Front changer trouble

[Dave W]

I have a tandem with a triple chainset on the front. changes fine on the stand but will not change down properly under load. Any tips? Does it help if the changer is angled?
It's doing my head in.

[meic]

Often in my case this was cured by fitting a new chain, after 2,000 miles they had too much sideways play and "snaked" around the dérailleur.

[Brucey]

what exact chain and chainrings are you using?

Is it just the big to middle, middle to small shift that are bad, or what?

cheers

[Dave W]

Lets have a look ..... it's got a shimano rear cassette nine speed looks like 105 and on the front it has a 105 changer with Alize 9/10 speed chain rings. The chain looks ok but I don't have a measuring tool. Previous owner reckoned it was new - it's a Tandem by the way. Chainging down I can get a complete neutral between the big ring and the middle where the chain simply won't mesh with the teeth. Sometimes the chain will throw off the inner into the frame but mostly I simply can't get onto the inner ring under load.

[reohn2]

Buy a N-gear Jumpstop:- http://www.billys.co.uk/english/group.php?prod=chng-js to stop it overthrowing the inner ring,when it happens on a tandem it can be serious.
What kind of shifters?
What type of front mech?
What size of chainrings?

The front mech cage should be in line with the chainrings( best way of doing it is to sight through with the mech in the middle ring position,from overhead the outer cageplate should be in line with the outer ring),and depending on chainring sizes 3 to 4mm clearance between c/ring teeth and mech cage.

[meic]

It is possible that you do not have it set up correctly.

I had a lot of brain ache setting up a Dura-Ace front STI controlled dérailleur as there were so many different possible trim settings and you could get fooled into mistaking (for example) middle ring on outer feathering for outer ring on inner feathering, especially as they dont seem to be in the same place going up the gears as going down.

I dont know if 105 are equally complex?

[Dave W]

105 shifters. I have a chain catcher to stop it smashing into the frame. Could be the sideways play in the chain I suppose, everything else looks ok including the gap to the teeth. The cogs look like new, it all looks fine to the eye.

[reohn2]

105 road STI's(?) have four clicks for three rings one is a trimming click.
Release the four clicks so there is no more and the chain is on the granny ring.
release the cable from the front mech.
put the rear mech in bottom(biggest cog),the chain should now be jjuusstt clearing the inside of the inner cageplate,If not adjust it so it is,with the limitscrew on the mech.
Pull the slack out of the cable and reconnect to the mech,ensuring its on the correct side of the pinch bolt,(if it isn't it won't change correctly).
Now try it,through to the big ring.
It should be OK.

[Brucey]

if the TA rings are fitted to an older spider there is a small chance that this may leave them slightly further apart than they should be which might explain the 'neutral'/riding problem. Likewise if one of the chainrings is fitted the wrong way round or damaged or something.

I'd suggest measuring the chain width with some verniers to check that it is the correct one, too.

The failure to derail from the middle to the small chainring could be an issue with the fit of the chain onto the middle chainring. If the chain is too snug on the chainring (i.e. less than ~0.2mm width clearance) then it won't necessarily derail easily. A reduced clearance could be from a mismatch between the chain and chainring, or damage (e.g. burrs) on the chainring teeth.

The other thing that might do it is if there is too much friction in the cable; the front mech may not move with sufficient enthusiasm, so the shift works under benign conditions but not when you need it to. Campagnolo have a specification for the cable force at the shifter end arising from the mech return spring but I'm not sure Shimano have a similar spec.

hth
cheers

[Dave W]

It's one of the problems buying second hand I don't know exactly what's been fiddled with. The bike although looking near immaculate is a pig at the moment. The rear cassette was changed from the original to give a better range, the rear mech was changed from 105 to XT I'll try and find what the chain is, could be it's a ten speed instead of a nine or something daft. I've never had a complete nuetral before where the chain will not mesh with the teeth on any other bike.
Thanks for your help so far

[Dave W]

Well started to reset the changer then realised it was dropping every time I shifted - turns out the thread is knackered where it bolts on to the braze on type clamp. New one on order

[meic]

You may wish to kill me, or be grateful for this.

http://www.chainreactioncycles.com/Mode ... elID=13623

http://www.chainreactioncycles.com/Mode ... elID=13626

[Dave W]

Bottom one was ordered (braze on).
Just paid £35 for a ten speed on my Roubaix too.

[Dave W]

Bendy or normal?



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[PT1029]

From the photo, front mech as viewed from above looks good (not rotated round on seat tube).
3 things to check
1. The mech is at the correct height (1-3mm gap between top of outer ring teeth and underside of outer edge of front gear cage when outer edge is just above the outer ring teeth).
2. Has the front ratios been made wider than standard? Photo suggests they look fairly normal, but making them wider (bigger outer ring/smaller inner ring) can make changing less precise - especially re mid/small ring, as the chain is pushed by the gear cage further away from the chain ring.
3. Thinking of a member in our local CTC group, check the chain rings are on the right way round!!

Also, the elephant in the room which no one has mentioned, you say it won't change under load , well, however you set it up, how ever expensive it is, it won't want to change under pressure! Plan ahead and change early (before it gets steep), or give 2 or 3 hard pushes on the pedals to give you enough momentum so you can then ease of momentarily while you - with exact timing - change down.