Derailleur shifts gears by itself

Matthijs

Hi,

I don't know if I am in the right section for this question, I hope so.
I have had a brand new bicycle since this last Saturday 30 May. So far I have only done two 6k rides.

The bike has Shimano Acera 3x8 speed derailleurs.

Problem is that the chain goes back and forth between 3rd and 4th gear on the rear derailleur by itself. Right now the shifter says it's in 3rd, but when I look at the cassette, the chain is on another sprocket than that right now. It won't stay in either 3rd or 4th for longer than like a minute when riding. It does stay in all other gears.

I googled, and since the bike is new, it can't be dirt, wear or no lubrication.
So I guess I have to tune the rear derailleur? With the screws or is it the cable that needs adjustment?

Please help.
Thanks.

PS. I can't take it back to the store. The store is in Tipperary and I live in Dublin.

el tel

Sorry, thought this was abut the new Shimano fully automatic gear system, but realised it's not out yet

easygoing39

The bike's haunted.

fed up sick and tired

Matthijs wrote: »

Hi,

I don't know if I am in the right section for this question, I hope so.
I have had a brand new bicycle since this last Saturday 30 May. So far I have only done two 6k rides.

The bike has Shimano Acera 3x8 speed derailleurs.

Problem is that the chain goes back and forth between 3rd and 4th gear on the rear derailleur by itself. Right now the shifter says it's in 3rd, but when I look at the cassette, the chain is on another sprocket than that right now. It won't stay in either 3rd or 4th for longer than like a minute when riding. It does stay in all other gears.

I googled, and since the bike is new, it can't be dirt, wear or no lubrication.
So I guess I have to tune the rear derailleur? With the screws or is it the cable that needs adjustment?

Please help.
Thanks.

PS. I can't take it back to the store. The store is in Tipperary and I live in Dublin.

Personally, I would start from scratch and do it from the beginning. Which I did.

It's not difficult to do it yourself. I did it without having a clue previously just by using YouTube. Tons of instructional videos there.

Satisfaction from doing it yourself, and you will get to understand the principles of the systems for fine adjustment and future reference.

Can't believe the worthless nonsense of the two previous replies above.

connie_c

watch this video, explains it all, its fairly easy to fix

clipless

Hi. There is no need to go near the screws, the cable tension is all you will need to adjust. If the gear is going down from 3 to 4 that means the cable is too loose so turn the cable adjuster on the derailleur anti clockwise and vise versa if its going the other way. No more than one or two turns should be all you need. If you have a stand do the adjustment while you are turning the pedals so you can see what is happening.

Hope this helps.

The Gram

This isn't unusual in a new bike. Cables stretch a bit and the gears go out of tune.

It's one of the reasons bike shops offer a service at around 6 weeks.

I wouldn't think you need to go messing with the limit screws at this stage. For minor adjustments there is a cable tensioner right where the cable enters the derailleur. Give this a quarter turn and see if things are better or worse. If here getting better keep going until it's sorted. If things seem worse you're turning it the wrong way!

For larger adjustments, put the chain in the smallest cog. Loosen the nut holding the gear cable in place and pull it tight with a pliers. Then tighten the nut and run through the gears. If there is still some phantom shifting, adjust slightly using the cable tensioner as above.


....basically I'm repeating the four posts above!

iwillhtfu

You only have the bike a week it hasn't been set up right. It's unlikely the cables have stretched over such a short period.

Bring it back to the shop and get them to index the gears correctly. Don't start fiddling around with it you can do that when it needs to be serviced.

fed up sick and tired

iwillhtfu wrote: »

You only have the bike a week it hasn't been set up right. It's unlikely the cables have stretched over such a short period.

Bring it back to the shop and get them to index the gears correctly. Don't start fiddling around with it you can do that when it needs to be serviced.

A more careful reading of the OP by you would have revealed that it cannot easily be taken back to the shop.



Deal with the world as it is, not how you'd like it to be.

- Jack Welsh

Matthijs

Thanks for the replies.
Turning the cable tensioner anti-clockwise a bit seems to have improved the shifting.