Gears sometimes not changing at the back

[marinbearvalley]

marin bear valley 27 speed Shimano.

Sometimes when in first gear (fastest) changing to another cog at the back does not work. I can feel the cable getting loose but the mechanism does not release. Only happens when in the fastest front cog. If I change the front cog then the rear gears start to work again immediately. Only happens occasionally. (Sorry about lack of terminology!)

I think the cable is pretty well adjusted although it does sometimes jump up or down a gear, again at the back.

Just wondering if this is a quick easy fix. Otherwise I will put in for a service and mention it when I get the rear wheel sorted. (see other thread)

 

[2Loose]

Does the lever click as it should when it fails to change?
If so, then it sounds like it may be dirty cables & outers - you could try flushing it through with wd40\gt85 or similiar to try and clean the crap out.

 

[marinbearvalley]

Does the lever click as it should when it fails to change?
If so, then it sounds like it may be dirty cables & outers - you could try flushing it through with wd40\gt85 or similiar to try and clean the crap out.

Yes they click and I can feel the cable getting slack. Have given everything a good clean/oil but it seems to be getting progressively worse. (i.e. more frequent) Must be something sticking but difficult, with being intermittent.

P.S. Thanks for the replies.

 

[kevin_cambs_uk]

I had a similar thing, and decided that the cable must have stretched after being on there for 9 years,
fitted a new cable on Sunday and its sooooo much better !

 

[Globalti]

Your cable outer has worn where it curves round to the rear derailleur, you ought to replace the outer every six months especially on an MTB used in dirty conditions.

Change the outer at least and all the cables at best; you'll be amazed at the difference it makes.

 

[marinbearvalley]

A new cable (inner and outer) hasn't made any difference. There seems to be something wrong with the way the derailleur takes up the slack in the chain. The part where it attaches to the frame - should that easily be rotatable by hand? When it gets jammed, if I start to rotate that part then the gears work again. It currently isn't moving when changing gears either? Something is not right there but I don't know what to look for??

 

[subaqua]

A new cable (inner and outer) hasn't made any difference. There seems to be something wrong with the way the derailleur takes up the slack in the chain. The part where it attaches to the frame - should that easily be rotatable by hand? When it gets jammed, if I start to rotate that part then the gears work again. It currently isn't moving when changing gears either? Something is not right there but I don't know what to look for??

yes, it should be quite free. try undoing the fixing cleaning the pivot and refitting.

you may need to re- index the gears afterwards. bike tutor has a good guide.

what model shimano stuff??

 

[marinbearvalley]

what model shimano stuff??

Deore. Or do you need more info.

I don't to play with the "b-screw" do I to fix this. Never really understood that.

 

[marinbearvalley]

One other possibly related question. I have the bike upside down. I have the smallest front cog. When in the smaller 2 rear cogs, the chain is rubbing against itself as it goes back around the innermost cog on the derailleur. Is this how it should be? (I do understand that these gears should not normally be used)

 

[marinbearvalley]

yes, it should be quite free. try undoing the fixing cleaning the pivot and refitting.

Have done this and it seems to working properly now. Although it is intermittent out on the road. I assume that fixing bolt should be tight?

 

[subaqua]

Yes fixing bolt should be tight.

http://techdocs.shimano.com/techdocs/index.jsp

is a good start point for set up info

http://techdocs.shimano.com/techdoc...DER<>folder_id=2534374302051135&bmUID=iWgzBos

is the deore specific section. the model no of the derailleur is on the underside of it.