The rear arm of the RM (the bit the cable is attached to), is too close to the adapted cassette at points of the range, (specifically 28T -> 24T) the chain is touching it when trying to shift up so the shift is broken. (I can do a double shift then back if I have to).
It looks to me like pushing all the cogs outwards one level is simply compromising the clearance. It's nowt to do with set screws or the B screw, the TRex itself works fine as does shifting at each end of the cassette.
RM is M786. Cassette is a 11-36 (17T removed IIRC) with a Hope TRex (40t). Shifter is XTR. Hanger and frame are true.
what am I doing wrong?
No idea... I have same set up and it works fine. You using the longer b screw?
yes, the longer B screw fully wound in.
here's a pic showing the chain contacting the RM (this is after the shifter has been clicked for the upshift so the RM has moved, and is trying to reposition the chain but it's touching the RM back arm so is being prevented).
https://plus.google.com/photos/+MattGillam/albums/6037092664834972417?authkey=CL6aoozr05hA
the angle looks good because it's on a stand
(and yes I know the grass needs water, the cassette could be cleaner and the cable needs an end cap. when it works, I'll put one on!)
@matther01 good to know your set up works!
One up rad cage moves the jocky wheel back £20ish
Sure the mech is bolted on correctly and the b-screw doing its job correctly?
Bit curious about the frame, I suppose it's possible the mech/hanger position is doing something weird? There's more than enough clearance normally.
How sure are you everything's straight?
Best guess is that the arm is bent and/or twisted.
One up rad cage moves the jocky wheel back £20ish
Don't think jockey wheel is the problem, happy to be corrected. (see the pic).
Sure the mech is bolted on correctly and the b-screw doing its job correctly?
yeah think so
Bit curious about the frame, I suppose it's possible the mech/hanger position is doing something weird? There's more than enough clearance normally.How sure are you everything's straight?
it's a new frame, had the same issue on another frame (tho this is the first time I have diagnosed it fully).
frame rides straight, it's a 142x12 axle on sliding dropouts
Best guess is that the arm is bent and/or twisted.
RM is new, good theory but I don't think so. I'll look as it seems a good theory.
anyway ta for ideas, I ponder some more
If it happens in 2 frames and the mech is new I'm going to blame the mech. But, with the slidey dropouts, is the wheel axle moving in relation to the mech pivot, or are they all on the same slidey?
no, mech and axle are in the same sliderIf it happens in 2 frames and the mech is new I'm going to blame the mech. But, with the slidey dropouts, is the wheel axle moving in relation to the mech pivot, or are they all on the same slidey?
rad it
Do you need the b-tension screw as far in as that? As the mech body swings down away from the cassette, that arm will swing up toward it. If you can slacken the b-tension and get clean shifts you might be able to find the sweet spot.
The Rad cage will help though as it allows less b-tension, or just file a touch off the corner of that arm.
Is it a direct mount mech?
robin ta re logic of rad.I would have thought more B screw means more clearance, I'll experiment.
Stu the mech is http://www.chainreactioncycles.com/shimano-xt-m786-shadow-10-speed-rear-mech/rp-prod83162 (so yes. is that good or bad?)
Looking at this pic.
The direct mount mechs do seem to sit a bit further back.
That could be causing your problem?
[url= https://farm4.staticflickr.com/3816/13946283374_9172df0dea_z.jp g" target="_blank">https://farm4.staticflickr.com/3816/13946283374_9172df0dea_z.jp g"/> [/img][/url][url= https://flic.kr/p/nfomaC ]IMG_8754[/url] by [url= https://www.flickr.com/people// ]dRj0n[/url], on Flickr
What hub are you using? Are the end caps on the right way round if its a thru axle? That would cause the cassette to be too close to the mech.
hi - Hope Pro Evo 2 on a through axle. They are different lengths, wheel won't fit in the frame if adapters are switched.
I don't think it's the Trex causing it, I'd remove the Trex and try it without, does it still do it?.
I had this exact same problem last year, I think I later discovered my chain was too short and fitting a new chain the correct length sorted it
bunch of stuff to try there, will report back, thx for ideas
I had a chance to double check this morning.
Hope 40T with SLX GS RD in the same position as your photo has about 10mm clearance between arm and cassette/chain.
DP
I experimented with winding out the B-screw, there is a sweet spot where the 28->24 shift works, but it moves the problem elsewhere, specifically downshift from 3rd to 4th cog.
I uploaded pics of the set up in smallest cog, largest, and the rear arm of the RM, it doesn't look stressed or out of shape to my eye.
Chain is not excessively short.
https://plus.google.com/photos/+MattGillam/albums/6037092664834972417?authkey=CL6aoozr05hA
back later, will try standard cassette next.
