[Closed] Whats causing the chain slack?

Chains too long - if you still have the old one, make sure the new one is the same length.

You shouldn't be using the small/small combination across the chain set, either...

It's the same length as the old chain though. Surely this is what your chain should look like at full stretch ?

http://tinypic.com/view.php?pic=2hz270j&s=9

I'd think if you want to cross chain like that, you'll need a longer cage derailleur.

I’d think if you want to cross chain like that, you’ll need a longer cage derailleur.

This. You shouldn't really be using the smaller sprockets with the smallest chainring. The small chainring is really only for winching yourself up steep stuff in the bottom three or four gears. As long as it's working properly across all the rear sprockets in the middle chainring and has enough chain to wrap around the big-big combination, it's fine.

I get what you are saying but the chain is so slack that it's literally sitting on the chainstay when in the smaller cogs and I do not think chain length is the issue as you can see from my photos. I just don't understand what's causing it!

To clarify, your using the same chain length as the original chain and that didn't have this slack in small/small?

yes

when running small to small or the first 3 smallest cogs to small my rear mech looks like this - https://photobucket.com/gallery/user/forbez/media/bWVkaWFJZDo5Nzk3MTI5OQ==/?ref=

The chain is rubbing on itself

My guess is it's always been like that you've just not noticed.

How about sticking the old chain back on just to check? Oh and has your old chain stretched to the extent where it is the same length as the new one but has fewer links (OK that might be daft but...).

What does it look like when you sit on the bike?

I recon you could loose another link out of that, but you need to take the shock off & see what suspension movement will do to it if you want to do it properly.

This. You shouldn’t really be using the smaller sprockets with the smallest chainring. The small chainring is really only for winching yourself up steep stuff in the bottom three or four gears. As long as it’s working properly across all the rear sprockets in the middle chainring and has enough chain to wrap around the big-big combination, it’s fine.

I disagree with this. My 2x9 bikes are set up so all gears can be used on each chainring ( bar small / small) so I have 9 high range gears and 8 low range gears. No issues whatever

From that pic is the mech not swinging back far enough? Is the main mech for and aft pivot seized?

Quiet bizarre this isn't it?

This might well me awake for a while tonight.

It's the bike equivalent of Brexit. A paradox inside a blank hole!😁

Is it me, the alcohol or lack of sleep, but does the main spring that I can just make out above the ferrule look like it’s still under tension even though the mech is as far back as it can come?

How has the cage rotated so far back - has the mech lost the pin that stops this (on Shimano mechs, anyway)?

My 2×9 bikes are set up so all gears can be used on each chainring

But that's a 3x9, from what I can see, and the OP's talking about small-small, isn't he?

I mean the pin he removes at 7mins20 in this video:

That could cause your symptoms. Doing a full stripdown and rebuild of a mech like that is a useful exercise, helps you understand how it works thus making it easier to diagnose problems.

I thought you didn’t set chain length that way on SRAM stuff - have a look at pages 19-22 here: TECHDOC

Looks different to your set up (big/big pic)

One of those jobs that you'll just have to do properly. Shock off, big to big and see how many (if any) links can be removed ensuring that you check it throughout the range of suspension travel.

There’s quite a bit of misinformation in this thread I think.

Crosschaining isn’t ideal and will be noisy/inefficient but won’t cause your chain to fall off unless something is badly wrong. Even if you ‘aren’t meant’ to use certain combos the setup should keep the chain on in any gear and any suspension position. If it doesn’t then the bike is a crash waiting to happen.

Derailleur cage lengths are set by the capacity requirement- ie, the amount of loose chain hanging off in the smallest-smallest combination that needs accommodating. Derailleur cages literally exist for this job. Capacity is determined with the usual tooth difference formula, compare the result against the derailleur mfr’s data chart and establish if the cage is the correct length. This is the only way to correctly determine derailleur length.

Chain sizing on a full sus bike needs to be done using the usual big-big-not-through-derailleur plus two full links method but as the back end doesn’t stay in one place you need to either remove the shock or deflate it and then eyeball the back end while moving it through its full travel. Once you’re sure you know where the back axle is furthest from the BB, tie the frame in that position so it isn’t going to move and then do your standard chain sizing.

Chains don’t actually stretch even though the word is used. The rollers get worn and the result is that the engagement becomes looser for a given tension (derailleur means this wouldn’t happen) and they don’t fit tight tolerances anymore so gear indexing doesn’t work quite and everything gets worn out rapidly by the out of tolerance component in the close tolerance system. Often leaving the ‘stretched’ chain with the original components will give acceptable life although you’ll have totally destroyed the drivetrain by the time anything needs replacement. A chain that has ‘stretched’ by enough to give anything like this would be an engineering marvel...

OP, assuming as you say the chain is the same length it always was (holding alongside is usually good enough but link counting is the ultimate) then I’d guess that the issue here is to do with the bike having sat unused several years. Either something to do with the RD is very wrong - possibly the derailleur spring isn’t as tight as it was or the backend is in the wrong place for some reason (probably shock related) are my first guesses. The cage having rotated for some reason could also be a good call.

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My 2×9 bikes are set up so all gears can be used on each chainring

But that’s a 3×9, from what I can see, and the OP’s talking about small-small, isn’t he?

both my 2x9 ( 3x9 minus the big chainring)and 2x10 bikes will run small / small quite happily. I have them deliberately set up like that because of the way I use the gears ie down to the small chainring on every climb but using a range of gears. I use the chainrings like a low and high range