Sometimes I actually post useful information. Sometimes.
So, I've kept kind of quiet about it, but ever since I put my Columbia Sports III back together last, uh, November, I've been having trouble getting the hub adjustment right. This is mostly the result of the fact that I experience problems while on a ride, stop to quickly make some stop-gap adjustments, then realizing later that it's still messed up, and just keep repeating the process. Finally, I got fed up with it, and decided to devote some time to getting everything adjusted exactly right.
As usual, Sheldon Brown has the definitive guidance on the subject, but I wanted to make things a bit more explicit and illustrated for you fellow first-timers. So, here we go:
Correct hub adjustment is extremely important. First, it allows you to take full advantage of all three of your gears. Second, it prevents "freewheeling," which isn't nearly as much fun as it sounds. Freewheeling on a 3-speed occurs when the internal gizmos in the hub align so that the pedals can spin forward without engaging the drive. In other words, the pedals are turning, but you're not moving the bike forward anymore. This can be extremely dangerous when you think you're solidly in a gear and pedaling along with resistance and suddenly your legs start spinning uncontrollably. This throws your whole bike/body alignment out of whack and you are certain to at least wobble, and possibly lose total control. Not good for riding in traffic or crossing an intersection, certainly.
Proper adjustment is actually pretty easy, provided you have an ample dose of patience. There are basically only two parts to adjust: the indicator spindle, and the cable tensioner. The indicator spindle is the little rod and chain that emerges from the right side of the three-speed hub. One end of the rod is threaded with tiny threads, and this end screws into the hub itself (see photo). This is where you make your first adjustment.
Disengage the shifter cable from the indicator spindle so that you can unscrew the indicator spindle and take it all the way out of the hub. Check to make sure it's not bent or damaged. If everything is okay, reinsert the indicator spindle and tighten with just your fingers until it stops, then back it off a half turn. This is really important, because if you back it off too much, the indicator spindle doesn't fully engage with the gearing mechanism inside the hub. This was my problem, and caused me no little amount of frustration before I realized it. If the indicator spindle isn't seated properly in the hub, no amount of adjustment to the cable will help.
Now, reattach the cable to the indicator spindle. Tighten the cable tensioner (the barrel on the end of your shifter cable) by screwing it on to the indictor spindle, and use the little locknut on the indicator spindle to hold the tensioner in place. It should look something like this:
Now comes the tricky part. I'll let Sheldon Brown explain it, with particularly important passages highlighted:
For best results, adjust the cable by tension. When the trigger is in high gear position, the cable should be totally slack. Shift down to middle gear, while watching the indicator chain-it should clearly move as you make the shift. Then shift to low gear; again, you should see more chain coming out of the end of the axle. Sometimes the internal parts line up in such a way as to prevent downshifting. If you have trouble getting the hub to downshift, turn the pedals slightly forwards. Once you are sure you are in low gear, take hold of the indicator spindle chain and try to pull more of it out of the axle. If the adjustment is correct, you should be able to get just a tiny bit more movement from the chain. If it is completely taut, the cable is too tight. Make sure to tighten the knurled locknut on the indicator spindle so that the adjustment will stay as you have set it.
Double check the adjustment in all gears. In low gear, you should be able to see that the sprocket moves faster than the wheel, and the hub should not make a ticking sound while being pedaled forward. In middle gear, the sprocket should move at the same speed as the wheel, and you may hear a slow ticking as you pedal. In high gear, the wheel should turn faster than the sprocket. The same slow ticking may be audible in high gear.
If you hold the trigger halfway between middle and high gear, the hub should disengage so that you can spin the pedals forward without going anywhere. If it freewheels forward in high gear, the cable is to tight or has too much friction to release properly. If it freewheels forward in middle gear, the cable is too loose.
If you're anything like me, you will have to make many minute adjustments to the cable tension until you get it just right. The key points again: 1) properly seat indicator spindle in hub; 2) freewheel in high gear means cable is too tight; 3) freewheel in middle gear or low gear means cable is too loose; 4) there should be no ticking sound when pedaled forward in low gear; 5) hub should freewheel between 2nd and 3rd gear.
If you would like to read Sheldon Brown's original article in its entirely, go here. Sheldon also has lots of other great information about three speed (a.k.a. planetary, or epicyclic) gearing, including diagrams that show what's going on in there.
By the way, my experience related here is based on the Sturmey-Archer AW hub that is original to my Columbia, I have no experience with other S-A models or other hub-geared systems.
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