about 60 pounds lighter than I was when I started using the saddle, so maybe the rails will last longer this time around. Plus I still have the leather saddle to finish breaking in. Nice to have options.