Bicycle Mechanics - Front derailer: can't get it right (tonnes of photos)
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07-30-09, 04:14 PM
My first thread here; I've spent 8 hours over the past two days trying to get my front derailer right! I would take it into my LBS, but I'm going touring (2000 miles inc. mountains) on this bike so I should really learn how to fix it.
Firstly, there's a reasonable amount of rattling in the system when the system is set up roughly right and the 3rd gear (at the front) is being used. Here's a video: video on flickr (http://www.flickr.com/photos/30731707@N02/3773283924/). If that is the problem then please let me know although I'm not convinced it is because even holding it still I cant get them to work.
A bit of basic info:
I define working as 1:1-3, 2:1-8, and 3:6-8 working without grinding the derailer well after I have shifted
The bike is a decathlon rockrider 5.3
Its done just over 10,000 miles, and has had all the cogs and the chain replaced, and possibly the derailers about 2 years ago (since then it hasn't done many miles)
I think it used to work, but I was adjusting this because the derailers were grinding against the chain in some gears
Chainset: 8 cogs
Front: 3 cogs
Derailer: Shimano (says chainstay angle 66-69 on it)
Bike is upside down, so all pictures are taken as such
Photos of my setup (because i dont know all the names) [Links let you view different sizes]
(dogey cable from adjusting so much, i did this same technique when it worked)
Ok heres what I have done to adjust it:
1. Set the angle so that the (imagined) centreline is parallel to the cogs, and height is such that the outer side of the derailer just clears the outer cog:
...continued in next post to add more images :)
07-30-09, 04:17 PM
2. Set the lower limit screw so that the inner part of the derailer just clears the chain when set in 1:1.[/B]
Other angles also after adjustment:
3. Set the high limit screw so that the outer part of the derailer just clears the chain when set in 3:8. I pushed the front derailer out as far as it could go to do this with my thumb
Clearance this gives when pushed as far as it can go:
4. Put in 1:1 and tense up the cable to take out slack, then tighten to hold cable there.
1:1 clears by quite a bit
2:1 clears by quite a bit
Things I've tried:
Combinations and individually of moving the derailer up and down on the frame, pivoting it, tensioning the gear cable slightly more so it only just clears on 1:1, adjusting limiters again.
Whatever I do it doesn't seem to work, and the thing itself feels so strong I cant bend it so I dont think its bent but I guess it might be.
Help please! Anything would be very much appreciated.
07-30-09, 04:23 PM
You're making me sea-sick! Anywho - here is my cut & paste fix-all for FD complaints:
Take the cable off the FD. Now install it from scratch as per Park Tool Repair:
When you have it properly trimmed and are ready for the cable - a new one wouldn't hurt - you want to pull the cable taut - not too tight, taut. Then apply 48 to 60 inch-pounds to the pinch-bolt. Then put it through it's paces.
It's always easier and faster to install a FD from square-one, than it is to make adjustments with it already attached. This tends to fix one thing - while throwing another out of kilter. Start fresh. You'll get it.
Adding a barrel-adjuster can solve many problems with the cable coming loose - or being too tight.
07-30-09, 04:27 PM
I was using that bicycle tutor video to start from scratch (as outlined above), and sorry about the mass of slightly blurred images! I'll take your advice about getting a new cable as well when I've got this sorted. Thanks
07-30-09, 07:08 PM
I think also your standards for chain rub might be a bit high. With many of the Shimano setups particularly on those with cheaper shifters and front derailleurs, there is no way to achieve zero rubbing in the gear combinations you listed above. On road bikes, they've made it even more troublesome by now manufacturing only left shifters that are both double and triple, and do neither as well as they should.
In my experience, the largest trick is getting the initial cable tension correct. In some cases, I have had to tighten the limiting screw until the der cage was firlmly pressing on the chain in the small ring before pulling the cable tight and tightening it to the front derailleur. I then loosen the limiting screw back to the proper place, but the cable tension is now correct.
It takes multiple attempts and patience. I don't envy you.
07-30-09, 07:39 PM
Fair enough, that makes a lot of sense. I'll just get it as good as I can then (after a replaced cable). Thinking about it, its only now I'm touring that I use the easier gears so it probably was always like this.
Thanks for having a look!
07-30-09, 09:51 PM
ac - thanks for posting lots of detailed photos!
You may also want to consider buying a new FD, as they are usually fairly cheap, with decent midrange ones (at least for mountain bikes) available in the $20 range if you shop around.
As others have suggested, you should really replace both gear cables and both brake cables and their housings before your trip; total cost should be in the $20-30 range if you shop wisely. As an added bonus, that will teach you how to adjust the FD, RD, and brakes, skills that should come in very handy on your tour!