I'd just file the inside of the mech arm until it clears the cassette
By removing the 17t you have moved all the bigger sprockets closer to the mech.
If you put a washer between your derailer and the frame this will regain some of the lost space.
Rear mech spacing relative to casette is also a function of the width of the dropout. There was a recent post here from Brant who said that SRAM were basing there rear mechs on 6mm dropouts so would not reach smallest sprocket if used on a 5mm dropout.
I bet that slider is steel - and probably slimmer than an alloy dropout.
(might have been 6mm and 7mm but you get the idea)
Does look like you have a very short hanger dimension, from axle centre to mech fixing hole centre.
Especially without an offset as the two holes are almost on the same vertical line.
Did you have this setup running okay before?
Have you double check the stops are meeting on the mech and hanger?
Has it just risen slightly as you have torqued the mech fixing bolt?
EDIT - For clarity
To me, it looks like the problem is the linkage between the mech hanger and the mech body is at the wrong angle.
If you look on this pic (from web) the mech hanger bolt (allen) is above the mech body bolt (torx).
[img] 
[/img]
whereas on your setup the opposite it the case. The torx bolt is above the allen bolt:
[img] 
[/img]
This isn't to do with the b-screw I don't think. It's to do with the linkage being at the wrong angle, which rotates the mech backwards. Maybe the mech hanger is putting the mech at the wrong angle?
Slightly different setup, obviously... But on my Titus FTMC with SRAM mech, the RM bolt is further rearwards of the axle.
I have a feeling you've discovered an issue with compatability between your frame/mech/T-rex.
Though the OP mentioned it happened with another frame too- is that also direct mount?
Is that a matching frame or a different frame OP?
What frame do you have now?
Is everyone using the longer b screw?
You don't necessarily need it for 40t.
Something looks wrong on your last pic:
[img] 
[/img]
Surely at some point, the main body of the mech should be more horizontal.
The jockey wheel is a million miles from the small cog!
Edit: reggiegasket's spotted something above. Definitely in the wrong place there.
Frames: both are Canfields, a Yelli Screamy and a Nimble 9.
I have a feeling you've discovered an issue with compatability between your frame/mech/T-rex.
Yes, wondering this. Perhaps it's a 'Canfield' issue, it's reasonable to assume common DNA in the designs. I'll ask them.
@alexsimon not entirely clear what you're pointing out, could you point me to a generic pic showing the difference you have in mind pls.
In the meantime, I'm going to put a regular 11-36 on and try that.
ah missed reggie's post, thx reggie I take a look at that too.
I think a combination of rotating the mech around based on reggiegasket's post and then loosening the B-tension screw will see it fixed.
Here's a drawing:
[img] 
[/img]
The only way to achieve that would be to remove some material from the hanger.
Or, presumably the company makes a non-direct-mount hanger for SRAM. And I've heard you can buy the wee knuckle to convert a direct mount mech to a normal one? But that's all pretty messy.
Difficult one, to me it looks like the direct-mount hanger is basically out of spec. But if it works fine on a normal drivetrain they can reasonably say it's fit for purpose.
Might be a stupid question, but if you unclamp the gear cable can you cycle the mech through the cassette without issue?
ie, move the mech up and down while pedalling, even if you're moving the mech into a position it wouldn't normally get into when using the shifter...
Northwind - That knuckle looks like the standard shimano part to me, is it DM?
OP - I remember reading that Canflied use a 135mm maxle for a 142mm hub, which I thought was a bit odd at the time, is the hanger also set further inboard than usual?
Best suggestion is to back the B screw right off, reset to give the absolute minimum clearance at the 40T sprocket with the cage in working position and without chain. Then try that.
Ah, maybe I'm getting confused with all the pics, I thought this was a direct mount mech?
Someone posted a DM pic but I don't think it was the OP.
Looking at what I believe is your post on another forum, I can't see that rotating the mech will solve the problem...
It appears that, to me, your mech is too far forward in relation to the wheel axle.
Breakthrough: a standard 11-36 works first time, out of the box. I didn't even have to adjust the cables or screws. Spot bollock on, click and go. I think this establishes my assembly is OK as are the components, it's probably a compatibility issue.
OP - I remember reading that Canflied use a 135mm maxle for a 142mm hub,
Correct.
which I thought was a bit odd at the time, is the hanger also set further inboard than usual?
Could be, though I was wondering if the variable in question was the vertical distance between the axle and the RM attachment.
I'll drop Canfield a mail and ask them. Watch this space.
@conan yes that's me I'm sure.
Best suggestion is to back the B screw right off, reset to give the absolute minimum clearance at the 40T sprocket with the cage in working position and without chain. Then try that.
I did that, it just moved the issue elsewhere.
Did you back B screw off all the way.
With a short hanger drop and a possible, inset hanger too, you may not need much tension at all.
