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  1. #1
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    unknown problems with my mountain bike.

    Hi all
    I am new to the forums so please be gentle with me :-)
    I am having a few problems with my two mountain bikes that I can't seem to figure out.
    the first bike has been suffering with a stiff bottom bracket/front crank after several rides on a muddy gritty track (the longdendale trail if anyone wants to know) I made sure the bike was clean after every use. I came to use the bike one day last week and the front crank was stiff and there was a loud grinding noise when moving it in either direction, which I thought could be caused by grit, dirt or maybe water in the bottom bracket which would need to be re greased or replaced all together, also I thought the free wheel maybe stiff too. before taking it to a bike shop to have it looked at and fixed, I decided to check it over myself first to see if I could spot any other problems.
    I turned the bike upside down to check the rear wheel and left it like that overnight. on checking the bike in the morning, there were black water marks running down from the front crank towards the seat and it was no longer stiff, has the problem sorted itself out or would I still be better taking it to a bike shop to be looked at? also the free wheel still feels a it stiff and the front crank isn't as free moving as I am guessing it should be, any ideas?
    I also have a problem on the same bike with the front suspension (coil spring, none adjustable) sticking, it doesn't sound like there is anything stuck in the forks. any ideas on what this could be caused by and how to fix it?

    I also had a problem with the front and rear wheel on my other mountain bike, if you lift the bike off the ground by the seat and spin the rear wheel, it causes the bike to bounce, I have checked the wheel and there is no side to side movement and the wheel isn't buckled in any way that I can see, the brake pads hit the same place on the wheel rim all the way round without rubbing or catching on the tyre, no idea what could be causing this.
    also the front wheel seems to be out of balance if that is possible, same as the rear wheel, it isn't buckled, it doesn't wobble and the brake pads don't catch on the wheel rim or the tyre. but if you turn the bike upside down and pin the front wheel, as it slows down it looks like there is a weight in the wheel, just before it is about to stop, it swings like a pendulum until it finally comes to a stop, again, I have no idea what could be causing this.
    I also had a problem with the front suspension on this bike, I haven't been on it for about a week, as with my other bike I had washed it after it was last used, when I did ride it yesterday, the front suspension was stiff and wouldn't move (coil spring, adjustable) after my ride and after I had washed the bike, the suspension worked fine, is this a problem, what could it be?

    I hope I have been able to explain things properly, any advice or help you can offer me would be greatly appreciated.

    many thanks

    Paul

  2. #2
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    Quote Originally Posted by bezzer View Post
    I also had a problem with the front and rear wheel on my other mountain bike, if you lift the bike off the ground by the seat and spin the rear wheel, it causes the bike to bounce, ...also the front wheel seems to be out of balance if that is possible, ..if you turn the bike upside down and pin the front wheel, as it slows down it looks like there is a weight in the wheel, just before it is about to stop, it swings like a pendulum until it finally comes to a stop, again,
    Bicycle wheels aren't balanced the way car wheels are, at the rate they turn, they don't need to be. Rims start out as flat lengths thatn gets rolled into hoops. Many use a set of pins to strengthen the joint, which makes that part of the rim heavier than the rest.

    If it upsets you, it's possible to balance wheels. Just don't expect to notice any real life improvement when riding.

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    that could explain the problem with the front wheel, the pendulum motion on the front wheel isn't the same on the rear, but when the rear wheel is spinning it causes the bike to bounce.
    I have no idea why.

  4. #4
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by bezzer View Post
    that could explain the problem with the front wheel, the pendulum motion on the front wheel isn't the same on the rear, but when the rear wheel is spinning it causes the bike to bounce.
    I have no idea why.
    Is it bouncing while you ride? If so, you may have water trapped in the inner tube from a poorly-maintained compressor. If it's bouncing on the work stand, you're goofing off. Spinning a wheel on the stand doesn't tell you any useful information. Take the bike down and go ride.
    Jeff Wills

    All my bikes.

  5. #5
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by bezzer View Post
    that could explain the problem with the front wheel, the pendulum motion on the front wheel isn't the same on the rear, but when the rear wheel is spinning it causes the bike to bounce.
    I have no idea why.
    There may be more weight imbalance on the rear-wheel. Perhaps someone pumped in a whole bottle of Slime in the past. Anyway, imbalances aren't a big issue. While 10-20gm imbalance may bounce a 3-lbs wheel that's upside down, when you load it up with +20lb of bike and +150lb of rider in normal use, you won't be able to notice it. Especially at the low-RPMs that a bike wheel spins.

  6. #6
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    yeah I can feel it bouncing slightly when riding, I don't use a compressor and it rcently had new tyres and innertubes.
    I checked the wheels and I didn't notice anything wrong.
    I don't have the same problem with my other mountain bike.

