Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

RD squeezing chain on biggest cog

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.

RD squeezing chain on biggest cog

Old 06-07-17, 08:17 AM
  #1  
mwib
Junior Member
Thread Starter
 
Join Date: Aug 2016
Posts: 18

Bikes: CAAD12

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
RD squeezing chain on biggest cog

After years of dreaming about it, I finally got a CAAD12 105 a couple of months ago. I've got about 1000 miles on it now. I've had it by the shop for a couple of quick tune-ups as the cables initially stretched and such, but would like to start doing these simple adjustments myself.

On my last ride, a couple evenings ago, I was unable to shift into into the biggest cog on the cassette. This morning, I got a chance to adjust the rear derailleur. It now shifts through all the gears -- but now the chain is squeezed between the jockey wheel and the cassette while in the largest cog. I adjusted the B-tension screw, but even with it screwed in all the way, there is rub. Anything other than all the way screwed in results in significant rub.

When I did the initial adjustment, I used only the barrel adjuster and some tweaks of the limit screws. I did not undo the cable from the anchor.

What's up here? Is this due to more cable stretch? Should I undo the anchor and pull the cable tight? Would doing this help pull the RD extended, away from the cassette? Am I completely off?
mwib is offline  
Old 06-07-17, 08:48 AM
  #2  
wphamilton
Senior Member
 
wphamilton's Avatar
 
Join Date: Apr 2011
Location: Alpharetta, GA
Posts: 14,536

Bikes: Nashbar Road

Mentioned: 65 Post(s)
Tagged: 0 Thread(s)
Quoted: 2507 Post(s)
Liked 55 Times in 33 Posts
I know it's unlikely at 1000 miles, but just in case if you've changed the chain length it might cause that. Also just to cover all the bases, you're not cross-chained while checking this, right? No bent hanger?

Otherwise, perhaps a longer b-tension screw, or I've heard of people screwing it in from the other direction to get more length out of it.
wphamilton is offline  
Old 06-07-17, 08:51 AM
  #3  
dsbrantjr
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Posts: 6,223

Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta

Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 654 Post(s)
Likes: 0
Liked 47 Times in 43 Posts
The cable tension (length, actually) adjustment is only to set the shift indexing, it will not have any effect on the rub you are experiencing.
The B-screw adjustment once set, should not need to be changed unless there is some material change in the drivetrain.
That, coupled with your sudden inability to shift to the largest cog, would suggest that something has happened to your drivetrain such as the derailleur getting bumped.
You should find out what has occurred before changing adjustments willy-nilly. Also, since you apparently have brifters you should check the shift wire inside of the brifter to ensure that it has not begun to fray. If it has begun to fray it should be replaced immediately; if the head breaks off inside the brifter you will play hell getting it out.
dsbrantjr is offline  
Old 06-07-17, 08:54 AM
  #4  
mwib
Junior Member
Thread Starter
 
Join Date: Aug 2016
Posts: 18

Bikes: CAAD12

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by wphamilton View Post
I know it's unlikely at 1000 miles, but just in case if you've changed the chain length it might cause that. Also just to cover all the bases, you're not cross-chained while checking this, right? No bent hanger?
No chain changes yet, and nope, no cross-chaining while adjusting / checking.

Otherwise, perhaps a longer b-tension screw, or I've heard of people screwing it in from the other direction to get more length out of it.
Hmm, interesting. Didn't think of that.
mwib is offline  
Old 06-07-17, 09:31 AM
  #5  
70sSanO
Senior Member
 
70sSanO's Avatar
 
Join Date: Feb 2015
Location: Mission Viejo
Posts: 1,321

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium DA, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 236 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
One thing you can do is slightly shorten the chain to see if it helps. Shift into the small chainring and large cog and pinch the chain to see if it pulls the derailleur forward enough and the jockey wheel away from the large cog. The chain may have always been a bit to long. I doubt if a tiny bit of chain stretch could trigger this, but who knows.

I just can't imagine a new stock drivetrain that would require a longer b screw if everything is setup properly. If no adjustment seems to work, I'd look into a longer hanger.

John
70sSanO is offline  
Old 06-07-17, 09:38 AM
  #6  
trailflow1
Senior Member
 
Join Date: Jan 2015
Posts: 377
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 100 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
What size cassette do you have and is the RD a short cage (ss) or long cage (gs) version ?

The B-screw may need to be reset if there was gap between the tabs when the RD was installed.

To reset it

Back the b-screw out all the way.
Loosen abit the RD bolt attached to the hanger
Push the b-screw tab up against the hanger tab and hold, and at the same time re-tighten the RD bolt.
Then re-adjust the b-screw for the 28t

Put the chain on the 11t cog while tightening the b-screw inwards (incrementally) then shift up to the biggest cog to check if it still rubs. You can spin the crank backwards and listen to how much noise the teeth are making. The keep doing the previous step,back and forth till the cog teeth/jockey wheel no longer make noise.

Last edited by trailflow1; 06-07-17 at 09:41 AM.
trailflow1 is offline  
Old 06-07-17, 09:38 AM
  #7  
JonathanGennick 
Senior Member
 
JonathanGennick's Avatar
 
Join Date: Apr 2007
Location: Munising, Michigan, USA
Posts: 4,009

Bikes: Priority 600, Priority Continuum, Devinci Dexter

Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 636 Post(s)
Likes: 0
Liked 4 Times in 3 Posts
Originally Posted by dsbrantjr View Post
That, coupled with your sudden inability to shift to the largest cog, would suggest that something has happened to your drivetrain such as the derailleur getting bumped.
I favor this explanation, and it seems worthwhile in this situation to rule out a bent hanger. Your shop will have an alignment tool, and it's a quick check to see whether the alignment is copacetic.
JonathanGennick is offline  
Old 06-07-17, 09:58 AM
  #8  
mwib
Junior Member
Thread Starter
 
Join Date: Aug 2016
Posts: 18

Bikes: CAAD12

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Thanks for all the replies. I'll be driving right by the shop this afternoon, so I'll bring the bike along and have them take a look at it.

I'll post an update about what exactly was going on.

Thanks again.
mwib is offline  
Old 06-07-17, 02:33 PM
  #9  
mwib
Junior Member
Thread Starter
 
Join Date: Aug 2016
Posts: 18

Bikes: CAAD12

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Update: The mechanic at the shop said he wasn't sure what the deal was. He said he'd seen this exact issue on a couple of their rental bikes last year with 105 RDs and admitted they "just put up with it" but acknowledged that wasn't an acceptable explanation for me. He told me he was going to get in touch with their Shimano rep. and told me to call back in a day or two to see what he was able to find out. It's almost as if the spring has sprung and isn't keeping the derailleur in the proper position.
mwib is offline  
Old 06-07-17, 03:34 PM
  #10  
70sSanO
Senior Member
 
70sSanO's Avatar
 
Join Date: Feb 2015
Location: Mission Viejo
Posts: 1,321

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium DA, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 236 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
IIRC... Old XTR 950 rear derailleurs had a weak b spring and would be challenged to run with a 32t after a while. I have not heard of a similar issue with 105's, but maybe the shop has experienced it.

John
70sSanO is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
CliffordK
Pacific Northwest
0
05-09-18 03:02 PM
bgblue1978
Classic and Vintage Bicycles: Whats it Worth? Appraisals.
3
03-04-14 10:41 PM
jkinvt
Introductions
4
02-02-13 08:52 PM
alcorso88
Road Cycling
13
10-16-09 09:54 AM

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


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.