Okay, so I’ve got a rather difficult bicycle question that a lot of my more-or-less knowledgable friends haven’t been able to help with. I really want to learn this stuff on my own so I can do my own work, so I figured I’d ask random places like here before I took it to the shop. If the answer isn’t forthcoming, I would also appreciate any book/resource recommendations for me to pick up the finer points of bike lore. I’m trying to dive head-first into becoming a bike enthusiast.
I recently required a 30-year-old Univega touring bike. It’s amazing - way better than the $90 bicycles I’ve owned in the past - but it has one glaring problem. If I shift the minor gears too high, the chain falls off. It can be a little finicky, too, sometimes shifting when I don’t want it to. It was rebuilt a couple of years ago. What I know for sure is that it has a freewheel instead of a cassette, and there was something about the chain being a different width than it used to, or maybe should be. Also, the original freewheel or cassette had five sprockets, and it currently has six.
The previous owner knew about this problem as well. He never took it to a shop, but he got a new derailer, and did all sorts of adjustments on it in an attempt to fix the problem, but with little luck. All of my friends keep yammering on about tightening the derailer, but apparently all of that has been tried already.
One theory the previous owner gave me was that maybe it needs a cassette with five spcorkets rather than six because of the difference in chain width. Does this sound plausible?
I’m really psyched about this bike - I went on a long ride yesterday, and had a ton of fun on it even though I lost the chain a few times, which was annoying because I kept falling behind, so I’m really primed to get this fixed as soon as possible.
Thanks in advance for any insight/resources/discussion people can offer. I really want to get into the whole biking thing.
I know next to nothing about touring bikes in general and nothing at all about yours specifically (I’m an avid mountain biker but barely ever ride on the road), so keep that in mind…
Does this only happen when the major gear is on the far opposite side? It is pretty common for bikes to have problems when you “cross chain” the gears (front gear is on the inside sprocket, rear gear is on the outside sprocket or vice versa). The basic way to avoid this problem if it is cross chaining is just to be aware of the issue and don’t cross chain it. My mountain bike is worth more than my car and it is in great condition but I can still pop the chain off if I cross-chain the gears during a steep climb. It is basically just an inherent problem with the way chain/gear systems work. The impact and frequency of it could easily have been amplified by the modifications you mentioned.
One theory the previous owner gave me was that maybe it needs a cassette with five spcorkets rather than six because of the difference in chain width. Does this sound plausible?
That would increase the chance you wouldn’t accidentally cross-chain, but you can get the same effect by just not using the first or sixth sprocket, when the front gear is in the third or first sprocket (assuming 3 sprockets in front).
Pardon me for stating the obvious, but why not just take it in to your local friendly bike shop and have them take a gander at it? Usually the shop prices are fairly reasonable, and they’ll probably give you an opinion for nothing…
I tend to agree with Coca Cola Zero. A combination of big chainring/big cog or small chainring/small cog should be avoided. It’s also probably unnecessary, as you should be able to get a similar ratio using gears that cause less stress to the drivetrain.
Crossover could be a problem, but I wonder, given the description, how bike savvy the previous mechanics have been. Specifically, what did they do when they “tightened” the rear derailleur? Did they just tighten the whole derailleur on to the hanger, increase the tension in the pulleys, or did they adjust the limit screws?
After ruling out crossover, I’d check the limit screws.
[I]I would look at chain width and the derailleur, and the front/rear gear size.
If I recall correctly, chains are 5, 6/7, 8, 9, 10 from thickest to thinnest. The chain HAS to match the gears. Too thin a chain with too fat a gear leads to the bike not shifting properly.
The issue is one of tolerance build up. On a derailleur bike, the chain NEVER runs straight of thinking about it another way, ALWAY run diagonally relative to the gears. It needs clearance inside for the teeth, so they can both grip and release the chain. It also needs to flex - if it is too stiff, it will tend to shift itself under load, if not stiff enough, the derailleur will need to be too far over, and it will tend to jump 2 gears at a time (overshift).
The clusters have the same problem. The 5 and 6 speed clusters are the same width - so the 6 speed chain had to be narrower to accomodate the closer spacing on the gears…
Likewise, you can cause problems with the front gears with chain clearance. Ultimately running the wrong size chain will wear out the front chainrings. Before that happens, you will have a lot of issues with sticking.
