vilinx

Hello,

I'm just starting out doing my own repairs on my bike so I apologize if I don't know the correct terms and such...

I've recently developed a problem that my rear derailleur refuses to shift into high gears. The bike is a 2006 Specialized Allez, 8 speed cassette, 3 ring front. The brifters are Shimano Sora, the derailleur itself is Shimano Tiagra. The cable tension is tight. For the lower gears, when I shift in front the derailleur will click over to the appropriate position keeping tension tight, when I attempt to go into higher (5-8) gears, the cable immediately goes slack (and gets slacker as I shift higher). The derailleur doesn't move out as it should.

Any clues on what I should do to narrow down the problem and fix it?

Thanks!
Vil

Old Hammer Boy

Where is the cable slack? It may be slack between the cable stop on the down tube and the bottom bracket guide, and still be hanging up on the bottom bracket cable guide. Make sure things are clean and free at this point. If the cable has enough slack to the RD, and the RD won't move to a higher gear, it could be the RD needs to be cleaned and lubed, or you may have bent the RD hanger or damaged the RD itself. If the hanger has been bent, your LBS should be able to repair or replace it.

twahl

Take a look at the limit screws to make sure that the high limit screw didn't somehow get turned in on you. If the stop is resting on the screw when the cable starts going slack, you've found your problem, and it's easy to correct.

vilinx

After shifting, the slack in the cable can be seen/felt between the bottom bracket and the rear derailleur.

Vil

Mr. Underbridge

Seems like two possibilities if in fact the cable is slack:
1) Limit screw, as mentioned.
2) Bent hanger.

Option 1) is the best, because you can fix that easily. Try it first - back out the appropriate limit screw all the way. However, if there's no limit screw and no tension, and the derailer's as slack as it can get, then the problem must be geometry - ie, something's bent. Have you whacked the rear end lately (of the bike, that is)? If so, that could be the problem. If you suspect a bent hanger, take 'er to a shop.