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rear derraillieur (sp?)

 
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slowpoke rodriguez




Joined: 11 Jun 2003
Posts: 1838
Location: Wales

PostPosted: Fri Nov 28, 2003 9:40 am    Post subject: rear derraillieur (sp?) Reply with quote

my rear derraillieur on my winter bike is not changing down quite enough ie when I'm on the biggest ring at the back (and middle on the front) it keeps trying to slip down to the next cog. Bearing in mind I'm usually only in this gear on a big hill this is the worst time for your gears to slip and is very annoying.

Can any of you bike techies tell me which knob I should tweak (oo-er missus) to fix it?
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ed_m




Joined: 15 May 2003
Posts: 8142
Location: coventry

PostPosted: Fri Nov 28, 2003 9:50 am    Post subject: Reply with quote

hi sp..

the mech is sprung toward the smaller cogs on the rear, so it is held in line as it moves to the larger ones by the cable tension.

if the cable stretches slightly it won't make it as far across as it used to making the chain try to slip off.... .. although if this is the cause it is likely to happen across the gear range getting worse as you go up.

first thing to try is to shorten the cable... not that you actually shorten the cable... rather lengthen the route it takes by unscrewing the barrel adjuster (usually on the shifter, sometimes somewhere on the cable run.. often also where the cable feeds onto the mech)...

if it only happens on the largest sprocket it may be that the cable tension is ok but the mech is being prevented from moving any further by the end stop.. these are adjusted using one of the two little screws on the mech (one for top end stop the other for bottom)... actually you can check for this case by putting the chain on the largest sprocket and seeing if you can push the mech any further toward the wheel.. if you can't then the cable is already pulling against the end stop and it may need adjusting..

hmmm ramble

in summary
1) put it on the large sprocket
2) push mech towards the wheel
3a) if you can move it, it's a slack cable... twiddle the barrel adjuster
3b) if you can't move it, it may be the endstop needs moving

ed
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Robert




Joined: 15 May 2003
Posts: 9238
Location: Back from outer space

PostPosted: Fri Nov 28, 2003 9:54 am    Post subject: Reply with quote

A-ha! Sounds like your rear derailleur's not aligned properly. Easy enough to do: change gear so that you're on the small chainring and large cog. Turn the pedals round - does the chain look like it's straining to stay on, i.e., not sitting on the sprocks properly? If not, adjust the screw on your derailleur until it seats correctly.

While you're at it, best do the opposite (large chain, small cog) and make sure that's not out of sync too.

BTW, I just remembered there are two screws on the read D. Without the bike in front of me, I can't remember which of them you need to adjust! Aaaargh Evil or Very Mad
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slowpoke rodriguez




Joined: 11 Jun 2003
Posts: 1838
Location: Wales

PostPosted: Fri Nov 28, 2003 10:03 am    Post subject: Reply with quote

cheers guys.
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slowpoke rodriguez




Joined: 11 Jun 2003
Posts: 1838
Location: Wales

PostPosted: Fri Nov 28, 2003 10:20 am    Post subject: Reply with quote

Ed, just checking the probably bleedin' obvious, but unscrewing the barrel adjuster presumably means turning it anti-clockwise? (The route of this daft question is two ruined spanners and a very stuck peddle when last trying to change peddles - I'm sure you know what I mean - ho hum, you live and learn Rolling Eyes )
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ed_m




Joined: 15 May 2003
Posts: 8142
Location: coventry

PostPosted: Fri Nov 28, 2003 10:26 am    Post subject: Reply with quote

well pedals have different handed threads on either side which would explain that one Very Happy

unscrew = anticlockwise.... on the shifter looking down the cable outer towards it... or on the mech looking down the cable outer toward the mech..... for ones elsewhere you're trying to make it l_o_n_g_e_r

Razz
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