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I have a Scott E-Genius 730 Plus mountain bike (around three years old). I had a chain snap recently, so I have replaced the rear 10-speed cassette, and am now trying to route a new chain correctly. I have removed a few links, as the chain comes with 116 links and I think I only need 112, and I've added a quick link.

However, I am struggling to visualise how to put the chain back on, and I'm tempted to think there is an issue with the dérailleur. I've seen the pictures in this question but I can't make head or tail of them.

Here is a general image of my bike taken from the internet. You can see that the chain travels from the top of the crank pinion, over the top of the cassette on the rear wheel, loops around the upper dérailleur cog on the right hand side, then loops around the lower pinion, before travelling back to the crank.

Shop picture of an E-Genius 730

A key thing here is that the centre of the cassette, and the two dérailleur cogs should roughly be on the same vertical line, as per the image. I have another MTB (a KTM Action Macina) also with Shimano gear components, and this confirms that there is an approximate vertical alignment between these three gear pieces:

KTM dérailleur with superimposed graphics

However, my Scott is not like that. The cassette and the top pinion seem to be in vertical alignment, but the arm movement of the dérailleur mechanism would currently have to rotate some 90° anticlockwise in order to produce the same shape. I appreciate the problematic unit is not under spring/chain tension, and good examples of correct working order are under tension, but that is not the issue - the dérailleur just won't go into that shape. I cannot apply any more hand force onto the bottom section (i.e. rotating the blue bar anticlockwise) without breaking it.

Scott dérailleur with superimposed graphics

Here is an image of the Scott gear system without the superimposed graphics:

Scott gears

I am 99% sure that the dérailleur is not bent and was not modified or adjusted since the chain snap, and it was working fine previously (other than clanking a lot, due to poor chain condition). Of course, this position means that the chain is too short, especially now I have taken some links out of it.

Has my dérailleur slipped into an incorrect position, or have I made an error with my chain routing that needs correcting? My Scott has a chain-bounce switch, but either position does not help rotate the bottom section to a near-vertical orientation.

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    Welcome to bicycles. The text is nice and clear, but the photos would be clearer in full colour and without the big red blobs on, might be worth editing back to normal
    – Swifty
    Jun 2, 2020 at 16:34
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    Yeah, I would swap them out. If someone knows about derailleurs enough to answer, they will know which way things should be. The words are descriptive to help too
    – Swifty
    Jun 2, 2020 at 16:40
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    Looks to me like the chain is too long.
    – Daniel R Hicks
    Jun 2, 2020 at 17:17
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    There are a dozen different ways to screw up mounting a derailer. Without being there and twisting the derailer around it's hard to guess what the particular problem is.
    – Daniel R Hicks
    Jun 2, 2020 at 17:43
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    The clutch mechanism would definitely be the first suspect. You do have it disengaged, right?
    – Argenti Apparatus
    Jun 2, 2020 at 19:00

2 Answers 2

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The solution turned out to be very simple - after the first 5° of sweep, if I push extremely hard, to the degree I feel a breakage is inevitable, another ~175° is indeed available. The amount of torque required to burst past this apparent stop is enough to make a 20kg e-bike creak against the maintenance stand clamp! Interestingly if the anti-slap clutch is off, the sweep is even harder to make, and there is almost a scratchy, harsh resistance to the movement. I thought the clutch was meant to make it harder when it is On, not when it is Off, but mine is the other way around.

During my investigations, I tried to remove the fascia plate to examine the clutch. There are three hex bolts, arranged in a triangle formation; I removed two, and managed to wear away the hex key slot for the third, and I may need now to drill that out. I have decided not to investigate this further.

Given my findings, I was finally able to replace chain - I used a bungee cord to keep the dérailleur forward, so the quick link could be fitted. However it feels like it may be worth replacing the dérailleur unit entirely - the chain is now clanking in a way that it did not before, and it is under far too much tension. I wonder if the chain snap caused the dérailleur to fly back so violently that it has broken the clutch.

The dérailleur has RD-M7000 stamped in the metal casing, but a cursory search suggests there isn't much support left for 10 speeds. I will have a hunt about to see what I can find that will fit.

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    Its not todays way to get girls into bed and impress the jocks, so you won't see it in trendy coffee table magazines, heaps of 10 Speed still used in the real world. Any decent sized shop will have 10 Speed parts on the shelf, otehrwise order in exactly what you want
    – mattnz
    Jun 2, 2020 at 20:29
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    10 speed SLX does seem to be less available but 10 speed XT or 10 speed Deore will drop in just fine and trickle down tech means a 2020 Deore will be better than a 2016 SLX.
    – Warren Burton
    Jun 2, 2020 at 21:18
  • Ah right, thanks @WarrenBurton - that's useful to know. I will have another look with wider search parameters.
    – halfer
    Jun 2, 2020 at 21:21
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    I'll roll with 10s XT (Model M786) all day. Use the m8020 front derailleur, which are dirt cheap, on my 2x10 (mixed generations play well together at the front drive only). @mattnz Most frequently heard comment from bike chicks on my set-up: "Ohh, XT, baby. That's hot!" Despite the age, it still rocks. Also, plenty of NOS, 10 speed, XTR parts (model #'s in the 900's) are available in the market at ok prices. Trickle down aside even tomorrow's Alivo will be hard pressed to perform like yesterday's XT or XTR, and it'll never have the "jena se qua," of the top dogs.
    – Jeff
    Jun 2, 2020 at 22:59
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    @Argenti: I take the view that discovering the dérailleur arm was extremely stiff (and not actually locked) is essentially my answer. The reason why it got like that may be less important than the fact the unit probably is in need of replacement. I made a somewhat wordy answer to offer trouble-shooting ideas to future readers who have a similar problem, but I'll gladly accept an edit if you wish to make one.
    – halfer
    Jun 3, 2020 at 14:48
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With the clutch engagement switch in the "off" position, the derailleur cage should move smoothly with the only resistance being from the cage spring. All indications are that your derailleur has failed (there's a good chance this is what caused your chain to break) and needs to be repaired or replaced. Pre-COVID, replacements for 10-speed XT RDs were not difficult to find. But failing that, Microshift's XLE 10-speed RD (RD-M625L) is a suitable Shimano compatible replacement. Arguably lower quality than XT, but it will get you riding again.

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