I’m having a bit of trouble with my rear mech.

I can index the bottom 4 or 5 cogs, but then it starts skipping/autoshifting when I get to the top 4 or 5. However, if I work the other way and index the top 4 or 5, it starts skipping/autoshifting on the bottom 4 or 5!

Seems I can only get use out of half the cassette.

Groupset is used, but all used together. 1×9 speed/XT/LX. Chainline is centred on the middle cogs on the cassette.

Any ideas?

Bent mech ? or bent mech hanger ?

I did think that could be the culprit, but thought the shifting would have skipped across the full range? i.e. that I wouldn’t be able to get the 4 or 5 cogs indexed OK

Mech hanger out of wack. As you go up the block to the larger sprockets, the effect is amplified as the mech extends.

How old are the cable and outers?
Stiff cable release can cause those symptoms

Old cable and new outer.

I’m concerned it might be the hanger now, it’s on a Dialled Alpine so non replaceable.

A steel mech hangar should be OK to tweak back if done with a modicum of mechanical sympathy.

Take it to your LBS and ask them to check the hanger alignment with their special tool. Take the rear wheel as well.

Yup, it does sound quite a bit like a bent hanger. A bent hanger effectively changes the indexing ratio, so the mech moves a different distance per click.

Ben, given that you have far more than a “modicum of mechanical sympathy” and you are my LBS…is it something you could look at if I pop by? 🙂

How big a job is it to fix if it is bent?

Sure – I’m not at the shop regular hours this week, but I’ll be there most of tomorrow. 10-minute job if it is that 😉

bent chainring? I found that yesterday. gears were auto shifting on a couple of sprockets only, I noticed the middle chainting was bent and dragging the chain over on to the next sprocket, only on sprockets 4&5 though.

Great! I’ll give you a text 🙂

peter – sounds very much like mech hanger needing a tweak – I’ve had this a few times. easy to fix on a steel bike with the proper LBS alignment tool.

I had a similar sounding issue (tho only over the top 2/3 sprokets)

turned out the bearings in the hub were shot, and introduced a bit of play into the cassette which was just enough to let the chain slip down a sprocket when pedalling.

Give your wheel a tug back and forth in the direction of the axle, if there’s any more movement than almost none at all, then that might be something worth looking at.

Top jockey wheel worn ?

Probably Mech Hanger.

I know this sounds a bit dodgy. However, I have sorted this in the past without any alignment tools. Just taken the hanger off the bike, placed on solid flat surface, and hammer till flat. Sorted 🙂
Is this not the done thing?and if not why not?

Cheers
Ray

Removing the hanger from his frame would involve the use of a hacksaw…..
Secondly a re-bent hanger will be weakend from bending. By all means keep the straightened one as an emergency spare, but replace it with a new one just to be sure.

easy to fix on a steel bike with the proper LBS alignment tool

I’m guessing here, but is that an industry euphemism for “large hammer?”

Depends on the workshop – some use mole grips 😉

There is a proper tool for the job, it screws into the hanger and has a long arm with a pointer that lines up with the rim, so you can get the hanger parallel to the wheel.

take the hollow axle from an old wheel, this will thread into the mech hanger bolt hole

this then gives you…
a. something to align by eye (front/back, up/down)
b. something to grab hold of to aid realignment
c. something in the threads of the hold to prevent and mis-shaping

or buy a proper tool, one available from madison for £250

Presume you mean a threaded hub axle? I guess the correct orientation would be for the axle to be 90degrees to the dropout such that the axle is horizontal (assuming the frame is vertical)?

Im having a similar fight.

Running an SLX double I just replaced my cassette and chain.

On the workstand everything works perfectly and all gears are selected smoothly. But when I actually rde the bike there is a lot of chain slipping in the larger chainring and the smaller 3-4 cassette cogs. When using the smaller chainring everything works perfectly.

Any suggestions as to where to start?

Thanks

P

A proper tool only needs to cost £30-40, not £250 unless you are starting up a bike repair business. Even the Park DAG2 we use at work only cost £60-70 IIRC.
Tim

bigyinn, yeah, if there is an axle or wheel in the dropouts, you have a frame of reference.

(if that quote is high for the tool, apologies, its the first thing google threw at me [no DDG from work])

Park Tool DAG2 mech hanger alignment tool here £50 , prob one of the most used tools we have in the workshop, every bike that comes in for a service usually needs a hanger “tweak” of some sort.

penguinni, have a check of the hanger spring screw – the little screw that pushes against the knobble on the hanger. Tat controls how far around the sprocket the chain wraps. Maybe loosening it a bit will do the trick.

Changed a mates cassette on Friday. He’d also been having shifting problems the same as you are describing OP.

Turns out that the mech was bent, the spring in the cage was over stretched and floppy, and the mech hanger looked to be slightly out. I borrowed a Park DAG1 from my LBS. The hanger turned out to be properly bent. Put a new one in but that was still out. Ended up with the wheel out, a g-clamp on the hanger bolt so I didn’t strip the threads, and an BIG Bahco adjustable spanner on the frame to get it somewhere near straight. Minor adjustment with the DAG, a new rear mech, and it all shifts sweetly now.

So yes, probably a bent hanger. Only needs to be a bit out for it to have an effect.

Cyclus Hanger Tool on Wiggle. Don’t know how good it is.

Park DAG2 from CRC.

I had exactly the same problems on my most recent build. XT Shadow mech was the culprit – bent cage.

If it’s not the mech hanger, (or you fancy some garage / shed / man-cave time), check that the freehub is ok. I’ve had it before where the bearings inside have imploded and this was causing the free hub and therefore the cassette to ‘wobble’. Depending on which side of the cassette was loaded, depended upon whether or not it indexed correctly…

I use an old axle, and I stick a bit of threaded bar into the dropouts to give the best point of reference… Maybe the proper tool is slightly more exact but it won’t be by much. Depends how good your eye is I guess.

Really useful thing to be able to sort out at home, you’re lucky to have such a good LBS but I like to check mine from time to time and they’re always a little bit out just from everyday crashing.

Northwind.

That’s the advantage of building a relationship with your LBS.

It’s one of the tools I don’t have, along with BB & headset facing tools and headset fitting tools, but something that last Friday would have saved about an hour of faffing to get knowhere fast. Something to put on the Xmas list.