Rear derailleur - nightmere adjusting

Mrdeece

I have a Scott addict with a 10 speed triple dura ace 7800. The problem I have is trying to adjust the rear derailleur so it does not jump and it is proving hard. If I am in the middle front chain ring and try to change from the a large rear sprocket to a smaller sprocket it will often not move until I do two clicks on the STI then it will jump down 2 gears. Ok I adjust so it works but then I get another issue which is: I try to change gear in the smaller sprockets at the back it will simply not change or change but rub. The very strange thing is that I do not get this happening if I am in the biggest chain ring on the front. If I am in the biggest chain ring on the front all the rear gears work fine. I have only done 3000 mile on the bike. I have changed the chain after 2000 miles. All the components look ok. I cannot seem to work out what is wrong. Any ideas?

Monty Dog

For a slow down-shift (i.e. big to smaller sprocket) then the problem is typically due to cable-drag. 7800 in particular is prone to problems due to the concealed cables under the bar tape. May also be due to dirty / poorly fitted / kinked cables. As the bike is relatively new, I'd suggest you take it to your LBS and ask them to sort it out. I expect the cables need to be removed and refitted correctly.

Mrdeece

Good point. I did check the cables by pulling at the inner and it seemed to be free. I think I will change the cables, however is there other things i could check?

P.S. The 7800 does not have the gear cables routed under the handel bar tape.

Buckled_Rims

+1 as Monty says, cables could be kinked or dirty.

The rear derailleur has a natural side pull due to a spring, which your cable is pulling against and locked because of the index. When the cable is released by a fraction of a mm, then the gear changed down a sprocket. However, when there's a bit of dirt in the cable housing it drags or sticks thereby giving no shifting. Sometimes a jolt from the bike will release the cable giving the classic "phantom" shifting a few seconds later.

ChrisSA

I have found with my 7800s I need to change using the bottom of the lever, as opposed to pushing nearer the top./ This gives a definite change vs the will-it won't-it change if not pushed enough.

meanredspider

Monty Dog wrote:

For a slow down-shift (i.e. big to smaller sprocket) .

Isn't that an up-shift at the rear derailleur end? Smaller sprocket = higher gear higher = up?

Monty Dog

Up-shift in gearing, down shift in terms of the direction the rear mech is moving!

meanredspider

Monty Dog wrote:

Up-shift in gearing, down shift in terms of the direction the rear mech is moving!

I'm going to sound like a right bloody pedant but the mech is moving up & out as you select a higher gear (smaller cog)....