Why does my Shimano Deore SLX dérailleur not rotate into the expected (vertical) position?

Question

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.

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:

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.

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

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.

halfer · Answer

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.

Kopsis · Answer

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.

Answered by Kopsis on July 24, 2021

Why does my Shimano Deore SLX dérailleur not rotate into the expected (vertical) position?

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