[Closed] Another classic "I can't adjust my rear mech"

Bent mech hanger?

Possibly but I have no idea how to tell. The frame is new (Foxy Carbon) and I know they can be bent when new but it does look very straight - is there a tool to check alignment ?

Can the cage be bent ? The shifting was OK on the old frame, not great but OK (which perhaps indicated that there was already a problem, but then again I don't know)

When I try to adjust the limit screw on the big cog, I feel that perhaps the screw goes "limp" (not sure how to say this) before the cage has gone as far as it should go to allow the chain to go round on the cog properly. This would indicate some misalignment.

Could it be that the chain is too long or short ? (looks good to me on both extremes).

"is there a tool to check alignment ?"

There's hanger tools but there's cheaper ways- an oldschool rear cup-and-cone axle has the same thread, so you can thread that into the hanger and then put a straight edge of some sort (I use whatever random bit of threaded bar comes to hand but there's loads of ways to do it) through the axle holes, makes for a nice combined straightening lever and straightness gauge.

I do this literally every time I have a wheel out and a bike in the stand and more often than not it can benefit from a wee tweak.

After having a real pain setting up an 11 spd drive train a while ago, I'd go with checking the mech hanger too.

You can buy a tool to check or make one yourself.

Or.... take frame to a shop you trust to check alignment.

I now have an alignment tool I bought and must say it can save a lot of agro. If only to prove the mech hanger isn't the problem.

Though it was on mine.😳

After a recent minor crash I now find my GX Eagle shifting is causing problems.... Will be using tool to diagnose this problem too. In short,a tool well worth having or making.

100% misaligned rear mech hanger.

Yep, read the title and thought "probably mech hanger". Read the post and thought "definitely mech hanger".

Like Northwind, I find that even when things are fine, if you're in a position to tweak the mech hanger, you might as well. It can always be a little bit better than it is right now.

Have you set the b screw?

have you set the lower limit (you haven't said)?

Is the chain too long?

Have you got the chain on the right way? XT 11 speed should have the writing showing.

I was always taught that the correct adjustment on the high limit was to set it up initially so that it's trying to shift itself on the the 12t cog, and then back it off enough that it doesn't rattle too much (i.e. you're not looking to set it so that it's quiet, it'll do that over time anyway)

BTW, feel for you OP, that Foxy is starting to sound like an "epic" build...

I’d go with mech hanger. I gave up in the end with my mad ones bend in the wind class hanger and bought the park tool, it’s lovely.

Bent mech hanger or you have threaded the gear cable the wrong way round the clamp bolt on the mech .

Sounds like a bent rear mech hanger if it works at one end of the cassette but not the other (mech could also be bent but if it was working fine on another bike I would guess at the hanger)

11 speed only needs to be very slightly out of alignment to have issues, really need a tool. 8 speed you could just stick an allen key in the mech and bend it until it looked straight and it would probably be functional.

You should have set the chain length with the suspension at max chain growth.

I would get a gear hanger alignment tool, CRC do one for £30, money well spent. (obviously "better" options if you want to spend more money from Park, Abbey, EVT etc)

I’m going to suggest chainline

i understand that if you are in the 4th or 5th cog at the rear if you sight down the chain it should be dead straight on the front ring.

It might be you need to get some spacers on the front to tweek the chainring in a bit.

I only suggest it as I had something similar and some spacers sorted it

Buy another mech hanger, as ideally you want a spare anyway, try that. Doesn't really cost you anything then....

Buy another mech hanger, as ideally you want a spare anyway, try that. Doesn’t really cost you anything then….

Unfortunately new mech hangers often need aligned when fitted.

Thanks for all the advice - I have eventually (after 2 hours...) found a sweetspot where both ends shift - but the only way to achieve that is to set the B screw with a significant gap between jockey wheel and 42t cog, perhaps 15mm or so. Any less and the 10t is very noisy and the chain start slipping a bit out of the 42t on the ramps.

Will get the shop to check alignment of both cage and hanger. It's possible that the cage is slightly bent and worked on the old frame because of the tolerances were not quite as tight.

Chain line is 49mm which I believe is correct for that tranny.

Only fear is that it won't take much to push adjustment out again on the trail which I can't check as the new shock is being repaired, but that's another (hopefully soon to be resolved) side of the this "epic" (indeed nickc!)

Generally speaking perfect shifting at one end of the cassette and not the other is a symptom of a bent mech hanger.

Alignment tools can be had quite cheap, or as above, just screwing something like an old axle in and using it as a pointer will help. I did this years ago when straightening a steel integrated hanger which I had twisted until totally fubar. I actually found a cheap ploastic berol pen than I could screw in as it was just the right fit. I used this as pointer whilst 'persuading' the hanger back into line.

On a steel frame with a badly bent integrated hanger, you also need an axle in the dropout so you don't close the dropout whilst 'persuading'.

I reckon the hanger is bent 🙂

Unfortunately new mech hangers often need aligned when fitted.

On a carbon frame? I've never had to do that, only ever had 2 carbon frames mind!

I am not sure what the fact that it's a carbon frame changes. The hanger is bolt-on aluminium.

It looks VERY straight if it's bent... The shop will have a look when they get my shock back, hopefully before Xmas.

