Another gear jumping question (sorry!)

telemark

Problem: Chain on road bike jumping to a different ring usually when putting only a little extra pressure on when climbing. This usually happens when using middle chain ring and cogs 5+6 at the back. Strangely it has changed both up and down by itself on different occasions, but more often changes to a higher gear (smaller cog). There's also been a reluctance for the mech to select the 5th cog in when changing down but trimming usually gets there. Otherwise changes are smooth and on request.

Gears: 105 triple chainset with new cassette, new cables and outers, new SRAM PC-1030 chain. The rear mech has about 5000 miles on it. The freehub has about 1000 miles on it.

What I've tried to fix it so far: Adjusted indexing till I'm cross eyed. Greased cable guides under bottom bracket. Examined rear mech by eye for alignment, damage, bends etc. Can't detect any adverse movement in either freehub or bottom bracket.

What next? Well, have mech checked by LBS? Replace mech? Change SRAM chain for Shimano or KMS chain? Possible the cable is too tight? How critical are the lengths of the cable outers - the 2 new outers are each about 2cm longer than the originals? Could the jumping be caused by a worn chain ring - not sure how but ...?

What am I missing here? Anyone got any hints?

nicklouse

sounds like a bit of extra friction in the outer.

un-clip the outers and lube them up with a light lube (with teflon etc).

CarlosDSanchez

I had the same problem with a sora mech, about 5000 miles on it also. Was fixed with new cables and outers + a device called a rollermajig (search chain reaction, they cost £5.99)

Now all shifting like new. You could also check the amount of play in the top pulley on the mech. There will be some side to side movement because shimano are designed that way, but if you can twist it from side to side or the teeth are very worn it will also make shifting harder.

telemark

Thanks for the replies folks. Have replaced cable and oiled the outers. Sadly no joy. Todays ride was punctuated on the hills by random gear shifting (up and down) especially when I using cogs in the middle of the cassette - not too much problem with the outer cogs.

I'm beginning to think the freehub is playing up - the wheel is not flexing or wobbling so the only place left where there's enough scope for flex sufficient to move the chain to a new cog has to be the freehub (unless the frame is about to give up the ghost which given the potholes round here wouldn't surprise me)

will3

Have you had a carefull look at the chain? I've had skippy chains which were caused by the chain starting to fail (ie a side plate had come off)

Also at 1000 miles I would think your jockey wheels will be a bit worn, especially if they've run dry.

telemark

Its a brand new chain - maybe 250 miles use. But I'll go and take a closer look. I couldn't see any stiff links when I looked earlier.

I wondered whether putting an SRAM chain (PC1030 10 speed) onto a Shimano 105 cassette would be ok. But I haven't found anyone (yet) who says it might be a problem. Easy enough to get hold of a KMC chain which I know does work just fine.

gbsahne001

will3 wrote:

Also at 1000 miles I would think your jockey wheels will be a bit worn, especially if they've run dry.

Can't see that, my bikes 13 years old and the bike has done over 10,000 miles; jockey wheels look fine

will3

gbsahne wrote:

will3 wrote:

Also at 1000 miles I would think your jockey wheels will be a bit worn, especially if they've run dry.

Can't see that, my bikes 13 years old and the bike has done over 10,000 miles; jockey wheels look fine

Sorry, obviously I meant at 5000 not 1000,

I guess it depends on how you look after it. Mine was knackered after 5000 miles, but then I was sloppy at oiling the jockey wheels and had been runnin fairly cross quite a bit.

telemark

Should have said I've already just replaced the jockey wheels so I think this time round maybe a red herring.

The (interim) culprit appears to be the freehub body which seems to have been reassembled (ie not by me!) without the right hand seal in place. I can only think the missing piece allowed just the tiniest movement of the hub, enough to throw the cogs all over the place and hence the jumping gears. It certainly let last night's hail storm into the hub ...

New freehub body on order (and will bring forward the purchase of a new set of wheels with those nice Hope bearings)

Thanks for the all the hints and tips

cyberknight

I have a similar problem with a sora 7 speed shifter, no matter how much i tweak the adjuster it does not down shift properly.I can get the upshift set so it is crisp but down shifting feels like i have to hold the lever in for a long time or shift it 2 times to get it to move,some times it jumps to far after that.

The rollermajig is discontinued at CRC i have found them on e bay from international sellers.

telemark

Does "down shift" mean for you:
a. moving to a larger cog, or
b. moving to a smaller cog?

If b then that sounds like a manky cable and/or outer and replacing both would probably sort it. Make sure there's no muck in the cable guide under the bottom bracket too - grease or oil there would be good.

If a then the cable is still possibly a touch too slack and turning the adjuster on the rear mech anti clockwise a little more would be where I would start.

I've found the instructions on the Parktools site are pretty good for adjusting derailleurs.

cyberknight

Yup tried all of the above and under workshop conditions i can get it to shift reasonably, as soon as i am on the road it is imprecise .

The shifter will click and some times nothing moves at all , then i reclick and it will jump further than it should .

telemark

OK so its load related and similar to my problem above. The next stop for me would be the hub although that would be coloured by experience of the Shimano freehub for my 105 setup.

What conditions are the bearings in? I've had uneven changes when the bearings needed attention after several extremely wet rides.

Is the freehub body firmly attached to the wheel? Again, somehow mine managed to come loose last year (probably something to do with a cracked ball bearing) and the changes were all over the place.

After that I'd look at the chain and the sprockets and the condition they're in. A worn chain gave me some fun until I thought to check it, and by that time the sprockets needed changing as well.

Bent chain ring? Rear wheel not seated straight in the frame?

One of things I've learnt over the last three years is the sheer quantity of different things that can affect smooth gear changes and when I think I've encountered them all something new crops up and surprises me.

Oh, and a last one - is the mech hanger straight and firm? I had a hanger fail slowly over a couple of days on another bike and the symptoms were similar to yours.

(Apologies if this is easy obvious stuff. If it doesn't get you any further forward hopefully someone will find it useful!)

cyberknight

re greased the bearings, new freewheel (its the old screw on style) , new chain ,all seated firmly .
Cables are the originals but i have run lube through the cable when detached to allow it to move into the outers.

I have been doing my own maintenance for close on 2 years as well so its only the really odd stuff that stumps me now, i am hoping the shifter is not on the way out, i see they still go for a wad of cash and if so i may as well flog the whole bike and stick to my mtb till i can afford a replacement .(bike was a 2nd hand purchase for £80 odd quid ).

Might take it down to the LBS over Easter as we have a week off if i cannot get it sorted.