I’m not sure you can still find 5 speed chains anywhere. Hope this helps. t[/I]
Actually, yeah. I mean, I can’t try to implement any of this until after my kayaking trip (which I leave for tomorrow), but I checked back with the previous owner of the bike. The guy had not only tried adjusting it himself, but he had taken it to a bike shop, where they made various adjustments to the derailer screw(s) and other things with no luck. I asked him for more specifics about the history of the chain and cassette, and Kong, it looks like your bike expert is right on the money.
He’d bought the cassette+gears in question years ago, well before having the bike rebuilt and replacing the freewheel. When he did have it rebuilt, they apparently used a narrower chain than what was made for the cassette, because chains the right width aren’t made anymore. So if it’s true what your friend says about the importance of chain width, it looks like a new cassette will fix my problem, because the problem certainly means it doesn’t shift properly.
Anyway, it’s at least worth a shot, and it’s something to tell a bike shop rather than have them waste their time trying something that’s already been tried.
Well, the current one is 6-gear. I’d probably try and get another 6-gear one made for an appropriate chain width. Talking to people suggests that it originally being a 10-speed would have little to do with the problem.
Whoops, poor reading comprehension on my part. Still, I remember it being a minor hassle to find a Shimano 7-speed for my own aging bike, and that was some years ago. And the fewer the cogs on the freewheel, the harder it is to find.
If I understand correctly, the freewheel and chain doesn’t quit match.
Maybe getting the rigth chain are easier?
Looking into the problem I found this:
“Ultra Six ®” spaced 6 speeds used a closer spacing, arond 5 mm. This permitted an Ultra Six ® freewheel to directly replace a standard 5-speed unit on a 120 mm hub.
The key to making this work was the use of a narrower chain. The interior width of the chain was the same as always, but the new narrower chains used shorter rivets, so the ends of the rivets didn’t protroude past the outer chain plates, as the rivets in traditional chains did.
[I]Key for your buddy is that the chainrings, chain, and cassette all have to be the correct vintage / size. Strangely, you can normally use a modern derailleur with ancient shifters, because the detents are built into the shifter, not the derailleur.
There are places that specialize in older / obsolete bike parts. It may actually be cheaper to pay a lot of coin for a chain than to replace the whole system. -t[/I]
So I ended up adjusting the derailleur (with a buddy to show me how) for the hell of it, and it fucking works now. Also, the back wheel was crooked. I don’t know if the wheel is going crooked because of this, or because of wear and tear.
Turns out that every time the previous owner has taken it to the bike shop and had them adjust it, it had worked for a while, but the problem inevitably comes back. No, I don’t know why he didn’t make this clear to me in the first place. So I’m going to ride it for a while and see how long it takes for the chain to start slipping again. But yeah, it’s not a constant problem, it’s a recurring problem.
Update #2!
The problem came back again. This time I found a chain of the proper width and it’s worked fine since a week after my previous post. Roger, your friend’s advice really helped me figure out the problem.
I do have another, easier, question for everyone, though, if you folks don’t mind answering my stupid queries. If my description of everything is too murky, I’ll add pictures.
I need to tighten my brakes. By inspection, I saw two methods of accomplishing this.
First: the bike cable passes through a metal “dingus” that is attached to the U-brakes by a loop of thick wire. Braking pulls on the dingus, and closes the breaks. Pretty simple. I unscrewed a bolt on the “dingus” (it was pressed against the cable, holding it in place), pushed the U-brakes to the wheel rim for some slack, slid the “dingus” up along the cable, and refastened the screw. It certainly affected the tension, but it was difficult and awkward work, and the brakes are still looser than I want them. Is this something a newb like me should be messing with? It’s the brakes, so I want to be paranoid in my inexperience.
Second: I don’t think this bike has an adjustment barrel. There are none on the handlebars. At the rear end of the housing, there is a screw with a hole in it through the frame. Loosening this screw naturally DOES end up tightening the brakes further as it pulls on the cable, but my doubting inner voice tells me that if it were meant for adjustment it would have some sort of safety clip for stability while in use.
Go with the first way. There is a special tool thats designed to pull the brake cable I’ve used one and they are really nice though the job can be done with a pair of pliers.
