front deraileur repair question

JHZR2

Staff member
Messages
44,823
Location
New Jersey
Hello, I went on a short ride one day - about 10 miles - no issues. the next day, I went out to ride, and when my chain was on the middle (of three) chainrings on the front, I got a scrape every time that I pedaled around. On the small and large chainring, no worries or issues - smooth. On that middle one, scraping. I worked on it a bit tonight... The large chainring is so close to the outer bottom edge of the cage, that it scrapes with the tops of the large chainring. Ive tried adjusting the deraileur to get it better, but the thing is, it shifts well as-is. Adjust it, and it doesnt. Its almost like I need to bend the cage, or file it down... but that cannot be right. The whole assembly has play, but the bike is only 8 years and maybe 1000 miles, I cannot imagine it is worn out. Any thoughts??? Ill try to post a picture. Thanks!
 

JHZR2

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44,823
Location
New Jersey
Just too close, and I don't know how to proceed... Any recommendations? I also think the deraileur has too much play...
 
Messages
2,789
Location
California, USA
I wish I could help, but I have no experience here. But it sounds like it was not scraping one day and then the next day it was, right? That seems strange. Is there maybe some fine vertical adjustment that could've gotten knocked out of line a tad?
 
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2,695
Location
Easton, PA
 Originally Posted By: rationull
Is there maybe some fine vertical adjustment that could've gotten knocked out of line a tad?
it looks like it slipped down a little. there is a 5mm bolt holing the clamp to the frame; loosen that and move it up about a mm or 2. you have whats called a 'top swing' derailuer, yes, they have some play in them from new. setting the high and low limits (not referring to height, but how far it travels inboard and outboard) on them are a pain also. don't worry about having to bend the cage if necessary. I worked as a bike tech for 15 yrs, and I don't think there was ever a cage I DIDN'T bend/adjust/manipulate for better performance.
 

JHZR2

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Thread starter
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44,823
Location
New Jersey
Thanks! Tried moving it up, but shifting suffered. I actually had to toe it a bit... Its obvious now, but wasnt to me a few hours and days ago. Now if it would only stop raining, Id go out for 40 miles...
 
Messages
6,991
Location
Everett, Washington
Park Tool has a repair section that will walk you through the adjustment. http://www.parktool.com/repair/readhowto.asp?id=75 I had been doing all my adjustments on front and rear derailleur's all wrong over the years. My Motobecane front derailleur was way too high on the frame tube. It came from the Factory that way. All the adjustments were off on it. They show a penny or dime between the teeth and the derailleur body as part of the adjustment. Your chain looks dry/rusty from the photo. I have done adjustments on 2 bikes and the park site is just great as far as info. Good luck
 
Messages
1,050
Location
Calif.
It took me a while to get it right since you have to adjust the height first. Use a coin as a guide to set the gap between the chainring an the derailer. Then you have to center it with the chain by looking on top, it may take a few times to get it right. Good luck. Bicycle Tutor has a lot of great how to videos. Here is the link for front derailer adjustment. http://bicycletutor.com/adjust-front-derailer/
 
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Messages
10,611
Location
Las Vegas NV
From what I have seen on the web, the cage should be about 2-3mm above the big chain ring. Set that first and then check the stops. After I did this to mine, it shifted much better. It came too high from the factory.
 
Messages
404
Location
The Mid South
It looks like there's subtle scratches at the back end of the guide cage. Did it get tweaked/bent from hitting something? If so, it looks like it rotated forward a bit-extra clearance aft, rubbing forward. May have to un-tweak it, as others have suggested.
 
Messages
1,899
Location
Columbia, SC
Best way to adjust: Set the derailleur so that it is (as was said), 2 or 3 mm above the largest chainring and IN LINE with the ring. Shift into the largest gear in back and the smallest in front. Adjust the lower limit screw so that the chain falls off the ring. This is your starting point. Remount the chain and shift to the middle ring. Down shift and up shift (adjusting the limit screw) until the chain no longer drops off the small ring. Now, shift into the smallest rear and largest front combo. Adjust the upper limit screw until the chain rubs or the chain falls off outside the ring. Remount the chain and downshift and upshift (adjusting the screw) until the chain no longer drops off the pedal side. You have successfully set the limit screws. Don't mess with them anymore. Turn the barrel adjusters all the way IN. Now, go about 4 or five turns out. Loosen the bolt holding the cable to the derailleur and remove any remaining slack before re-securing the bolt. You have now reached your adjusting starting point. Small ring, small cog combo: Shift up. Smooth? Stop. Over shift? Turn the barrel adjuster in. Under shift? Turn the adjuster out. Repeat with the middle ring/big ring combo, staying in the small cog in the rear. Once you get the main shifting down, you have to fine tune the shift, using the big rear cog and smallest rear cog. If the chain hesitates its downshift, create more slack. If the chain hesitates its upshift, create more tension. It's picky and 1/8 or 1/16 twists make a difference. Most front shifters have an adjustment click. In the small ring/small cog combo you will get a rub. One click and it's gone. Same may be true for the large ring and middle ring. Hope this helps.
 
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