07-30-09, 09:59 PM
Use the Macro function on your camera
With the level of components you have, its pretty impossible to get no rubbing in all combinations. You just have to deal with it
07-30-09, 10:09 PM
I cant quite see clearly what I want to comment on but the very first thing you need to do with a front derailer is to make sure its bolted on as low as possible without hitting the chainrings. If its 3-4mm higher than it could be then its VERY difficult to get it performing correctly. Its also important to get its alignment correct. No amount of cable and stop adjustment is going to correct a derailer thats not bolted onto the seat tube with the correct alignment.
07-31-09, 03:21 AM
Thanks everyone, will a new front derailer be necessary to keep the system reliable for this trip? I want to slowly upgrade to a good quality tourer anyway, but given that this is my longest tour by far I feel like I should wait to see what I find I need most.
Also I'll get those cables and tubing spares; there's 5 bikes on the trip so I'm sure alot of these will break.
AnthonyG - I think it may be the angle of the photo; its got about a 1-2mm clearance over the 3rd gear.
07-31-09, 03:41 AM
Half of those photos were upside-down! Lordy!
You want a FD (front der.)? Then learn what we are trying to help you learn: Proper installation. I'd suggest installing a barrel-adjuster to maintain proper cable-tension once you have it properly installed and working correctly. Instead of releasing the pinch-bolt, tugging the cable again, and re-torquing the pinch-bolt - just twist the BA. Cables do settle (stretch) which will (WILL) throw the adjustment off.
If you don't want a FD - remove it. You'll have 1/2 as many gears as you could have. Going touring in mountainous terrain? And you wonder if you need an FD? Ridiculous! I'm starting to smell 'troll.'
Lastly - I leave you with a photo of a BA (barrel-adjuster) mounted on a FD cable:
07-31-09, 05:05 AM
Sorry I meant do I need a new derailer to keep things reliable, as opposed to sticking with the one I currently have. I'm aware the variety of gears will be very useful on this trip.
07-31-09, 06:59 AM
Your derailleur looks very high
07-31-09, 09:40 AM
stop bitting your fingernails
07-31-09, 10:42 AM
Here's a basic setup question: Is your rear wheel lined up correctly? My shopping bicycle suddenly developed some shifting issues. I was scratching my head when I noticed that the back wheel wasn't quite straight in the dropouts. That's probably not your problem, but it's always good to check for the basic stuff.
07-31-09, 01:34 PM
Your definition of "reliable" needs to be modified. If the derailleur will shift to all three chainrings, it's reliable and fully functional. Rubbing the chain on the cage is a secondary annoyance that's not in any way related to reliability. There's a process called "trimming" where you make minor movements to the FD position to prevent rubbing, but not so much movement that it shifts the chain. This is the way a front-derailleur works for 99.99% of the bikes out there. You'll be hard-pressed to find one that works without trimming needed to prevent noise.
As already posted, the Park Tool site is the most helpful in FD adjustments. You CANNOT skip steps, the FD physical height and rotation must be set optimally first or else ALL OTHER adjustments will be insignificant. So first, the height MUST be as close to the chainrings as possible; yours look a little too high:
The curvature of the cage also doesn't match the chainrings, you may need an FD designed for smaller chainrings.
Then the ROTATION must be optimized to the chain. Most shops teach their employees to align the FD-cage with the chainrings in order to get consistent results, however, it gives you consistently mediocre results, but at least all the bikes leaving the shop will perform the same. You want to align the outer cage with the CHAIN when set in the highest gears:
Once you've got these two adjustments done, everything else will be easier and you may actually be able to dial it in so it doesn't rub. I find uncrewing the rear of the cage and inserting a spacer with longer bolt so that the shape is more of a trapezoid really helps prevent chain-rubbing. That's because the path of the chain flares out towards the back as it sweeps across the cluster, so you want the FD-cage to be shaped more like a bird's tail with flared out back to match the chain's lateral sweep. Some Shimano derailleurs have his feature with a cage that flares out in the rear.
The 3rd most-critical adjustment is CABLE-TENSION. This affects the position of the FD when it's over the middle-chainring. There's ABSOLUTELY ZERO adjustments you can make with the limit-screws that'll affect the FD position when it's over the middle-ring and this the most critical gear because you're trying to sweep the chain across all 8-gears in back. So use the cable-tension to optimize the FD position in the middle-chainring FIRST. Most shifters have a barrel-adjuster somewhere between the shifter and FD; usually on the shifter itself. If not, you MUST get the inline cable-tension adjuster pictured above to make fine-adjustments to cable-tension to fine-tune the middle-chainring position.
Then final and least-significant adjustment is to set the limit screws to work in the big and granny rings afterwards. In fact, I never set the inner-limit screw anyway. I just let the shifter determine the inner position when the lever is moved to the innermost position.
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