Author Topic: Bicycle repair help  (Read 2778 times)

Travis

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Bicycle repair help
« on: October 24, 2019, 01:18:24 AM »
I have an 18-speed bike and one of the shifting levers isn't working right.  I can go from "8" to "5" with no problem, but if I try to drop it down any further the lever swings all the way over without grabbing any more gears.  Any ideas or can you point me to a good repair website/forum?

RWD

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Re: Bicycle repair help
« Reply #1 on: October 24, 2019, 06:37:31 AM »
Maybe the derailleur needs adjustment?
https://www.youtube.com/watch?v=UkZxPIZ1ngY

lthenderson

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Re: Bicycle repair help
« Reply #2 on: October 24, 2019, 06:50:14 AM »
You need to apply more tension to your shifter cable. There should be a threaded adjustment screw of some sort where your cable enters the shifter assembly on your handlebars.

GuitarStv

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Re: Bicycle repair help
« Reply #3 on: October 24, 2019, 07:47:42 AM »
There are three adjustment points on your derailleur - a barrel adjuster, and H/L screws on your rear derailleur.  Think of H as 'hard gear' and L as 'lazy gear'.  The barrel adjuster is for fine tuning cable tension.

If the derailleur won't shift all the way down to the smallest gear, it can be one of two things:
* Incorrect H screw adjustment - To check this, unbolt the cable to your derailleur and pedal a few times.  The chain should drop to the lowest gear.  If it doesn't drop to the lowest gear, then the H screw is too tight and must be loosened until the chain drops to the lowest gear.
* Incorrect cable tension - Once you know that your H screw is set properly, just pull the slack out of the shifter cable and bolt it back on.

If the derailleur won't shift all the way up to the biggest gear, you need to adjust the L screw (that's the cog you use when you're feeling lazy).  Put the bike in the easiest gear it will go to.  Loosening the L screw and shifting up/down will allow the chain to travel further towards the spokes, tightening it will move the chain the other direction.


After you get the H and L screws set properly (so the chain can go all the way up and down the cassette) you'll probably notice a few gears that don't shift nicely.  No problem.  Put the chain on the second smallest gear and shift to the third smallest gear.  If this is slow to shift up, loosen the barrel adjuster a notch.  Then switch from the third smallest gear to the second smallest gear.  If this is slow to shift down, tighten the barrel adjuster.  Keep playing with it until you're switching seamlessly from 2-3 and 3-2.

Then you should be good.

nereo

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Re: Bicycle repair help
« Reply #4 on: October 24, 2019, 07:49:09 AM »
Sheldon Brown (google it - on a small device) is my go-to for figuring out bike repairs.  Absolute wealth of bike information.

GuitarStv gave an excellent breakdown of your specific problem.

Also - I’d highly recommend looking to see if your town/city has a bike coop.  Most universities (and many community colleges) have these, and often they are open to the public.  For a paltry fee you get access to a working space and all the bike tools you will ever need, plus (usually) a bunch of competent mechanics who will help you out if you are patient and kind.  That’s how I learned most of my bike maintenance skills.  I think I paid $25/year for unlimited use of the bike-coop and a discount on common parts (e.g. tubes, shifting cables).  They kept a stash of used parts from abandoned/donated bikes so most of the time I could fix my bike for just a couple bucks.

Travis

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Re: Bicycle repair help
« Reply #5 on: October 26, 2019, 09:19:40 PM »
I got the bike to about a 90% solution.  I worked on it for a couple hours this morning tightening and loosening the H and L screws (which aren't labeled) and experimenting with cable tension.  I don't know what I did, but just as I was about to give up in frustration it started transitioning up and down the cogs.  At the beginning I could not find any adjustment that would keep the chain on the largest cog.  The way I have it now there are a couple of the middle cogs that the system will just skip over, but it's much better than it was before. 

I watched five videos on Youtube about this and all of them assume you just need "an adjustment."  Most would start their video with "put your chain on the the largest cog and do X."  I couldn't do anything that would get the chain in that position.  The derailleur was locking out in the middle, and if I did get the chain up there, it would drop back down within a couple revolutions.

Thank you for the advice.

GuitarStv

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Re: Bicycle repair help
« Reply #6 on: October 27, 2019, 11:32:42 AM »
Sounds like you're almost there.  Just do the 2-3 and 3-2 gear thing and play with the barrel adjuster (one click at a time) until you've got it shifting perfectly.  It takes forever the first few times you tune the shifting, but after a couple dozen goes at it things speed up. 

