Setting rear gears - Inconsistant cable tension

[PaulSecteur]

I have been looking at a bike for a friend of a friend.

Its full 105 5700, about a year old.

The problem he is having is that the gears on the rear cassette cant be set right. I had a look and found that when I set the cable tension right for it to change up the gears with one click, one change(from small cog to large) it will change up as it should, but to get it to change down I have to release the cable tension but about a turn or it will skip cogs on the way from large to small.

It seemed like there was some friction in the cables, so I cleaned them out with a good spray of gt85. I also lubed the cable guide under the bottom bracket.
I noticed the cable had a bit of a kink in it so I put a new cable in...still no joy.

While the cable was out I indexed the shifter and it was smooth, and got the chain of and manually moved the rear mech to its extremes, again, silky smooth. The limit screws are set correctly.

There doesnt seem to be a happy middle ground for up and down changes... any ideas?

 

[HLaB]

Have you cleaned and lubed the mech its self?

 

[potsy]

New outer cable?

 

[Peteaud]

New outer cable?

+1

Bet its worn away

 

[PaulSecteur]

Ok, new outes next.

Yeah, I had the rear mech off and cleaned it (it also had a spray of gt85) But it was smooth to start with, and just as smooth after.

EDIT: thinking back, when I sprayed gt85 down the cable outer from the shifter it was really dirty gunk that came out, with quite a few shards of metal in with it.

 

[accountantpete]

Chances are this is not the source of your problems but I had the same problem - eventually tracked down to the adjuster screw had snapped in half. It may be slightly related - make sure that the cable is snug at all points where it meets the adjusters.

 

[PaulSecteur]

eventually tracked down to the adjuster screw had snapped in half.

Do you mean the barrel adjuster in the rear mech?

(All cables are snug to the stops and dont move)

 

[cyberknight]

Assuing you have got clean cables and have tried squiting some lube into the shifter which can sometimes be a sticking point have you got the cable routing round the screw where the cable attatches to the rear mech right?
I installed a new rear mech a while back and got the cable the wrong side of the screw and it caused inconsistant shifting as the cable pull was slightly wrong.

 

[accountantpete]

Do you mean the barrel adjuster in the rear mech?

Yes - it snapped mid thread. Can't see it being your problem though.

 

[rusty bearing]

Cybernight has mentioned one of the two things its likely to be, the other is to replace the inner cable and either grease the old outers or replace them too, can of spray grease needed for this. Being able to get gears changing smoothly in one direction or the other but not both is almost always a classic sign of cable problems.

 

[Andy_R]

Ok, new outes next.

Yeah, I had the rear mech off and cleaned it (it also had a spray of gt85) But it was smooth to start with, and just as smooth after.

EDIT: thinking back, when I sprayed gt85 down the cable outer from the shifter it was really dirty gunk that came out, with quite a few shards of metal in with it.

There's your problem. New outers needed, as there will still be crud embedded in the plastic inner liners in there.

 

[PaulSecteur]

I will be popping down to decraplon and getting one of these to try...

http://www.decathlon.co.uk/derailleur-hose-id_8086073.html

 

[PaulSecteur]

I have just replaced the right side shift cable outers with those from the link above, and everything is back to being loverly and clickerty-snickerty.

1 click, 1 change up or down.

Many thanks all!!!

 

[potsy]

Makes such a difference having new cables, I got the tip off Globalti on a forum ride when my changing was getting a bit hit and miss, try to change them twice a year now

 

[Svendo]

I have DA 7900 which is notoriously finickety and sensitive to cable friction. The slightest bit of muck or kink in the outer or inner will affect the shifting. In the last six months I've been through one complete cable set, and a metre of on-its-own cable outer, but this is partly because I've had a run of crashes and each one has kinked the handelbar outers. I've also stripped a single thread from several cables rethreading them through ferrules, so another incidental tip is to remove ferrules from outers when rethreading cut cables, and then push them back onto the outer, even if you've superglued the cable!