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 09-28-11, 09:34 AM   #1
BikeManDan
Senior Member
Thread Starter
 
BikeManDan's Avatar
 
Join Date: Jul 2006
Location: Oakland, CA
Bikes:
Posts: 1,300
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Small ring sits too close to frame, FD can't shift into it

I'm a bit perplexed about this situation

Vuelta MTB triple with 110mm BB (as called for by the manufacturer)
The small ring apparently sits too close to the frame though because the front derailleur cannot shift into it; its at its travel limit (limit screw all the way out)

Longer BB?
BikeManDan is offline   Reply With Quote
Old 09-28-11, 09:36 AM   #2
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Bikes: Old Steelies I made, Old Cannondales
Posts: 19,854
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 189 Post(s)
Cable is not holding it back ?
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike
Homebrew01 is offline   Reply With Quote
Old 09-28-11, 09:45 AM   #3
kevin_stevens
Senior Member
 
Join Date: Jun 2011
Bikes:
Posts: 363
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
The BB/spindle length is to set the chainline front/rear so it clears the chainstay and lines up with the rear cassette/freewheel. If it's doing that, don't change it. The derailleur needs to fit that driveline, not the other way around. Take the cable off so you know the cage is under no tension, check for something jammed in the linkage, and see where it lies.

KeS
kevin_stevens is offline   Reply With Quote
Old 09-28-11, 10:35 AM   #4
rccardr 
aka: Dr. Cannondale
 
rccardr's Avatar
 
Join Date: Jul 2009
Bikes: I'd rather not count how many, thank you
Posts: 3,115
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 58 Post(s)
Had exactly this problem with my Dancelli road bike- FD couldn't get close enough to the seat tube to shift onto the small ring. This was caused by the seat tube being oval shaped and the FD being pushed farther out into the driveline than is otherwise typical. I tried changing the chainline but that was a disaster. What worked was experimenting with different FD's until I found one that had sufficient interios travel compared to the mounting point. For me, that was a Shimano 105 1055 series. Your results may vary.
__________________
Hard at work in the Secret Underground Laboratory...
rccardr is offline   Reply With Quote
Old 09-28-11, 10:40 AM   #5
dsbrantjr
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta
Posts: 4,653
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 89 Post(s)
BikeManDan: Are you certain you have loosened the correct limit screw? Detach the cable as suggested above and adjust the screw. You should be able to see the derailleur move as you do so. Also ensure that the derailleur cage is parallel to the chain rings.
dsbrantjr is offline   Reply With Quote
Old 09-28-11, 07:01 PM   #6
Camilo
Senior Member
 
Join Date: Apr 2007
Bikes:
Posts: 4,144
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 62 Post(s)
Assuming the limit screw and cable tension aren't the culprits, you might have to put some spacers on the drive side to push the whole crank that way. I had to do that with a frame once and it worked fine.
Camilo is offline   Reply With Quote
Old 09-29-11, 09:55 AM   #7
BikeManDan
Senior Member
Thread Starter
 
BikeManDan's Avatar
 
Join Date: Jul 2006
Location: Oakland, CA
Bikes:
Posts: 1,300
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
The proper limit screw is all the way out (not touching) and the cable is disconnected. The front derailleur is just not capable of reaching (Shimano XTR M950)

Adding spacers would be somewhat equivalent to installing a longer spindle BB, no? (say 113mm)
I have some 1mm spacers I could try. I haven't tried either of these because unfortunately the BB is seized into the frame (alu-steel).
BikeManDan is offline   Reply With Quote
Old 09-29-11, 10:35 AM   #8
rccardr 
aka: Dr. Cannondale
 
rccardr's Avatar
 
Join Date: Jul 2009
Bikes: I'd rather not count how many, thank you
Posts: 3,115
Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 58 Post(s)
If the chainline is correct (check Sheldon to be sure) than you need to change the orientation of the FD. Moving the chainline enough to enable the FD to shift to the inner ring will cause other problems unless you're talking about 1 or 2mm and even then you may run into trouble. Trust me on this- I've been to spacer/spindle land and it wasn't pleasant.

Are you using a triple FD?
__________________
Hard at work in the Secret Underground Laboratory...
rccardr is offline   Reply With Quote
Old 09-29-11, 01:16 PM   #9
Kimmo
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Bikes: copy/paste links: http://velospace.org/node/36949 http://velospace.org/node/47746 http://velospace.org/node/47747
Posts: 7,099
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Camilo View Post
Assuming the limit screw and cable tension aren't the culprits, you might have to put some spacers on the drive side to push the whole crank that way. I had to do that with a frame once and it worked fine.
I'd rather attack the FD with a dremel to get more travel out of it.
Kimmo is offline   Reply With Quote
Old 09-29-11, 01:30 PM   #10
BikeManDan
Senior Member
Thread Starter
 
BikeManDan's Avatar
 
Join Date: Jul 2006
Location: Oakland, CA
Bikes:
Posts: 1,300
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
I have the bike at a shop right now where they're taking out the seized BB (hopefully). I'll give a 113mm spindle a try

It's a triple FD. I said it was an XTR but I was thinking of something different, it's actually an STX.

Might be able to remove some material from the FD to increase travel, I'll check on that thanks
BikeManDan is offline   Reply With Quote
Old 10-04-11, 08:49 PM   #11
BikeManDan
Senior Member
Thread Starter
 
BikeManDan's Avatar
 
Join Date: Jul 2006
Location: Oakland, CA
Bikes:
Posts: 1,300
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Update (and conclusion)

Replaced the front derailleur with another 34.9mm. Still can't reach small ring with 110 BB. Installed 113mm BB, that did it. Very tricky but now working
BikeManDan is offline   Reply With Quote
Old 10-05-11, 03:09 PM   #12
mark03
Senior Member
 
Join Date: May 2011
Location: Seattle
Bikes:
Posts: 65
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I had the exact same issue with my '05 Sirrus Comp. I was changing the stock crank (compact double 50/34) to a 50/40/24 road triple. What I didn't realize, is that you are supposed to get a wider BB in this case, otherwise the middle ring will sit where the inner ring of the double used to be. Or something like that.

The thing is, I was perfectly happy with the chainline with the existing BB. Yes, it was displaced by 1/2 to 1 cog inward from the center of my 9-speed cassette, but I could argue that this was *better* for my gear usage, and at worst inconsequential. The problem was that stupid FD compounded by the fact that I needed a special one designed for flat-bar hybrids.

I ended up going the dremel route, but it was a lot more involved than just cutting away a bit here and there. I actually moved the two pivot points, and in the process used some JB weld, did some soldering, and learned to wind my own carbon-steel springs! The result is not pretty and may well fail after a season or two. When that happens I will probably have to do the "right" thing and change the BB. For the time being, it works great!

What is frustrating is that the Shimano FD designs are "lazy" in that they could easily provide more inward travel, but they don't. And because nobody specs this, without a box-full of FDs to try, it's nearly impossible to select one based on that criterion. All you will find from google or BF are answers to the effect of "well, duh, you need a different BB," but that really shouldn't be necessary.
mark03 is offline   Reply With Quote
Old 10-05-11, 03:29 PM   #13
MileHighMark
Old. Slow. Happy.
 
MileHighMark's Avatar
 
Join Date: Jan 2010
Location: Boulder County, CO
Bikes:
Posts: 1,798
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
What type of BB? Square taper? External? ISIS?

If it's a square taper or ISIS, you can add a spacer between the DS cup and BB shell.
MileHighMark 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 01:17 AM.