What does it mean if... (chain jumping between gears)...

[Manc33]

On a new cassette (old one shifted gears well and the chain has done under 100 miles) its jumping between gears sometimes depending on how the cable tension is adjusted.

It can be on the outer chainring (of a triple) and the highest gears on the cassette and jump, so I wind out the barrel adjuster and it fixes it. Then I go to the middle chainring and 2nd lowest sprocket and there's a tinkling noise because the cable is slightly too tight, I loosen it slightly and it again causes it to skip (and not have enough tension) on the outer and high gears. It seems the only working option is to have it tinkling, but it is almost changing onto the lowest sprocket.

Its like the cable isn't being released properly from the biggest sprocket to the next one down. Whats annoying is I didn't touch the mech or shifter, or cable and the cassette I took off shifted well. I think its hit and miss with the machining on these cheaper cassettes (although the cheap cassette I took off, is a groupset below the new cheap one I put on).

Maybe the old mech just isn't as springy these days and isn't releasing the cable with enough force but its an old grey XTR mech, do they ever do that? A new spring in the parallelogram shouldn't cost much and I think I might be able to replace that myself.

The mech being a bit sloppy seems to explain the symptoms, apart from that I have only swapped the cassette and yes it was put on gorilla tight lol. I think a newer mech might be a better bet. Its always seemed to need to have a tight cable tension on the rear derailleur and that would suggest the cable isn't being released with enough force by the derailleur, hence needing the cable slightly too tight. Normally its a case of just putting a new cable in - but the cable is relatively new and wasn't touched, apart from the slight cable adjust at the barrel adjuster, for the new cassette.

[Chris Jeggo]

This sounds exactly like a problem I had recently. I replaced a 9-speed (chain and) cassette (all working OK but worn) with a Shimano Alivio HG400 12-36t 9-speed cassette. Investigation revealed that the sprocket pitch and cassette width were less than quoted by Sheldon Brown https://www.sheldonbrown.com/cribsheet-spacing.html. I just needed to get it working so I dismantled the cassette, made some shims (0.1mm thick) from an aluminium beer can, respaced it and re-assembled. It worked so I did not investigate further.

[Brucey]

the other thing that will cause such symptoms is if the rear mech isn't quite aligned properly (eg at the hanger or if the mech is slightly bent); in combination with a larger interval between sprockets this can cause the issues described.

It is also possible (through wear or damage) for the upper pivot in a rear mech not to be aligned with the lower pivot in the mech. The result of this is usually that the pulleys are only perfectly aligned with the sprockets in one gear per chainring (and never the same one).

Finally it is as well to note that chains can vary in width very slightly (as well as enthusiasm to shift) and this affects the tolerance on everything else.

cheers

[esuhl]

Could it be that the "B screw" needs tightening to take up the slack on the smaller gears?

https://www.youtube.com/watch?v=QRhKaZd6GWQ

[Manc33]

Its a 11-34t and it seems to be something to do with pushing the b-tension perhaps, but I already have a reversed allen head bolt in the b-tension, nearly on its limit against the hanger. All I can do is try to get that screwed out even more (where screwing that out means in because its reversed lol). I found those allen bolt head the best for getting a bit more b-tension. http://i.imgur.com/zbfT3nY.jpg (can't remember the size). I was thinking perhaps the M772 might be a better bet than the M952 but I detest taking XTR off my bike lol.

The M772 is perhaps a faster shifting mech than a M952 I don't know, but its b-tension can be locked in place, to perfection, along with all the other stuff its good for, but I always think the old grey XTR stuff will last longer. Its shifted like a dream on my 11-32t cassette but I put a 11-34t on and, the first post.

It might even be a kink in the cable is affecting something that wasn't, but the tension hardly needed to change from old cassette > new.

If I put it on the smallest sprocket and move the shifter slightly (without fully shifting to the next sprocket) the rear mech should return back to where it was, but doesn't, I think my housing is too short possibly. Putting a new cable in with longer housing is one thing but I hope its not the main mech spring thats weak.

[Annoying Twit]

This sounds exactly like a problem I had recently. I replaced a 9-speed (chain and) cassette (all working OK but worn) with a Shimano Alivio HG400 12-36t 9-speed cassette. Investigation revealed that the sprocket pitch and cassette width were less than quoted by Sheldon Brown https://www.sheldonbrown.com/cribsheet-spacing.html. I just needed to get it working so I dismantled the cassette, made some shims (0.1mm thick) from an aluminium beer can, respaced it and re-assembled. It worked so I did not investigate further.

