Odd shifting problem.

[cyberknight]

I am having an intermitent shifting problem that is driving me up the wall

About 30 % of the time when i shift into the small chainring the rear gears start jumping as if it wants to change to another gear , a slight push to the left on the rear shifter settles it down.I have checked chain wear and its less than 75 % just in case, the front chainring is worn but not hooked .

The bike is maybe 3 years old and had a new rear mech in the last year although i have fiddled with the indexing it is never crisp through the whole range so i was wondering if the cable needs replacing but i am unsure as i would have thought that cable tension would not change as the spring takes up the slack?

 

[djb1971]

Sticky cables or adjustment screws on the rear mech?

 

[cyberknight]

Sticky cables or adjustment screws on the rear mech?

I doubt its the screws as i have not changed them since i put a new chain/cassette on at the start of the year and the problem has just started , it feels like the rear mech cannot take the slack up quick enough .

 

[djb1971]

I'd try flushing the outer cables with some gt85 and cleaning the inners to see if it helps first.

 

[accountantpete]

Have you checked your chainline - it should be approx 41mm from centre of seat tube to the small ring (road double).

 

[cyberknight]

Have you checked your chainline - it should be approx 41mm from centre of seat tube to the small ring (road double).

only just started happening and never had any problems with it in 3 years but thanks .

 

[potsy]

I'd stick a new inner and outer cable on it, cheap and easy fix hopefully

 

[RecordAceFromNew]

I am having an intermitent shifting problem that is driving me up the wall

About 30 % of the time when i shift into the small chainring the rear gears start jumping as if it wants to change to another gear , a slight push to the left on the rear shifter settles it down.I have checked chain wear and its less than 75 % just in case, the front chainring is worn but not hooked .

The bike is maybe 3 years old and had a new rear mech in the last year although i have fiddled with the indexing it is never crisp through the whole range so i was wondering if the cable needs replacing but i am unsure as i would have thought that cable tension would not change as the spring takes up the slack?

Assuming your cabling is good/clean/not sticky, and given shifters rarely go wrong, if I were you I would prop the rear end of the bike up, vertical, and look from behind to check the mech/hanger is vertical and straight not having hit something. Then see whether the rear mech's top jockey wheel lines up accurately to each of the rear sprocket as you shift through them.

If they are all out by the same amount, you need to adjust the cable tension. Correct for one will correct for all.

If some are lined up and others are not, assuming you have speed matching shifter/mech you might have clamped the cable wrong on the rear mech. Not an uncommon issue since it is easy to do. The correct way to clamp the cable can be found in Shimano pdf of the rear mech.

As I said that is assuming your cabling is good and clean.

Regarding the odd front shift phenomenon, see whether it is still there after the rear shifts are ship shaped. If the problem is still there come back!

 

[fossyant]

Cables, cables.

 

[Globalti]

Change that outer cable at the derailleur, you'll be amazed at the deterioration in performance that you've come to accept as normal. I change mine every six months to keep the gears working crisply.

 

[cyberknight]

Cheers !!
Kind of confirmed my suspicions , i will be down the LBS asap and get a new cable.

 

[PaulSecteur]

I had a similar thing, on a newish bike. I took the inners out and they were rusted, and when I squirted some gt85 down theinners a fair bit of swarf came out. I replaced both with basic shimanoparts from decathlon, cost about a tenner

If possibe (and what i will do next time) is get the dura ace outers and ptfe coated inners (I think accountant pete was selling some a while back?) The dura ace outers are labelled something llike SP41, and the inners must have PTFE on the packaging... or get the equivelent from another brand.

Once both were swpped normal snickerty gear change were the norm again. Electronic shifting... PAH!!! (untill I can afford it!!!)

 

[cyberknight]

I had a similar thing, on a newish bike. I took the inners out and they were rusted, and when I squirted some gt85 down theinners a fair bit of swarf came out. I replaced both with basic shimanoparts from decathlon, cost about a tenner

If possibe (and what i will do next time) is get the dura ace outers and ptfe coated inners (I think accountant pete was selling some a while back?) The dura ace outers are labelled something llike SP41, and the inners must have PTFE on the packaging... or get the equivelent from another brand.

Once both were swpped normal snickerty gear change were the norm again. Electronic shifting... PAH!!! (untill I can afford it!!!)

£10 ?
Rich guy :0
since i saw you at the sportive the wife has had to go back to work , i am waiting till pay day for a big spend like that !

 

[cyberknight]

Replaced the cable yesterday and reset the mech so i will give it a run tomorrow and see how we go.
The cable did not look rusted but its worth changing for £2.50, did the gt 85 trick with the outers as well before i stuck the cable through.

 

[screenman]

Why did my brain miss the F out on the title of this topic.