Weird shifting problem

[GrubNut]

I've got a problem with my rear shifting that I haven't been able to solve. One day the bike just started misshifting, skipping, riding up on the ramps, and dropping or gaining a gear. No matter how I adjusted the cable just couldn't get rid of the problem.

Happens intermittently.

I adjust the hanger. No fix. Replaced the hanger. Nope.

So I replaced the derailleur thinking it looked a little skewed and there's play in the linkages.

Guess what. $120 later problem persists.

What seems to be happening is that it is shifting too much. On the inner cogs the cable is too tight and the outer cogs the cable is too loose. So its tending to shift down on lower gears and shift up on higher gears. Weird.

So all that's left to replace is the shifter.

Anyone seen this behaviour with a worn shifter?

It's a Sram x9 grip shift. And yes the cables and outers is replaced and lubed (well I use graphite for cables.)

Any ideas?

 

[rone]

I've seen this happen on an XT rear derailleur when the cable was routed on the wrong side of the cable securing bolt, subtly altering the pull ratio.

Worth double checking?

 

[Registered Nutcase]

could the chain be to short?

 

[peril 787b]

How old is your cassette and chain? The symptoms you explain are almost exactly what one of my rigs is doing.
New cassette and chain and no longer ghost shifting/skipping or anything.
It's quite surprising how long cassettes don't last

 

[shakes]

Cheapest to most expensive...

First 2 guesses. Cable routing, and or sticky cabling. Just use triflow or similar to lube it Your shifter may also be gummed up, try blow it out with a compressor or similar.

2nd guess is hanger alignment. I know you've replaced it, doesn't mean the hanger is straight. LBS should have a jig style tool and about $25

3rd guess is chain stretch/worn rings. Look at your rings, if they are no longer nice and square and look more like your stereo-type shark fin... again your LBS will have a chain tension device and any mechanical staff will be able to spot wear straight away.

usually it's a combination of all three.

 

[0psi]

There is also the possibility that the drop outs aren't aligned. A decent shop should have drop out alignment gauges and hanger alignment gauges. As for gummy shifters, disc brake cleaner works a treat, squirt a bit in there blow out the excess and use a bit of spray lube in there.

 

[GrubNut]

Yeah I've tried all of the above and aligned the hanger etc, all gears and chain are fresh.

The thing is that the behaviour is the opposite to what you expect with any stickiness in the system.

It is shifting too far.

It is as if the cable is trying to down-shift in the lower gears and trying to up-shift in the higher gears. Like the actuation ratio is messed up and the shifter is pulling too much cable.

 

[BM Epic]

Yeah I've tried all of the above and aligned the hanger etc, all gears and chain are fresh.

The thing is that the behaviour is the opposite to what you expect with any stickiness in the system.

It is shifting too far.

It is as if the cable is trying to down-shift in the lower gears and trying to up-shift in the higher gears. Like the actuation ratio is messed up and the shifter is pulling too much cable.

Absolutely get a new cable, sounds dirty or stretched, but cable for sure!

 

[GrubNut]

Absolutely get a new cable, sounds dirty or stretched, but cable for sure!

I have replaced everything except the shifter. Chain cassette and chainrings are fresh.

The symptom is the opposite of what you would see if it was a sticky cable.

 

[T-Rex]

A couple of other possibilities, not already suggested:

1. How are the bearings in your hub? Play in the bearings can result in weird shifting behaviour.

2. Is it a dually? If so have you checked your cable routing for any tension being applied to the housing as the suspension moves? Or the steering? My DH bike currently has this problem, it changes gears with a bit of right hand lock applied to the steering.

3. Are all the cogs on the casette straight? It's not uncommon to bend a tooth on a cassette, and this can lead to the chain catching.

4. Is the derailleur (as distinct from the hangar) straight? eg has the cage or body taken a hit?

5. A really dumb one (I've done it....), do you have a 8 speed shifter and a 9 speed cassette, or vice versa?

 

[GrubNut]

Good ideas I'll check out the hub and freewheel bearings, and double check routing.

 

[MARKL]

I had a similar problem recently and somebody suggested a stiff link in the chain after I had gone through a similar process to you.

As soon as I looked at the chain I realised I had put the joining link in the wrong way (Wipperman link).

I imagine you could also get a similar problem with either a stiff link or link not joined properly

 

[0psi]

And please do let us know the outcome, the suspense is killing me. I'd have thought it would have definately been hanger alignment but seeing as it's not it's worse than an M. Night Shyamalan movie.

 

[BM Epic]

T-Rex has some good options, also try and see if your hanger is loose, this has happened to me and caused a lot of weirdness until i accidentally found the problem!

 

[T-Rex]

MARKL's comment just made me think of another possibility. Check for a twist in the chain, ie make sure all the plates on the links are perfectly flat. The easiest way to do this is to remove the chain and lie it on a flat surface eg the dining room table when your missus/mum isn't around.

And let us know the outcome.

 

[safire]

I had a similar problem a while back with the bike doing a lot of its own random shifting. Turned out that I had a crack in the bolt that joins the hanger to the frame. Took the hanger off to investigate and all looked ok but when I put it back on it felt a bit weird as I tightened the bolt (and I was by no means heavy handed!). Undid it again and saw the crack - smallest amount of pressure and the bolt broke in 2. New bolt and no more shifting problems.

As you have already replaced the hanger you may have eliminated this...

 

[mhuth1]

Maybe check your limiting screws????? if you have them to loose or to tight your derailleur wont like the top gear or bottom gear.

Depending what chain you have is it on the right way, some chains have a direction of pull and a top/bottom.

check you haven't kinked your cable while putting it in.

make sure your not using stupid combination's of gears such as first in the rear but big ring at the front.

check your wheel is in the drop outs straight.

check correct chain tension.

make sure exerting pressure on the grip shifter when riding as this will caise it to slip gears, like if your leaning over the back of the bike you will pulling slightly on the grip shifter wanting it to change up/down.

Failing ALL that take it to your lbs or buy some shimano gear

 

[nexusfish]

your not running a shimano derailur with those sram shifters are you? it will throw the gears out big time due to different actuation rates.

 

[harmonix1234]

Ah yes ^^^ The old sramano mash up could be it.

If the cable inside the shifter is not threaded properly you may have it pulling too much, or not enough cable and screwing with the actuation ratio.
I'd be pulling the shifter apart, cleaning really well and double checking that the cable is routed just as it should be. However, I have no idea how to do that as I have never used twist shifters. But I am assuming they are serviceable (?) (Correct me if I'm wrong).

Also, is it ghost changing gears when coasting, when back pedalling, when load is applied, or only when spinning the grip shifter?
Knowing WHEN it happens will help with a diagnosis.

If when coasting, the chain may be too long and bouncing off the selected sprocket.

If when back pedalling, (and using an external BB) you may have too many spacers on the wrong side of the bb, and pushing your big chain ring out too far, when you back pedal it will want to 'get in line' and shift down a gear.

If when load is applied it may be the shifter itself has a worn ratchet inside and is not holding the cable taught and shifting down.

All long shots.

 

[BM Epic]

Also if it is a dual suspension, is it shifting when hitting bumps or when load is applied to the suspension, it could be that when loaded your cable tightens and shifts, thus needing more cable where the suspension rocks, this is assuming that it is a duallie, this has happened to myself on a previous bike, took awhile to solve but it ended up being the cable that went under the bottom bracket, not enough of it, when it compressed it pulled at the cable, this is only a long shot, need to know more about the bike!