Help diagnosing SLX issue

The main issue is the cain coming off of the jockey wheels and getting caught up in the cage

The problem is you have an SLX mech. They do that. Soon it will saw itself in half and you can warranty it.

EDIT: For clarity its a very common issue on SLX. What causes it vs Deore or XT I do not know, the usual outcome is the chain will saw the mech cage in half just above the lower jockey wheel.

I usually, in order, go: align mech hanger with tool, mech on and set high and low stops, chain on and set length, set indexing, set b-screw as per shimano or sram instructions.

So if you were to check all of this in order,  I would buy or borrow a mech hanger tool if you can. Also check chain/ cassette wear and if replacing those, also replace the jockey wheels if they are worn out. Also if the chain had jammed in the cage a bit, it will have splayed the cage out a bit. So you will need to bend it back a touch. This is easy though as the cage is very soft.

I had shifting issues recently with this. Turns out the cable pull was wrong - the pull to the pinch bolt needs to be anti-clockwise when it seems more logical to do it clockwise. Gears are now spot-on.

Son’s SLX  just did this. Ended up being the jockey wheels.

The problem is you have an SLX mech. They do that. Soon it will saw itself in half and you can warranty it.

EDIT: For clarity its a very common issue on SLX. What causes it vs Deore or XT I do not know, the usual outcome is the chain will saw the mech cage in half just above the lower jockey wheel.

This is actually the second mech I’ve had on this bike as the first one did exactly the same thing you describe, the cage just ate itself and snapped, I wasn’t previously having the same issues I’m having now so was most confusing at the time

So the SLX mech is just a bit…pants, then?!

just looking again, after cage jumps when back pedalling, the chain now wants to go to the smallest sprocket and the cage was getting caught on the largest 2 sprockets

@reeksy has new jockey wheels sorted it?

starting to wonder if new jockey wheels or new mech is the way forward?

@rascal like this or another way? (Bike is wheels up in the picture)

https://ibb.co/MnfSqNy

I've got SLX 12 speed long cage mechs on wto bikes and neither have this issue. Only issue I've had is with a sticky pivot.

  https://streamable.com/opabve

mostly noticeable when back pedalling on the two biggest cassette sprockets

Back pedaling in extreme gears is always going to cause problems because of the chainline.

First thing I would try is getting a hanger alignment tool and making sure the hanger is straight.

I spent ages fiddling around trying to get it to work, in a rush bought a new one and the wobbly wheels is the only difference. That’s fine, I have the body as a spare.

Ruling out a design fault with the mech itself. When I have had issues like this, it has been down to worn out jockey wheels. Unfortunately when a chain has come off several times like you say, the cage may well be damaged as well!

Back pedalling issues I've had have been freehub bearings dragging/knackered. The chain jumping/glitching on the cassette and/or jockey wheels was a stiff link/damaged chain!

This is where I would start.

Reading ben's post is strangely reassuring as that's exactly what mine is doing and i couldn't figure the cause as it's very random when it does it. Did it from new too

Was googling for a new plate over weekend before it inevitably is sawn through as it's getting very thin in one spot

How much side to side play is there on that top jockey without the chain? Has the cage taken even a minor hit and is already bent (they are cheese-like)?

And is the chainline OK on the top two sprockets?

I have an SLX mech, which is running fine. The only other thing to check might be that the jockey is running freely, I had one which squeaked from new in the top two sprockets (throughout the entire Jennride...) and found that it was rusty inside straight from the packet.

Ruling out a design fault with the mech itself.

I wouldn't rule that out - the problem is only seen on SLX mechs and can happen whatever the age of mech. While it's possible that there may be another contributing factor, the fact that it only happens on SLX mechs points to a design difference between SLX and the other mechs in the range as to why it rapidly becomes terminal.

@martinhutch difficult to say but guessing, I’d go with 2-3mm

mech hasn’t taken any knocks or impacts

jockey wheel is free moving and the chain line seems to be ok

I wouldn’t rule that out

Of course not. It's possible and wouldn't be the first time a particular mech was susceptible to premature failure with 1x wide range!

There is an amount of dried lube on the jockey wheels also, which obviously can’t be helping matters

in inclined to agree with @benpinnick as this will be the second one that has shown symptoms of not being great I’ve had

might give it a good strip down, clean up and new setup to see if that helps any but aware the cage will possibly go like the old one did at some point

Jockey wheels don’t look terribly worn so again, suspecting the mech design / known issue factor

Just in case, would any 12 speed deore / xt mech work with the current SLX shifter? Wondering if it’d be more prudent to change the mech as opposed to splashing out on new jockey wheels

Yes, any 12 speed shimano mech will be fine.

You could try some XT jockey wheels first, I guess, or just bending the cage in a fraction by hand as a last resort.

Never heard of this before, I have an SLX as an emergency spare still in it's box, I've also got a few spare nukeproof jockey wheels from the CRC sale, I was planning on changing jockeys anyway, funny how the usual sources haven't highlighted the issue.

Back pedaling in extreme gears is always going to cause problems because of the chainline.

This isn't true. It's a Shimano cassette problem. I've got 3 wheelsets I use between 2 bikes. I can't back pedal on the wheelset with a slx cassette without it dropping off the biggest cog. It's fine on the other 2 sram cassettes over both bikes. A friends bike with an entirely SLX drivetrain does the same.

Yet I can back pedal all day long on my full SLX tranny although I don't do it that much for obvious tractive reasons 😂.