  7. #7
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by bezzer View Post
    yeah I can feel it bouncing slightly when riding, I don't use a compressor and it rcently had new tyres and innertubes.
    I checked the wheels and I didn't notice anything wrong.
    I don't have the same problem with my other mountain bike.
    Is the tyre mounted evenly on the rim? Do the rims spin true without hops? What you are feeling may be more due to out-of-roundness than weight-imbalances (unless there's a severe imbalance, like lead-weights or rocks inside your tube). Disassemble that rear-wheel, take the tyre and tube out and inspect them carefully.

  8. #8
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    Regarding your other problems, have you ever lubed anything on the bike? Perhaps the wet weather and/or over-vigorous washing removed the lube in the bottom bracket, chain, shocks, etc. I'd certainly take it to a shop that can judge things.
    You might also list what model bikes you're talking about to give us some idea of what's on them and how cost-effective various procedures might be.

  9. #9
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    to Danno
    the rim is mounted correctly and the rims spin fine, by the wheel being out of roundness, do you mean as if the wheel had been squashed flat slightly? and if that was the case, wouldn't my brakepads rub on the tyres or would the miss shaped wheel cause the tyre to rub on another part of the frame?

    to mondoman
    I haven't had the bike for very long and I wouldn't really know how to do that, I would prefer to trust a shop with it.
    the bike with the stiff bottom bracket is a diamondback M05 and the other is a barracuda cayman.

    thanks to all for your replies.

  10. #10
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by bezzer View Post
    to Danno
    the rim is mounted correctly and the rims spin fine, by the wheel being out of roundness, do you mean as if the wheel had been squashed flat slightly? and if that was the case, wouldn't my brakepads rub on the tyres or would the miss shaped wheel cause the tyre to rub on another part of the frame?
    A wheel can be out-of-true in two different directions. It can be true laterally (axially) with no side-to-side variations, in which case, it won't rub on the brakes. But it can still be out-of-true vertically (radially) and have hops up and down. The rim is not concentric with the hub. Take the tyre off the wheel and re-mount it in the frame. Then use the brake-pads as guides and spin the wheel. Look vertically down between the pads and rim to check for lateral trueness. Then look sideways at the pads & rim to check for vertical trueness. Typically a wheel is considered "good enough" when it's +/- 0.2-0.3mm from perfect. Many wheels leave the factory at +/- 0.1mm.

    If the wheels are perfectly round and spins straight, and you feel hopping, it's most likely in the tyre and tube. If you squeeze the tube all around and there's no lead-weights or rocks inside, it's probably the tyre. A tyre with damaged casing fibres will have bulges that can cause hopping. Or a tyre that's not mounted properly and pinches the tube between the tyre and rim-sides can cause bulges as well. Dangerous bulges that can let the tube squeeze out and explode. Typically there's +10mm clearance between the tyre and anything that may rub against it. So it can wobble quite a bit before you hear any rubbing.
    Last edited by DannoXYZ; 10-17-10 at 03:59 PM.

  11. #11
    Senior Member BCRider's Avatar
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    Those stains you had and the fact that the BB sort of cleared itself up suggests that you got water into the BB and it may well be rusty in there. This would require a strip down to assess the situation and either a clean and lube or replacement depending on the findings.

    In the future when you wash your bike if you use a garden hose to rinse it do not set the spray to "blast" away the dirt or anything else. A strong jet of water can easily blow water in past the dust seals and contaminate the bearings behind the seals. Use the garden hose with a light "rain" style spray that is no more harsh than what you would expect to use on a delicate garden plant.

    If you ride your bikes a lot then you should learn to at least do a few of the more simple jobs on your own. Cleaning and oiling the chain is one such thing and you'll find lots of info around here on other factors such as putting a film of grease on the seatposts to avoid corrosion jamming them into the seat tube of the frame.

    And ditto on what Danno said about the tires. Other than the cheaper tires can have big wobbles in them even when they are just fine and when new. The cheaper tires just do not get made with the same sort of care as the more expensive ones. So for some tires you can expect a bit of runout on the tread face. But as already mentioned it is rare that folks can feel it unless you're doing warp factor 4 down a hill of some sort.

    Loose spokes in a wheel can create some funky feelings in the bars or saddle as well. Just for the heck of it go around the two wheels and use a screwdriver turned around and tap the handle on all the spokes and see if they at least all have a musical sort of note to them instead of just sounding dull and "thunky". If you have more than one or two that are "thunky" sounding then the wheel may be suffering from very bad spoke tensions and they may look decent enough when you spin the wheel when not loaded but under load they may be doing some very odd things.
    Last edited by BCRider; 10-17-10 at 09:02 PM.
    Model airplanes are cool too!.....

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