I can't contribute sensibly to this thread, but I really wanted to give you some positive feedback fro making shims from an aluminium beer can. I salute your engineering spirit.

[Manc33]

There's nowhere to shim in my case. I'm not putting shims between sprockets and starting all that when the last cassette worked perfectly.

If it were to have a shim, it would be between the 2 largest sprockets, because thats where its trying to shift up (the tinkling noise) when it shouldn't be.

It is making that tinkling noise on the 2nd lowest sprocket because the cable has to be that tight for it to shift properly between the 2 highest gears on the outer chainring.

After looking at it more, the rear mech can be pulled slightly and its stays in that position. Thats not good, its either a kink in the cable or my rear mech just can't cope with a 34t (although its the M952 thats meant for a 32t-34t low).

I am sure a lot of these shifting issues come from having the cable touching something along its entire length. "But my bike looks nice and neat" yup. I'd rather have it working properly though, looks come second for me.

All I can say is what everyone says, check the cable housing isn't too short first of all, then put a new cable in after making sure the housing is long enough. Its the all time argument lol, a long loop of housing or a short one. Its mind boggling lol.

[Manc33]

After cleaning out the internal cable routing to the rear mech (by dripping oil down it and pulling a deliberately frayed cable through many times, until the oil was only about 10% as dirty) and lengthening the cable housing to the rear mech and taking the bike computer wire away from being wrapped around the rear shifter housing and putting in a new cable - it is still exhibiting the symptoms it was before, but it is not as bad as it was.

There's too much friction on the internal cable guide.

When it was housing > nothing > housing this never happened (like on every old road bike ever) but with it internal its a pain for rear shifting! Its as if it needs filling (injecting) with a thick grease. Where's the cake icing nozzles. Pipe some of that blue Park Tool grease down it. The oil I did use was Tri-Flow since its got that Teflon stuff in or whatever it is, PTFE.

It is now running through the gears successfully - but its balanced on a tightrope regarding the barrel adjustment.

- Two 1/8th turns out of the barrel adjuster has the chain tinkling against the low sprocket and wanting to shift to it when on the 2nd lowest sprocket.

- Two 1/8th turns in of the barrel adjuster has the chain swapping on and off the 11t and 13t cog at the other end while on the outer chainring after clicking once to shift to the 13t from the 11t.

Its swapping on and off those sprockets because the other end was adjusted (cable loosened off) to stop the tinkling noise against the lowest sprocket.

It is all caused by the friction of the internal cable routing and the mech not being able to return back due to the friction on the cable. Maybe a Teflon cable might fix it. The irony since internal routing is meant to stop dirt getting in, a cause of friction!

Still can't setup the b-tension (probably my derailleur hangars fault) even with a reversed allen head bolt being used on the b-tension. I have a suspicion the RD-M772 will solve that, but I see it as a downgrade from the M952.

If the rear mech isn't strong enough to return itself back from the cable friction... it will surely slowly go back as I ride along in that gear?

[Samuel D]

Lengthening the rear loop of housing will not reduce friction and may increase it (if the cable is turned through a greater total angle by bulging out farther than needed and then coming back on itself). At least for new cables; cables with tighter curves may wear more quickly and suffer a greater increase in friction as they age, for all I know.

Read this fascinating blog post for more.

Because the total change of direction is the important thing, the rear loop of housing just before the derailleur often causes more friction than the rest of the cable combined. It is worth making sure the cable moves very freely in that foot of housing.

Reohn2 of this forum recently mentioned a technique for cleaning and lubricating the cable in this rear loop. Engage first gear, then move the rear shifter to top gear without turning the pedals, to generate lots of slack in the cable. Then unhook the housing from the chainstay stop and slide it up the cable, toward the bottom bracket. This exposes the cable for greasing. I use Shimano Cable Grease, designed for the purpose and highly effective. I’m cautious about using any old lubricant, since many of them gum up when mucky water gets in.

[Manc33]

Cheers, I never stop learning.

One thing I might do (because I can't see why this won't work) is just cable tie an entire length of housing onto the frame, along where it goes internally.

If it is kept straight and tight with enough cable ties like every 6" I can't see why this won't work.

It doesn't need to look neat and it wouldn't. I can't run the housing through the frame without drilling the cable guides out and I'm not doing that. Running housing through the frame will possibly cause that internal cable routing rattling we all love so much, whereas simply cable tying the housing to the frame will fix that, its firmly attached to the frame.

