tweaking MIDDLE chainring indexing

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tweaking MIDDLE chainring indexing

Postby didds » 09 Jan 2010 15:55

OK - I understand about low derailleur adjustment screws looking after the inwards shift on the small chainring, and the H screw looking after the outward shift on the large chainring.

but the web goes strangely quiet when it comes down to moving from small to middle and middle to large.

(FTR My MTB (Decathlon 5.3) drivetrain is Suntour XCM 302 aluminium 22x32x42 chainset. SRAM X-5 9 speed shifters. Shimano C050 front derailleur. SRAM X-5 rear derailleur. SRAM PC951 chain. SRAM cassette. )

what do I need to do to get smooth transition from small to middle and middle to large - at the moment I can just get small to middle if I move the indexing from 1 (small ring) right through to 3 (big ring) but then i can;t get it from middle to big. This has only just started, but in effect the bike is still pretty new and I suspect this is just down to cable stretch.

cheers

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Re: tweaking MIDDLE chainring indexing

Postby simondo3333 » 12 Jan 2010 09:38

Have you tried adjusting the cable tension at the shifter?

There should be a threaded barrell where the cable runs into the shifter housing. Just a half or single turn should help sort it. Also if you can't shift to the big ring from the middle then a slight turn of the upper limiter screw should help without the chain flying over the ring if you shifted straight from the small ring, its likely to be the momentum of the chain thats allowing it onto the big ring at the moment so only needs a very slight adjustment by the sounds of it.

Its usually trial and error with indexing, slight adjustment, test, slight adjustment, test, and so on. Easy if you have a bike workstand but a bit more difficult if not.

If the bike is still relatively new then cables shouldn't need lubing I wouldn't have thought, but worth checking if the above doesn't help.
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Re: tweaking MIDDLE chainring indexing

Postby didds » 12 Jan 2010 13:10

simondo3333 wrote:Have you tried adjusting the cable tension at the shifter?

There should be a threaded barrel where the cable runs into the shifter housing. Just a half or single turn should help sort it.


this IS the sort of advice I need ... I KNOW there are barrel adjusters but having in 2008 !tweaked" my indexing on my 1st road bike to them spend the next 9 months never getting them working properly I am really really loath to touch the stuff. I've watched you tuve videos, I've read "Zin and the art...", I've perused Sheldon Brown... and while they all just go quarter of a turn here and half a turn there and everything just works my experience is that I am crap! I'd do the bike maintenance day but I am already booked that weekend elsewhere - so all advice is great!

Q: which direction twistiug the barrel adjusters does what to the chain?

cheers

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Re: tweaking MIDDLE chainring indexing

Postby Bopomofo » 12 Jan 2010 15:44

Didds... check on YouTube for the video of the man in slacks showing how to adjust a rear. Same principles apply to the front...

1. Release everything, including cable grip. Screw the barrell adjusters right in.
2. Grab the ARM and shove it against the end stops in each direction and adjust the screws until perfect.
3. Take up the cable slack, tighten the grip. Adjust the barrel thing until it starts jumping then back off until perfect.

By the magic of indexing your middle cog is now spot on.
I had fun once. It was awful.
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Re: tweaking MIDDLE chainring indexing

Postby simondo3333 » 14 Jan 2010 14:45

didds wrote:
Q: which direction twistiug the barrel adjusters does what to the chain?

cheers

didds



I think turning it clockwise as you look in the direction of the cable entering the shifter takes up the slack in the cable. You should be able to tell from direction of the thread on closer inspection. Bopomofo's advice is sound but if it is a slight stretch in the cable then the barrell adjuster should be your first check as you could end up doing more work than you really need to and potentially spending the next 9 months using only 5 gears or someting that work properly ;)

The barrell adjuster just adjusts the cable tension, nothing else. Although the effect of a slack cable means it won't index shift properly as the slack is taken up in the shifter and the derailleur isn't allowed to do its job fully without the cable being relatively tight. The limiter screws on the derailleur body just stop the chain flying over the top ring or over the lower ring depending which rings you are shifting from/to - if this was fine previously then they shouldn't need messing with.

If in doubt take it to a LBS and ask to watch them do it from scratch, its probably the most difficult thing in bike maintenenace after servicing suspension and bleeding hydraulics (RE MTBs), so once you nail it a few times it is gratifying to be able to do it yourself.

Good luck.
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Re: tweaking MIDDLE chainring indexing

Postby didds » 14 Jan 2010 16:14

simondo3333 wrote: The limiter screws on the derailleur body just stop the chain flying over the top ring or over the lower ring depending which rings you are shifting from/to - if this was fine previously then they shouldn't need messing with.


that was my understanding entirely and the chain doesn;t drop past the small/large chainring (well it doesn;t on the small band it DIDN'T on the large ... given I can;t get it up into the large ring now :-). Which is rather why I asked as I didn;t want to break something that isn't broken really... its this middle ruing mularkey that was confusing me and was proving so difficult to find any info on.

Cheers all!

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Re: tweaking MIDDLE chainring indexing

Postby simondo3333 » 14 Jan 2010 17:07

I'm sure the BCTTT maintenance day will be best bang for buck but this is also worth a punt if you are in need of maintenance training

http://www.bikeradar.com/mtb/news/article/win-a-home-mechanic-course-worth-250-24610

Also some pictures and further advice to compliment what Bopomofo and I have said so far.

http://www.bikeradar.com/gear/article/workshop-how-to-set-up-the-gears-on-your-bike-23582
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Re: tweaking MIDDLE chainring indexing

Postby didds » 14 Jan 2010 22:30

ta muchly all round... did the barrel adjustment jobby and its done the trick luvley :-)

can't make the bike maintenance day as i away that weekend...
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