Travis

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Re: Bicycle repair help
« Reply #7 on: October 27, 2019, 06:14:10 PM »
This barrel adjuster you and the videos keep mentioning - I have a little knob on the rear side of the cable that appears to be there to screw the cable in place.  Same thing?  It's currently turned as far as it will go. I start to loosen it and the cable feels like it might fall out of place.

GuitarStv

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Re: Bicycle repair help
« Reply #8 on: October 27, 2019, 06:29:28 PM »
This barrel adjuster you and the videos keep mentioning - I have a little knob on the rear side of the cable that appears to be there to screw the cable in place.  Same thing?  It's currently turned as far as it will go. I start to loosen it and the cable feels like it might fall out of place.



It's the thing that sticks off the derailleur and turns that the cable and cable housing goes into.  What it does is tighten the cable in very tiny increments to allow you to fine tune the shifting.

If you're out of adjustment room, you need to unbolt the cable, tighten the barrel adjuster, and then pull the cable tight and bolt it back on.  Otherwise you'll never be able to get your bike to shift properly.

Just Joe

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Re: Bicycle repair help
« Reply #9 on: October 28, 2019, 09:19:08 AM »
OP - I don't know how technically minded you are but when I'm faced with a new mechanism I spend a few minutes identifying the parts. That way if I watch a video I can focus on how they make the adjustments rather than which parts they are interacting with.

You could also have a cable that is not sliding smoothly through it's housing or guides. Might need to be removed and everything cleaned and lubed. You'll want to have a new cable end - the part that is crimped at the end that keeps the cable from fraying. Yous LBS will have them and they should be cheap. Once upon a time I bought ten from Amazon and I may have some in my toolbox until the end of my days at the rate I'm using them.

I would also consider cleaning and lubing the derailleur. I have a beater bike that has a very crusty derailleur that doesn't shift well unless it is occasionally cleaned and lubed. I mostly spray stuff and it and fail to clean it. An old Schwinn.

BikingEngineer

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Re: Bicycle repair help
« Reply #10 on: November 07, 2019, 10:02:51 AM »
Try https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment to start. If you're skipping a bunch of gears when you shift there might be something wrong with the shifter. What sort of shifting mechanism does your bike have?

Travis

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Re: Bicycle repair help
« Reply #11 on: November 08, 2019, 01:12:23 AM »
Try https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment to start. If you're skipping a bunch of gears when you shift there might be something wrong with the shifter. What sort of shifting mechanism does your bike have?

I tried that site and didn't really help.  The steps they describe aren't having an effect on my bike's symptoms. Here is a video of what it's doing: https://youtu.be/AeyhqDmkDQU.  It looks like whatever changes I made didn't stick. It's back to not having any tension for the lower gears most of the time.  When I get down to the number 5 gear and try to go any lower that thumb lever will push all the way out and won't catch the next gear.  Strangely, when the bike is just sitting still like in the video it'll catch the next gears more often whereas on the road it'll stay in the 5 position almost the entire ride.

Could something be loose or broken inside the shifter?

Travis

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Re: Bicycle repair help
« Reply #12 on: November 08, 2019, 02:18:50 AM »
Possible solution? This looks a lot like what I'm dealing with.

https://www.youtube.com/watch?v=UCRG8J35CVc

https://www.youtube.com/watch?v=0Wtb57AXD0o&t=216s
« Last Edit: November 08, 2019, 02:26:13 AM by Travis »

GuitarStv

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Re: Bicycle repair help
« Reply #13 on: November 08, 2019, 07:29:03 AM »
Could something be loose or broken inside the shifter?

Could be.

I'd try blasting the internals with some WD-40 to see if it's gummed up from dried lubricant though before tossing it.


EDIT - yeah, that seems to be what the videos you're posting suggest.  I've never taken apart one of those shifters to try and clean it, so don't know how complicated that procedure is.  With modern road bike STI shifters it's VERY VERY complicated - enough that I wouldn't bother.

salty_monk

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Re: Bicycle repair help
« Reply #14 on: November 14, 2019, 01:19:57 PM »
Springs will ping everywhere & it will be impossible to re-assemble.... ask me how I know :lol:

Easy and cheap enough to find a replacement on Amazon or Ebay. :)

 

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