Not much of a consensus on this.

This isn’t true. It’s a Shimano cassette problem. I’ve got 3 wheelsets I use between 2 bikes. I can’t back pedal on the wheelset with a slx cassette without it dropping off the biggest cog. It’s fine on the other 2 sram cassettes over both bikes.

Mech design choice probably, rather than a cassette thing. Don't SRAM have N/W jockeys, which presumably have benefits (and downsides)?

2x 12 speed Deore, chain doesn't fall back pedalling in the 51t cog, one is a 52mm chainline on 135mm frame. My SLX 11 speed falls off the 42t cog when back pedalling.

Cable routing should be

My SLX M7100 mech always seemed crap too. Shifts always seemed a bit off (with a aligned mech hanger), and chain came off the jockey wheels constantly. Eventually snapped around the top jockey axle, had probably only done about 100 miles.

I had this with a 12sp xt mech on a sunrace cassette, so I think it's most likely the chainline/mech design not cassette. Anyway, mech hanger realigned, cage bent straight again and new aftermarket jockey wheels fixed it.

Yeah, I did a straight swap for an X01 mech, same everything else, and all the problems went away.

I did get a warranty replacement SLX, which I was going to hang onto as a spare (I figured I might just have had a bad one), but given as mine doesn't seem to have been a unique experience, maybe I'll move it on.

I've got full 12sp SLX (XT shifter) on the Ragley and SLX cassette, mech, chain, XT shifter, Praxxis chainring on the ebike (against advice re: 12sp SLX on an eeb). 

Both work flawlessly - however the ebike wouldn't play at all at first. Swapped for a new hanger and perfect. Side by side, couldn't see any difference in the old vs new hangers.

Have spent the afternoon dismantling, cleaning, regreasing and setting back up, problem is still there but not as severe

in hindsight, bike has to go to the LBS for a brake bleed (tried it myself, cocked it up spectacularly) so might get them to check the hanger whilst it’s there

Thankyou for all the replies, folks, as always, STW hive mind has been a massive help

Quick thought if you say the cage is catching on the two largest sprockets, are you sure your b-screw adjustment is ok?
And is your chain too short?

Had a quick look and perhaps I spoke too soon. Is that what people mean when they say the cage is being sawn through?

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No thats bad bTension setting - the cage saws through just above the lower jockey wheel. The chain jumps off the wheel and runs on the side, one side of the chain gouging the cage as it goes.

Mine failed like this:

^ Thats the one, although this time on the upper jockey.

Had the OP's issue last year whilst riding up a climb at Afan.  Mech disintegraed.  Walked back down to shop at Glyncorrwg and fitted a Deore mech.

All has been well until weekend just gone when the chain starting coming off the top jockey.  Only happened on rocky descents and possibly when quickly changing down the gears.  Chain wasn't in the best condition so have cleaned and lubed it up.  Hoping that has helped.

I had this a number of times with the SLX M7100.

Found that SJS Cycles sell the inner plates & the Deore M5100 is just £3.99 and a direct replacement (Shimano Deore RD-M6100 Inner Plate - SGS Cage - Y3HK26000)  https://www.sjscycles.co.uk/gear-spares/shimano-deore-rdm6100-inner-plate-sgs-type-y3hk26000/?sessionid=2cd71395bc48d1be94a3a6f536e7fe25825e844f

Actually carry a spare inner cage & jockey screws when out for big/long days

It would then happen again really quickly, but swapping in the XT M8100 jockey wheels with bearings rather than bushings in the SLX ones seemed to cure the issue (Shimano Deore XT RD-M8100 Tension & Guide Pulley Set - Y3FW98010 @ £16.99)  https://www.sjscycles.co.uk/gear-spares/shimano-deore-xt-rdm8100-tension-guide-pulley-set-y3fw98010/?sessionid=2cd71395bc48d1be94a3a6f536e7fe25825e844f

YMMV

Thanks again, all

for that (those) price(s) I might take a punt on new cage (stock was nil when this happened with my previous derailleur hence buying another) and bearing jockey wheels to see what happens

Ive had those symtoms on two 12 spd slx mechs and both times it was a cracked cage. No probs since i changed to xt on one and ab aftermarket cage on the other

When I had a chain jumping off the side of the lower jockey wheel on my Deore, it was a worn jockey wheel.

With regard to it being SLX-specific, almost all the parts are the same as Deore, pretty much only the cage inner and outer plates are different.

So someone sufficiently motivated (like, say, Shimano) could assemble 3 Deore mechs, one with the left SLX plate, one with the right, and one with both. And see what happens.

Posted by: reeksy

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Son’s SLX  just did this. Ended up being the jockey wheels.

Yep, same for me.  And Shimano will not help you unless maybe after the chain eats through the cage when it jumps under load.  

From another Forum post: 

My SLX M7100 started doing this same thing, the chain would jump off the upper jockey wheel when pedaling through rough sections of trail. I had a local bike shop look at it and they couldn't find anything wrong so I asked about warranty. They sent it to Shimano service center (in France) and the warranty service was denied. When I got the derailleur back, I noticed the upper jockey wheel had a decent amount of side to side play. When I removed this jockey wheel, I found that the bushing was quite dirty and there was significant wear. The derailleur had maybe 300km (180mi) of riding on it, so it happened rather quickly--the rather open bushing system is not good for muddy locations. I replaced it with an XT sealed bearing jockey wheel and have not had the issue since.