Problems with new drivetrain

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autolycus

Über Member
Location
Surrey
I've recently replaced a 48/34 compact front chainset with a 50/34. This also entailed an ISIS to GXP bottom bracket swap. I was advised also to lengthen the cables (I have a high-rise stem) which i did.

All seemed to go well until i tried to index the gears. I cannot get onto the lowest (biggest) cog on the cassette when i'm on the large chainwheel. That's not exactly true - it will do it very occasionally on its own, or if i force it in by pushing the rear derailleur to 'help'. I've fiddled with the L screw B screw and adjusted anything i can think of, but it just doesn't want to know. The rear mech looks fine and i didn't have a problem with the derailleur before the changes.

Can anyone work out what's going wrong here, please?

Thanks.
 

Milkfloat

An Peanut
Location
Midlands
Firstly I would ask why you would want to cross chain so much - it is not generally a good idea. However, saying that. When it is not going in, what happens if you pull the cable a bit tighter by hand - can you make it go in then?
 
OP
OP
autolycus

autolycus

Über Member
Location
Surrey
Hi - thanks for replying. I don't particularly want to use the big/big combination, it's just that i've never been unable to do it before when indexing any set up, and none of the various instructional videos shows a problem changing all the way up and down. So i assumed there must be a problem with mine.

I cannot force the chain on to the big cog by pulling on the cable, only by almost bending the rear derailleur inwards by brute force, which is obviously not something i should be doing! Just using the shifter gives me a horrible rumbling as it tries to change down.

I was wondering if i need a longer chain, but i already have a 116 links (36t big cog)
 

Spiderweb

Not So Special One
Location
North Yorkshire
If you can push the derailleur cage towards the wheel and it shifts to the big cog then the issue is not the limit screw. It sounds like you need more cable tension so look at the derailleur from the back of the bike, there will be a barrel adjuster where the cable enters the derailleur, turn it anti clockwise half a turn, see if that helps. If not turn another half a turn.
If it shifts onto the big cassette cog only when you are on the smaller front cog then it may be that you need a longer chain.
 
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lpretro1

Guest
or you may have exceeded the capacity of the rear derailleur - if u only have short cage and are running a 50t with say a 32 it may give problems
 

Spiderweb

Not So Special One
Location
North Yorkshire
or you may have exceeded the capacity of the rear derailleur - if u only have short cage and are running a 50t with say a 32 it may give problems
I'm not sure it would make a difference as the OP hasn't changed the cassette for a bigger one and it was working before he changed the front crankset.
 

Ajax Bay

Guru
Location
East Devon
I think the RD is doing you a service. Why would you ever want to go large to large, especially if the large sprocket is a 36t(!)? The length of your chain sounds fine (58") (assuming 'normal' chainstay length) and I assume you fitted this for 48 plus 36 plus a (double) link). If everything else is OK then crack on and ride.
Picture of chain on large chainwheel and second biggest sprocket please or answer @Yellow Saddle 's question (looking from the side, not from behind).
 
OP
OP
autolycus

autolycus

Über Member
Location
Surrey
Thanks for all the feedback.

@Spiderweb: no adjuster on RD but anti-clockwise adjustment on shifter doesn't help - even going as far as raising a whole cog above what it should be.
@Yellow Saddle & Ajax Bay: the original chainset was 48/34 and the 11/36 cassette is original spec as is (i assume) 116 link chain (Sirrus Comp 2012). In any event, i did not lengthen the chain.

Here's a pic which i hope will address your question.
RD1.jpg
 

Spiderweb

Not So Special One
Location
North Yorkshire
Thanks for all the feedback.

@Spiderweb: no adjuster on RD but anti-clockwise adjustment on shifter doesn't help - even going as far as raising a whole cog above what it should be.
@Yellow Saddle & Ajax Bay: the original chainset was 48/34 and the 11/36 cassette is original spec as is (i assume) 116 link chain (Sirrus Comp 2012). In any event, i did not lengthen the chain.

Here's a pic which i hope will address your question. View attachment 130478
I think you need a longer chain, the extra 2 teeth on the crank has probably made a chain that was short but workable in the first place to unworkable.

Does it shift to the 36T cog at the back when you are in the small cog at the front?
 
Location
Loch side.
Thanks for all the feedback.

@Spiderweb: no adjuster on RD but anti-clockwise adjustment on shifter doesn't help - even going as far as raising a whole cog above what it should be.
@Yellow Saddle & Ajax Bay: the original chainset was 48/34 and the 11/36 cassette is original spec as is (i assume) 116 link chain (Sirrus Comp 2012). In any event, i did not lengthen the chain.

Here's a pic which i hope will address your question. View attachment 130478
Thanks for the pic, that puts it in perspective.

Your chain is too short. The maximum the RD cage should bend forward is 45 degrees and yours is at the limit with another sprocket to go. Start by putting one link onto the chain and then trying. There are only two possibilities that could still prevent it from going up once you've fixed the chain which should be fixed in anyway, it is too short. These two possibilities are:

1) The upper limit screw needs to come out a 1/4 turn.
2) The cable does not pull enough, which is a barrel adjustment issue that requires a complete cable set-up from scratch. In other words, loosen the cable anchor and start tuning the gears from top (small sprocket) up.

Let us know how it went.
 
OP
OP
autolycus

autolycus

Über Member
Location
Surrey
Thanks again to all. I'll get a longer chain to start with. It doesn't seem that 117 links is too common. I guess maybe118 links and perhaps remove one, but a quick look suggests this might be a problem as they all seem to be for 11speed. Any ideas?
 

Ajax Bay

Guru
Location
East Devon
Number of links has to be even so 117 links isn't just not common, it's non-existent. Your image shows a 58" chain on the 32 at present so an extra two links (ie to 59") will not do it (ie when it's on the 36t) - the cage will still be too far from vertical; I reckon you'll need 60" (120). But work out what length you need from first principles rather than just adding a few links. To get the long chain you need, best way is to buy your new chain from your LBS, explain the issue and ask that they find a few spare links (from the chains they've had to shorten) and a spare 'quicklink' / 'powerlink'. What's the RD? Assume its capacity is up to it (16 + 24?).
 
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