- Hope T Rex and XT RM clearance (Not! Arrrghhhh!)
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).
the angle looks good because it’s on a standPosted 3 years ago
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?Posted 3 years ago
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 142×12 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.Posted 3 years agorobinlaidlawMember
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.Posted 3 years ago
The Rad cage will help though as it allows less b-tension, or just file a touch off the corner of that arm.
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?)Posted 3 years ago
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.
back later, will try standard cassette next.Posted 3 years agoDoh1NutSubscriber
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)Posted 3 years ago
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 clarityPosted 3 years agoreggiegasketMember
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).
whereas on your setup the opposite it the case. The torx bolt is above the allen bolt:
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?Posted 3 years ago
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.Posted 3 years ago
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.Posted 3 years ago
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…Posted 3 years ago
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.Posted 3 years ago
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