Rear Derailleur wont shift to larger gears
 

I am tuning my bike up because I am taking it to college with me. I have ran into a problem however. After doing some research I am still confused. What happens is I loosen the bolt that holds the cable into the derailleur and I turn my gear shifter so that it is in the smallest gear. Then I go ahead and I tighten the cable and screw it back on. Everything is nice and tight at this point. Then I lift the rear wheel up to pedal and switch gears. Immediately after switching gears I get a lot of play in my cable and it will not shift to the larger gears. Any explanation/help would be much appreciated.

Are you sure the bolt is tight enough? It sounds like its slipping.

What derailleur? Also, what do you mean by "smaller and larger" gears? Are you referring to numbers (i.e. 1, 2, 3) or physical size of the sprockets?

I think you're doing it the wrong way. Your derailleur should be in the HIGHEST gear (i.e. smallest sprocket) when it has no cable tension on it. The corresponding position or number on your gear shifter should be the HIGHEST number.

So if your bike is a 7 speed, the shifter should be on "7." If it's 8 speed, the shifter should be on "8" and so on.

It sounds to me like you're attaching the cable at the derailleur when the shifter is in gear "1." So when you change the shifter to gear "2" it is releasing some cable, but the derailleur can't move any further, hence the cable slack you're experiencing.

Another theory is that you may have a low-normal derailleur. When a low-normal derailleur has no cable tension, it defaults to the LOWEST gear/largest sprocket. So if you're connecting the cable with the derailleur in its default position, but the shifter set to the highest gear, this would also explain the problem.

BUT I'm betting that the first scenario I explained is the problem, although we can't be sure until you tell us what derailleur it is.

So questions:
1: When you disconnect the cable and turn the cranks, which gear does the derailleur automatically shift to?
2: When you're attaching the cable, what gear position is your shifter set to (i.e. 1 or 7/8/9?)

Go to the Park Tool site, they have a great tutorial on adjusting a derailleur.

Sounds like you have your shift lever in the wrong gear when setting up. See above/\

Despite pulling the cable "tight" when you attach it to the clamp bolt, you aren't getting it tight enough. All modern rear derailleurs have a cable adjustment thimble at the derailleur where the housing enters.

First set the shifter to the smallest cog (highest gear). Thread that thimble all the way in, then pull all the slack out of the cable and tighten the clamp bolt. Try to shift from the smallest to the next larger cog. If the shift isn't clean, unthread (counterclockwise when seen from the back) the thimble 1/2 turn and try the same shift again. Keep adjusting until the smallest to next larger cog shift is clean and reliable. The rest of the shifts should be good too but some minor tweaking of the adjustment thimble may be needed.

Watch this....
http://www.youtube.com/watch?v=Skzvf...eature=related

I think this will help you.

I have put a mark on the bolt and it is not slipping. The slack seems to be coming from the gear shifter.

1: When you disconnect the cable and turn the cranks, which gear does the derailleur automatically shift to? the smallest (physical)
2: When you're attaching the cable, what gear position is your shifter set to? number 1

So it's indexed. Put it in your highest number and then try it.

Yep, try it in the highest number.

Another thing to check on is making sure all the cable ferules are seated in the cable stops. If they're hung up on the edge of the stop when you pull and set cable, they'll eventually settle into where they're supposed to be and the cable will be slack at that point.

Shift to the smallest rear cog first, THEN loosen the clamping bolt. Then follow the Park site procedure. If your cable housing gets out of place and is not seated properly when you pull the cable tight then you can get slack after you shift back and forth.

THERE'S your problem.

The shifter needs to be set to the highest number.

So now what you need to do is disconnect the cable, allow the derailleur to move into the highest (smallest) gear. Click your shifter into the highest number. Now attach the cable, pulling it tight so there is no slack. Now, as "Hillrider" suggested, use the barrel adjuster to tune it up.

Check some of the tutorials/videos which other people have posted to get a better idea on how to do this.

For a first timer, it can be a bit fiddly and tricky, but it's easy once you get the hang of it ;)