Also because its cable tied and isn't running through loose, it won't be changing gear on me because I am steering, which was another problem I read some had when going to full housing @ the rear mech.

People spend ages working out how to get around the friction problems to the rear derailleur on internal cable routed frames, then how to stop the housing sliding through while riding and turning the handlebars. My frame is carbon and I am running the bare cable through the frame at the moment, its got too much friction for the rear mech to properly collapse back to position, I am sure its cable-against-carbon, the friction is just too much.

The same could be done with the front derailleur and maybe even the rear brake but thats overkill. Then you have holes in the frame where the cable housing should go - but that can be plugged with something to stop the elements getting in the frame's "mini-tubes" (?) for the internal gear cable.

I have seen a cutaway cross section of a frame with internal routing and if the cable is shifting against carbon, can't have that. The inside of cable housing is I am sure going to be more slippery. The cable, shifter and rear mech doesn't care that the housing is strapped with cable ties to the outside of the frame. I don't care if it looks awful, I am sick of this stiff shifting.

At some point I will get 2M of SP41 housing along with a Teflon XTR cable, since people seem to say there isn't much better.

[Manc33]

I reckon cable tying gear housing to the frame for the rear derailleur won't work, the outside of the housing is hard plastic and I can't see how it could be stopped from slipping.

I test rode it the other night and it ran perfectly so I might leave it but I definitely have too much friction on my cable. One fix might be the M810 derailleur since its advertised as having a 10% stronger main return spring compared to XT/XTR. Its also handy because its adaptable to suit a 11-23t or 11-34t. Its also got that locked b-tension (the p-tension is the b-tension it seems). The only downside to it is you can only get that in a GS and I have a 45t capacity, thus the M772 (or M972) are better options, but I see the XTR as a waste of time/money, it feels fragile in use leaving only really the M772 as the best option.

The thing is a little bracket attaches to the frame then the mech is attached to that bracket on those newer shadow mechs. On older mechs like the 8-speed LX/XT/XTR the actual metal body of the mech itself clamps directly to the frame, making it solid. Its got less play than the newer ones, because it just has to have, there's no added bracket on the older mechs.

I alleviated probably 30% of the friction (by lengthening the rear loop that was admittedly a bit straight going into the mech) but I know its still not fully there yet. The old M952 has a screw on it you can adjust the main spring tension but thats adjusted to the most strength already.

[Ash28]

I had a similar problem i.e chain randomly jumping around the middle of the cassette,usually when going uphill . I did two things, one or both of them cured it. I changed the rear mech and I cleaned and lubricated the plastic cable guide under the bottom bracket.

[Brucey]

Lengthening the rear loop of housing will not reduce friction and may increase it (if the cable is turned through a greater total angle by bulging out farther than needed and then coming back on itself).....

Read this fascinating blog post for more......

I think he is very quick to conclude that this is correct. However the data is plotted a bit weirdly, it has no error bars, there is scatter (which at 270 degrees suggests it is significant), and if you look at the data point for 210 degrees, (taken with a baggy loop) it looks as if it might fit a different distribution vs the data point for 180degrees.

The thing that cannot be allowed for very easily in such tests is the fact that with a long baggy loop, the cable housing is far less likely to develop a kink at either end. Kinks are incredibly good at generating friction. Also there is no such thing as a perfectly straight run with no friction; the inner will always be touching the sides of the housing on the way through.

BTW the coefficient of friction is not linear with load or speed, and everything changes when you use a different lube. I believe the housing he was using should have had grease in it; using a random oil instead could have done a number of things including soften the liner.

BTW the capstan equation strictly applies to static friction rather than dynamic friction. I'm not saying that static friction isn't relevant to gear cables, but it isn't what was measured by the blogger.

cheers

[Manc33]

I worked out the reason it was happening, the cable had just not settled down properly. Once it got settled it all went away, although its only just running properly.

If I turn in the barrel adjuster 3 notches I will have it jumping around on the 11-13-15t cogs when on the outer and if I undo the barrel adjuster 1 or 2 notches I will get the chain making a really light tinkling wanting to change from the 30-34t.

I figured if I can wheel it backwards on the 30t without the chain doing anything it shouldn't (while it is also OK forwards), then its settled and it seemed OK but, I know its running on a tightrope!

When my housing gets a bit of friction in it from use I will soon find out. It could be because they are XTR shifters and have hardly any margin for error, but no because this only happened when I swapped from a 11-32t cassette to a 11-34t.