Just an idea, is the spacing the same on an 11spd Sram cassette as on an 11 spd Shimano cassette? I know one of them has a small spacer to fit on the free hub body inboard of the cassette, and Sram use XD driver free hubs but don't know if there might be a slight difference in spacing.

Might be completely wrong mind.

Just an idea, is the spacing the same on an 11spd Sram cassette as on an 11 spd Shimano cassette? I know one of them has a small spacer to fit on the free hub body inboard of the cassette, and Sram use XD driver free hubs but don’t know if there might be a slight difference in spacing

Spacing between cogs is identical, their initial position on the hub is a little different, but that can be resolved by setting the H & L screws correctly.

I swapped forma  SLX M7000 11-42 on a SLX hubbed wheel to a SRAM 10-42 cassette on a DT Swiss 240 xD hubbed wheel, still using the M8000 rear mech and all I had to do was adjust the H & L screws accordingly.

Shifts perfectly up and down

Could be the..

sheep clangers?

It's true though, I've often found that with new frames, the sheep clanger is out of alignment, or sometimes missing altogether.

One other idea... I was having a mare setting up a Zee mech on my daughters new frame a while back. Turned out the mech hanger was a direct mount or something (Cube) and I had to remove an extra section from the mech. Once removed the shifting was perfect.

IME (FWIW) most of these sorts of shifting issues are cable tension based, rather than hanger misalignment, especially on brand new frames.

My workthrough

1. set H screw, slightly high on 11/10t cog,

2. wind in the cable tensioner on the shifter all the way, and then give yourself a complete turn to play with

3. set tension, make sure it's going through the mech properly

4 shift two cogs, if it won't go to the 2nd one, a 1/4 turn of the cable tensioner at a time until it does

5. shift up and down making sure it all goes pretty well, remember to turn the cranks pretty fast

6. now shift up to the lowest cog, if it won't, turn the L tension out until it does, if it still won't, then you not got all the cable released, and you need to go back to 3 and start over

7. set the L screw, then the b screw.

sorry if that's teaching you to suck eggs, but once you're trying to sort it out, it's easy to start turning screws this way and that...

Unfortunately new mech hangers often need aligned when fitted.

On a carbon frame? I’ve never had to do that, only ever had 2 carbon frames mind!

Yup, all the time. (I do this every day so see a lot of bikes/mech hangers) If you have a well finished frame and mech hanger in good condition then everything should be ok, however it often is not. So as a business if I fit a hanger I check the alignment and often find they are out, also means it can be eliminated as a potential issue.

Basic gear tune check;

Check;

no hub play

no excessive freehub play

cassette tight

wheel in straight/tight

mech hanger tight

mech hanger straight

mech tight

mech looks straight/no excessive play

jockey wheel play

Cables seated ok

Chain ok

Chain length correct

Cassette ok

H limit

cable tension

L limit

B tension

Cable return ok

Thanks nick, will go through your work flow.

If it was a SRAM mech, I would be guessing wobbly pivots. IME they last less time than a chain quite often.

So don't get eagle. Get the alignment sorted, check the other things, follow the guidance in the Shimano technical documents to get the cable tension correct.

Cheers - I am investigating if I should go direct mount too but difficult to tell.

Another avenue : I can see the markings on the chain so I know that's correct but could I have fitted in inside out ?

I mean rolled the other way around the cogs, would that make a difference on a 50% worn chain ?

I have a spare new SRAM 11-speed chain so I could just fit that for a laugh.

Speaking about SRAM 11 and 12speed derailleurs the gap between the biggest cog and the jockey wheel needs to be 15mm.

RD-M8000 is 5-6mm for 42t and 8-9mm for 46t (tip-tip)

Chain is big-big + 2 links with rear wheel at the furthest position from the bb (normally suspension bottomed out) for single double or triple.

On a carbon frame? I’ve never had to do that, only ever had 2 carbon frames mind!

From experience pretty much every new bike out of the box that we PDi needs an alignment tweak. Material the frame is constructed from is no factor, neither is RRP

Cheers – I am investigating if I should go direct mount too but difficult to tell.

generally and roughly speaking, direct mount hangers are quite a long way (2-3 cm) back from the axle centre, while conventional ones are somewhere near directly below the axle (cm or so behind the line)

err, I think.  I bet there's a shimano standard spec published somewhere

generally and roughly speaking, direct mount hangers are quite a long way (2-3 cm) back from the axle centre, while conventional ones are somewhere near directly below the axle (cm or so behind the line)

Yup

Just to update. The shifting issue was due to insufficient torque in the mech bolt into the hanger and ensuing movement. 10nm as per Shimano guidelines and loctite fixed that although I will need a long lever to remove the mech.

10nM? Wow, I don't think I've ever had one that tight/

But rocketdog said it was 100% mech hanger..

who to believe? 🤔?

So that’ll be a bent hanger be a bent hanger next time then 😉

Some mech hangars are Shimano/SRAM specific ....

I know my T-130 has 2 versions ... quite what the wrong version does I don't know.

10nm is as per Shimano's instructions although I suppose it depends on the hanger"s ability to take it too.

It's shifting great so not touching it anymore.