Rear derailleur rubs, shorten chain??????

Discussion in 'Mountain Biking' started by PellConq1, Jul 29, 2010.

  1. PellConq1

    PellConq1 Member

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    Mt. Fury Roadmaster - a set on Flickr

    My pictures show a perfectly good Mt. Fury Roadmaster except for one thing. When the front sprocket is on the smaller two of the three front sprockets (and even some when it's on the other, just less), the derailleur rubs as shown in the picture (in other words, it's pinched up). So could the first step to solving the problem simply be:
    1) Take some links out of the chain (this is something I'm good at doing, I've done it on several bikes now).

    Or is there some simpler way to fix the problem?
    Just curious.
    Enjoy.
    Pell http://www.twospoke.com/forum/images/smilies/smile.gif
     
  2. Industry_Hack

    Industry_Hack Total noob (& forum admin) Admin Staff Tavern Member

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    I'm not following you. Are you cross-gearing? When on the inner chainrings, you should be on the largers cogs. When you are on the outer chainring, you should be on the smaller cogs. If you try to use a small chainring with a small cog, you will run into clearance issues.
     

  3. PellConq1

    PellConq1 Member

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    Derailleur pinched up reply

    I haven't messed with anything yet on the Mt. Fury - at all. I was just commenting something like, "What would you do FIRST if you came across a Mt. Fury Roadmaster in a junkyard and it had the problem shown in the picture - ie. a rear derailleur with pulleys too close for comfort."

    Anyway, I just read up on terminology on Wiki. So to rephrase the problem:
    On the rear derailleur, the tension pulley (the lower one) is too close to the guide pulley (the upper one).

    So here goes for my dumbest attempt to fix:
    1) Cables too stretched, simply readjust the pinches of the cable (or more drastically, replace the cable or cut it shorter, just kidding, I wouldn't do that)?
    2) Chain too stretched (I don't mind taking links out of a chain provided I
    don't lose too many gears).

    I just wanted someone to give me their opinion on the matter since I didn't feel redoing the chain yet, but frankly, many bike problems go away when we shorten those old, overstretched chains.

    By the way, I'm not worried about this, I'll tinker with it and fix it somehow. Something will start working eventually, it's just no fun riding a bike when only certain gears ride smoothly and others rub.

    Thanks for your kind response. I'll look into this after I change some tires on another bike.
    Cheers!
     
  4. PellConq1

    PellConq1 Member

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    Yes, yes, you're right - small/small is when the problem happens, you have it right! Sorry, I forgot to comment on what you said. Thank you.
     
  5. Industry_Hack

    Industry_Hack Total noob (& forum admin) Admin Staff Tavern Member

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    Shortening a stretched chain doesn't fix anything. But as you've pointed out, it is merely an issue of cross-gearing.

    You to bike doctor: "It rubs when I do this"

    Bike doctor: "Don't do this"

    ;)
     
  6. PellConq1

    PellConq1 Member

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    But do this is what I want to do - ?????

    When you speak of cross-gearing, you make it sound like it's something we shouldn't do. Isn't a 15-speed mountain bike supposed to work in any combination of front/rear sprockets so that there are 3 x 5 = 15 gears in all? Are you suggesting avoiding certain front/back combinations? Something is wrong with the bike and I want to fix it so I don't have to avoid. You said "Don't do this" - what did you mean? I'm confused. What do you mean by cross-gearing and isn't cross-gearing ok?
     
  7. Industry_Hack

    Industry_Hack Total noob (& forum admin) Admin Staff Tavern Member

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    Small chainrings are to be used with large to middle cogs. Large chainrings are to be used with small to middle cogs. Cross gearing places the chain at an extreme angle, causing accelerated chain/chainring/cog wear.
     
  8. PellConq1

    PellConq1 Member

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    TwoSpoke update - fun with gear ratios and SRAM MRX shifters

    Well, I got the message that I haven't been Two-Spoking so here's an update in my bicycling:

    I haven't had to look at this issue in many years but one thing I've never done relative to your cross-gearing comments is: exactly what are the 15, 18, or 21 gear ratios on a typical mountain bike or Mt. Fury Roadmaster for example? I had never even thought about this - I just ride the bikes and fix them when they break but I never really thought about what gear combos are the best.

    In the meantime, I just ordered some Kenda puncture-resistant for a little 24" BMX bike so it should be fun to take that out for a spin. And I finished a 21-speed recable job - funny, it takes the right one of the front-shifters ie. SRAM MRX Comp, Comp 2.0, or Comp 3.0, or you get the wrong gear ratios and wind up skipping some gears. So I swapped out my Comp 3.0 which is about twice as far per gear for Comp 1.0 and the bike works fine.

    Here's my flickr:
    http://www.flickr.com/photos/frankyguitarwatson/sets/72157632328268591/

    I don't know whether or not the Roadmaster has even been looked at by me in almost 3 years - I'll have to take another look at the problem that caused me to start this thread. I have so many bikes that some of them get short-shrift. :D
     
  9. offrdmania

    offrdmania Frickle Frack

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    Double check that your rear derailer mount isnt bent in. I had a bike where the derailer was rubbing the spokes, turns out the aluminum mount was bent inward. New mount = No rub. BTW, holy thread resurrection!
     
  10. PellConq1

    PellConq1 Member

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    Will do!

    I actually just resurrected the bike for a trip to the store - the valves were way crooked so I deflated the tires, straightened the valves and pumped it up. All I can say is it shifts really nicely through all of it's gears - it's just not a real fast bike so the gears do look funny (chain is a bit long I think) but it's more the ride I need to analyze - why isn't it a really fast bike? Need to check this out - could be a rub - at least I got my grocery shopping done.
     
    Last edited: Sep 15, 2013