Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 04-16-12, 06:14 PM   #1
eliott
Junior Member
Thread Starter
 
Join Date: Feb 2012
Location: Toronto, Canada
Bikes: Department store Schwinn turned frankenbike, 1986 Bianchi Strada, fixed gear with 1980 Canadian custom road frame
Posts: 15
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Rear derailleur cable tension - from too lax to too tight in a couple of shifts

Hello all. I'm hoping someone might be able to suggest where the problem with my rear shifting system lies. I've tinkered with the whole system for hours, followed setup advice in books (limit screws, indexing, B screw, etc.) and taken the bike to a mechanic, only to have the shifting fall apart a few blocks afterward.

I've replaced the following parts with brand new items:

1. Rear derailleur itself (Altus for Deore)
2. Derailleur hanger
3. Housing
4. Cable
5. Chain (length was determined using a few online calculators)

Whether it's the old Altus or the new Deore; the new or old chain, the problem is this: the cable has to be set so loose at the smallest rear cog that it almost strikes the chain in order for me to be able to shift upwards at all. By the time I'm close to the larger rear cogs it is almost impossible to push the shifting lever (and I wouldn't try). The cable by this time has become way too tight.

If I try to readjust and loosen the cable a tiny bit, then shifting around the smaller cogs is completely useless - the rear derailleur doesn't move at all because the cable is so loose.
eliott is offline   Reply With Quote
Old 04-16-12, 06:29 PM   #2
CACycling
Senior Member
 
CACycling's Avatar
 
Join Date: Feb 2008
Location: Oxnard, CA
Bikes: '08 Fuji Roubaix RC; '07 Schwinn Le Tour GS; '92 Diamond Back Ascent EX
Posts: 4,565
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Take it back to the mechanic. Or at least post a picture of the RD/cog area of the bike so we have some idea what you are dealing with.
CACycling is offline   Reply With Quote
Old 04-16-12, 06:30 PM   #3
jim hughes
Senior Member
 
Join Date: May 2010
Bikes:
Posts: 461
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
At first hearing, this sounds like a compatiblity problem. Is the shifter also Shimano? Does the number of cogs (6/7/8) match the shifter?
jim hughes is offline   Reply With Quote
Old 04-16-12, 06:37 PM   #4
IthaDan 
Senior Member
 
IthaDan's Avatar
 
Join Date: Jan 2012
Location: Ithaca, NY
Bikes: Click on the #YOLO
Posts: 4,871
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Sounds like your low limit screw is too tight.
IthaDan is offline   Reply With Quote
Old 04-16-12, 06:48 PM   #5
onespeedbiker
Retro Grouch
 
onespeedbiker's Avatar
 
Join Date: Oct 2007
Location: Santa Cruz
Bikes: Yes
Posts: 2,210
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I'm thinking you did not upshift the shifter to the last gear before you anchored the cable to the derailleur. If you have any doubts, unscrew the anchor nut for the rear derailleur cable and press down the rear shifting lever repeatedly until you know it can upshift no further than re-attach the cable and see if it works better..
onespeedbiker is offline   Reply With Quote
Old 04-16-12, 06:57 PM   #6
eliott
Junior Member
Thread Starter
 
Join Date: Feb 2012
Location: Toronto, Canada
Bikes: Department store Schwinn turned frankenbike, 1986 Bianchi Strada, fixed gear with 1980 Canadian custom road frame
Posts: 15
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thank you. The shifters match the 8 cogs in the back - both parts came with the original bike and they're Shimano too (the old cassette *was replaced at the lbs with the exact same one about five months ago due to wear). I'll try loosening my low limit screw now and see if that helps.
eliott is offline   Reply With Quote
Old 04-16-12, 06:59 PM   #7
eliott
Junior Member
Thread Starter
 
Join Date: Feb 2012
Location: Toronto, Canada
Bikes: Department store Schwinn turned frankenbike, 1986 Bianchi Strada, fixed gear with 1980 Canadian custom road frame
Posts: 15
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Onespeedbiker...sorry, I missed that reply. I'll try this as well.
eliott is offline   Reply With Quote
Old 04-16-12, 07:26 PM   #8
jim hughes
Senior Member
 
Join Date: May 2010
Bikes:
Posts: 461
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Find the adjustment procedure on the Park Tool web site and follow it exactly. Can't fail.

In that procedure, you set the limit screws first, without using the shifter, independent of indexing.
jim hughes is offline   Reply With Quote
Old 04-16-12, 08:17 PM   #9
dsbrantjr
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta
Posts: 4,583
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 59 Post(s)
Quote:
Originally Posted by jim hughes View Post
Find the adjustment procedure on the Park Tool web site and follow it exactly. Can't fail.

In that procedure, you set the limit screws first, without using the shifter, independent of indexing.
Start at the beginning as if it is a new installation. DO NOT skip any steps. Adjust screws and barrel adjusters in 1/4 turn increments maximum, 1/8 turn preferred so you don't overshoot.
dsbrantjr is offline   Reply With Quote
Old 04-17-12, 09:37 AM   #10
Retro Grouch 
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Bikes: Rans Rockst (Retro rocket) Rans Enduro Sport (Retro racket) Catrike 559, Merin Bear Valley (beater bike).
Posts: 26,614
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 88 Post(s)
A couple of things you have said make me wonder about the chain length. I'm a proponent of the big/big, bypass the derailleur, figure the shortest place you could rejoin the chain, and add 1 inch of chain to that.
Retro Grouch is offline   Reply With Quote
Old 04-17-12, 10:08 AM   #11
KevinF
Keep on climbing
 
Join Date: Apr 2004
Location: Marlborough, Massachusetts
Bikes: 2004 Calfee Tetra Pro
Posts: 2,136
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I've also seen some very strange things occur if the shifting cable isn't attached to the rear derailleur at the right place. They seem to be pretty finicky about exactly where the cable is attached.
KevinF is offline   Reply With Quote
Old 04-17-12, 11:48 PM   #12
Jeff Wills
Insane Bicycle Mechanic
 
Jeff Wills's Avatar
 
Join Date: Mar 2008
Location: other Vancouver
Bikes:
Posts: 7,944
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 16 Post(s)
The cable should not be loose with the chain on the smallest cog. There should be some preload on the cable.

Try this: shift the chain to the second-to-smallest cog. Stop the wheel, then click the shifter into high gear. The cable will go slack. Loosen the hold-down bolt, remove the cable slack (don't pull hard), and tighten the bolt. Now turn the cranks- the chain should shift into the smallest cog.

This will give you a baseline adjustment. Now fiddle with the barrel adjuster so the derailleur pulleys align with the cog. (It should be close.) Keep checking to see that one click of the shifter moves the chain from the smallest to the second-smallest cog and back again. Once that's done, check the rest of the cassette. It should engage/disengage all of the cogs equally.
__________________
Jeff Wills

Comcast nuked my web page. It will return soon..
Jeff Wills is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 02:28 PM.