Otherwise, good luck, I have to go to work now.
Did you back B screw off all the way.
Yup, right to the point where the shifts on and off the 40T were failing.
@alexsimon ta for pic, Skitch lives!
rotating the mech around based on reggiegasket's
how do I do that?
From your pictures it's not a direct mount mech then.
It is according to this http://www.chainreactioncycles.com/shimano-xt-m786-shadow-10-speed-rear-mech/rp-prod83162 /p>
it has RD-M786 stamped under the cable arm, so that's it.
Description's wrong. That's not direct mount.
People seem to be suggesting rotating it as I drew isn't possible.
And as you said 'how do I do that?', I now assume they're right.
I thought you could just loosen it and rotate it.
Description's wrong. That's not direct mount.
OK. Out of my depth on the tech here so will take your word for it.
The direct mount mech is the same as the mech you have but you remove the top link and bolt it direct to the hanger. 🙂
mattjg - Member
Description's wrong. That's not direct mount.
OK. Out of my depth on the tech here so will take your word for it.
SSStu's pic on page 1 is direct mount. Not much in it, but the direct mount mechs forego the b-knuckle that standard ones have.
ok, I think the terminology confusion is that the RM is Direct Mount compatible by removal of the knuckle.
But my sliders aren't I think so my set up is 'correct' for the components I have.
Would a longer outer gear cable push the back of the mech down and rotate the whole lot as per the pic with the arrow above?
Yep it does seem correct for a N9.
no. mech position is fixed at the point where it bolts into the hanger/slider. the cable is cut to fit that not vice versa.
(singlespeed rocks! but for now I need gears).
Like i said earlier i had the same problem when fitting a general lee to my old Canyon
[img] 
[/img]
When i fitted a new chain the problem went away, basically my chain length was much too short.
do you remember how many links you added?
No Mate, sadly not. i purchased a new chain. The General lee converter was also 42t So would be different to the T-rex
Definitely the b-link angle being wrong as Reggie suggested. Loosen the main mounting bolt and it should snap into position unless the b-link is damaged.
nay, it's mounted properly, the tab of the RM nestling on the tab of the dropout
Canfield say they have no experience of range extender cogs, so that's inconclusive I guess.
My money's on non-compatible, though I'll try again with a longer chain when I get time.
Anyway am up and running with an 11-36 fine, no biggie.
A oneup RAD cage uses less b screw tension rotating the mech forward to a more normal angle. The main aim of the RAD cage was to get better chain wrap on the smaller sprockets for shimano mechs by rotating the mech as has been suggested.
I've just installed the cage and it brought the b screw back out about 3 to 4mm, not quite as far as it was with just the 36 sprocket but it has helped bring the mech back to a more normal angle.
There is a gigantic thread on mtbr about oneup vs woolftooth where a few people have the same problem and the consensus was filing a bit off the mech arm but they haven't tried the new cage yet to see if it fixes the problem. I wouldn't be keen on filing myself though.
ps folks saying the second knuckle bolt should be below, not above, the first, I looked at a bunch of pics of installs on other frames, you're right that's how they look.
@conkers yeah maybe I'll try a RAD. I don't mind filing the mech if essential but first want to be sure it's not my goofage that's the issue. did you order your RAD from the US or is there a UK stockist?
They have a uk warehouse I ordered Monday afternoon and it was here by Wednesday morning.
Your mech needs to be a medium cage though. I had to wait another day to get a medium GS inner cage plate from petra cycles to convert my long cage slx.
ta - the jockey wheels on my mech are 80mm apart centre to centre, do you know if that's a medium?
Your in luck my rad cage is 80mm bolt to bolt the long cage is 95.
ta
pps for folks suggesting RM may be mounted incorrectly - looks right to me
[img] 
[/img]
Can you not just slide the dropouts back a bit (couple of mm)?
Ignore that ^ , dont know what I was thinking.
it took you an hour tho ... 😉
Could you file down the stop on the dropout to effectively give it more rotation? Its possibly cheaper to replace and less structural than filing the mech. Its probably ba*d hard and nigh on impossible to do too.
Ive got the same setup on my 5 but my problem has been unshipping the chain, ive just taken a couple of links out hope I havent changed the problem!
Hi folks,
picking up and old thread...
mattjg, did you ever get this resolved?
I've got the exact same issue with a Cannondale Jekyll (2011 era) and medium cage xt. New mech, new chain, cassette in good condition.
Chain fouls on mech arm in the 24t-28t region, mech looks like it's hanging at some ridiculous angle. Have tried wranging the b-tension in/out, doesnt help.
I've taken off the 40t for now and everything works fine with standard 11-36 cassette.
Did swapping in a RAD cage change anything? My next step was to either buy one and try it or to take a file to the mech arm?
Thanks in advance 🙂