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Discussion Starter · #1 ·
So actually, this thread consists of two questions (and could possibly be classified as a beginners post):

1) if I find a thread that has to do with this but doesn't answer my question, should I post my issue there or just start a new thread? (see post here: http://forums.mtbr.com/showthread.php?t=517445)

2) My bottom bracket wobbles slightly. A noob is me, and I only recently came to the realisation that it's the reason I get sporadic chain rub on the front derailleur when I'm riding in "bad" gears (big-big, small-small), although I get it to be the loudest when I'm in my second front crank and "gear 6" in the rear -- I've got 8 in the back, but 6 does the sporadic rub, while 7 and 8 rub constantly. I don't actually feel the wobble while pedaling, but it's plainly obvious when I'm cleaning/re-lubing/spinning the chain.

I don't use the bike very strenuously (aside from going up paved hills and an occasional curb-hop), so is this something I should get looked at? I've put about 1500-2000 miles on it like this over the past three years, so I haven't ruined anything, have I? :eek:
 

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Pretty in Pink
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What style bottom bracket do you have? Do you hear creaking or snapping when peddling under load?
 

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Discussion Starter · #3 ·
ThePinkBarron said:
Do you hear creaking or snapping when peddling under load?
No, no sounds. The only way I knew something was off was from the chain rubbing the front derailleur in certain gear setups.

What style bottom bracket do you have?
No clue... sorry. I assume it's Shimano something, but I know there's like... uh, casings and uh, open brackets? Okay, so I really have no clue. Could I send pictures to help, or could you provide things to look for so I can identify the difference? (Seriously, I'm very noob when it comes to this. Sorry.)
 

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Pictures would be good, but if you'd at least tell the brand and model of bike, we can look it up on BikePedia.

If you bottom bracket is wobbling, it's either really loose or you have a bent spindle. Hmm... another possibility is a bent chainring. Does it "wobble" regardless of chainring or does it only wobble on one particular ring?
 

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~Disc~Golf~
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can you actually feel the BB move when if you grip the crank by hand and pull back and forth?
 

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Discussion Starter · #7 ·
Ah, sorry for lack of details. It's a shimano crank (and bottom bracket I'd assume), but that's all I know. I bought the bike in July '05, and honestly, that's about all the details I can give you.

Does it "wobble" regardless of chainring
I've only noticed it on the second and first, not on the largest. and only when I am in a bad gear combo. But the entire set of chain rings and the guard thing on the outside have a visible (albeit slight) wobble.

can you actually feel the BB move when if you grip the crank by hand and pull back and forth?
No, it's solid.


 

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~Disc~Golf~
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OK, you have a sealed cartridge square-taper BB - I would guess a BB-UN53 or 54 (and, yes, Shimano) - or worse a BB-UN26 :eek: (you can tell if it's the 26 if you pull-out the bolts and you can't see through, ie. solid - not hollow)

My guess is that either:
a) you have a slightly loose crank - you can try to remedy that first by tightening that bolt down w/ a 15mm socket.(might as well do both)
If it's been loose for a while you may have a worn crank at the spindle interface - if that's the case you're lookin at a new set of crank arms.
b) The spindle is bent - shift your chain to the smallest ring, then manually drop it off onto the BB shell, next look carefully at all your rings as you spin the crank - if they wobble/ oscillate - new BB ~$20 for your current model IIRC, but might as well upgrade to a BB-UN72 or something - I think they're ~$35?
c) bearing is shot or spindle is flexing - upgrade to BB-UN72

you'll need a crank-puller (~$15) to pull the cranks
and a BB tool to change the BB (also ~$ 15)
your LBS should be able to hook you up with all of that -

My guess is 'B', but check those suggestions in order to isolate
 

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Discussion Starter · #10 · (Edited)
scoutcat said:
u just need to adjust your front derailleur. try turning the barrel adjuster a half turn
Mkay... I just took off/cleaned/put back on both derailleurs, so I could understand how they could be out of whack. Unfortunately, that doesn't have anything to do with my cranks wobbling. (I checked it out... my gears shift fine. I ain't touching anything until I'm unhappy with them again.)

OK, you have a sealed cartridge square-taper BB
I'll keep that in mind. Means nothing to me, unfortunately.

My guess is that either:
a) you have a slightly loose crank
Nah, I'm pretty sure this isn't the case. I tried taking the cranks off about three months ago, not knowing that whole area doesn't come apart without special tools. Everything seemed to be screwed in there quite well.

b) The spindle is bent [...] new BB ~$20 for your current model IIRC, but might as well upgrade to a BB-UN72 or something - I think they're ~$35?
Well, that's not too shabby. Would this be something I'd just have to have the LBS people do? Or would you recommend I just get a crank puller and bottom bracket tool and figure it out myself? (I see that you mention it, so it's got to be at least a slim possibility... :))

EDIT: My husband just pointed out that we got the bike in '06, not '05. Dunno if that makes a difference, but figured I'd correct it anyway.
 

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~Disc~Golf~
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Kelly Mo said:
... Would this be something I'd just have to have the LBS people do? Or would you recommend I just get a crank puller and bottom bracket tool and figure it out myself? (I see that you mention it, so it's got to be at least a slim possibility... :))

EDIT: My husband just pointed out that we got the bike in '06, not '05. Dunno if that makes a difference, but figured I'd correct it anyway.
You could have the LBS do it, but I find working on your bike much more rewarding - plus you'll have the tools for later AND it's dead-simple to pull cranks and do the BB.

It doesn't matter what year it is - I'm goin off of your pics - I've seen a few of those :D

I know you said it's evident that there's a wobble, but just to satisfy others suggesting to double check w/ bad gear combos - double check before any purchase -
feel free to PM me or post again for more help :thumbsup:
 

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Pretty in Pink
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Those arent cages on your pedals are they? Please remove those pronto.
 

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Discussion Starter · #14 ·
ThePinkBarron said:
Those arent cages on your pedals are they? Please remove those pronto.
Yes they are. No I won't. Cuz after that what's to stop you from making fun of the flower basket on the front, and then what next? No more handlebar tassels? :cryin: Sorry, this is how I roll... til I get new pedals.

As for the BB:
I think I'll try doing it myself. Unfortunately, I need to wait til the hubby gets home to find out where he hid the crank puller, and soon after we're flying home for about a month. So I'll probably get to it some time in August. That'd also allow us to pick up the parts in the States, where things are a bit cheaper overall anyway.
 

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Pretty in Pink
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Kelly Mo said:
Yes they are. No I won't. Cuz after that what's to stop you from making fun of the flower basket on the front, and then what next? No more handlebar tassels? :cryin: Sorry, this is how I roll... til I get new pedals.

As for the BB:
I think I'll try doing it myself. Unfortunately, I need to wait til the hubby gets home to find out where he hid the crank puller, and soon after we're flying home for about a month. So I'll probably get to it some time in August. That'd also allow us to pick up the parts in the States, where things are a bit cheaper overall anyway.
I will send you some free SPD style clipless pedals if you remove the cages. Those things are just asking for an accident.

You can keep the handlebar tassels that is just stylish.
 

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Discussion Starter · #16 ·
Haha, thanks for the offer, but I rarely do anything anywhere near dangerous on this bike. It's been a touring bike and is currently unused. I plan to make it back into a proper mtb towards the end of this summer (when the weather's too crappy to ride the road bike), possibly something for snow/heavy rain (but no off-roading) use.
 
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