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front derailleur adjustments - I'm so ashamed

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front derailleur adjustments - I'm so ashamed

Old 08-05-14, 06:23 PM
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schlopartist
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front derailleur adjustments - I'm so ashamed

Dirty Harry in "Magnum Force" says, "a man has got to know his limitations".

Today, I acknowledge one. For years I tried to adjusting that 24yr old Shimano front derailleur and STILL could not keep the chain from rubbing. So much so that the cable frayed. (10yr cable crushed and broken) Today, I called uncle and took it to a bike shop for new cables all round and proper adjustments.

What am I doing wrong!
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Old 08-05-14, 06:57 PM
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On most bike the chain will rub the front derailleur if you do not "trim" (micro-shift) as you ride.

As you shift the rear derailleur from easiest to hardest (inboard to outboard), the chain moves also. At some point it will start rubbing the front derailleur. That's when you shift the front a tiny bit to stop the rubbing.

Short version: They all do that.

The above assumes that front & rear are shifting fine other than occasional front rubbing.
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Old 08-06-14, 08:03 PM
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when was it rubbing? in all gears or just a few, if a few on the small or big cogs or chainrings. If the derailleur is clamp on theres always the possibility that it was installed at an angle, which makes adjusting the limits all but pointless
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Old 08-06-14, 08:53 PM
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24yr old? You never said whether this is an index front with a single click position, or a non-index which you hand trim by fine tuning the lever position.

Either way, you start by understanding the nature of the issue. The cage represents a slot or gate through the chain passes on the way to the sprocket. Bcause you shift in the rear, the chain comes from a range of angles.

By way of seeing this, stand outside and back from an open door, and look into the room sighting a target, say a lamp. The line of sight is your chain. Now move to either side, and eventually the door frame will block the target from your sight, the same way the side of the cage will rub.

So the key is to adjust the FD so you can move the slot according to the angle the chain is coming from, so as to maintain "line of sight" at all times.
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Old 08-06-14, 09:06 PM
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But how do you move the door frame ?
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Old 08-06-14, 09:23 PM
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Originally Posted by Homebrew01 View Post
But how do you move the door frame ?
In this analogy the door frame is the ft der cage. it moves because it's attached to a parallelogram device that is distorted by a cable. One side of this parallelogram is fixed onto the seat tube, the opposite side is attached to the cage.

Oh, you were fooling Andy.
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Old 08-06-14, 10:00 PM
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Originally Posted by Andrew R Stewart View Post
In this analogy the door frame is the ft der cage. it moves because it's attached to a parallelogram device that is distorted by a cable. One side of this parallelogram is fixed onto the seat tube, the opposite side is attached to the cage.

Oh, you were fooling Andy.
modern door frames are extensively shaped on both sides
to allow indexed hinges and triple door knobs
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Old 08-06-14, 10:11 PM
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Originally Posted by Wilfred Laurier View Post
modern door frames are extensively shaped on both sides
to allow indexed hinges and triple door knobs
Yes, but in my analogy the door frame couldn't move because it was a 1st generation Shimano index type without the trim feature.
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Old 08-08-14, 06:30 PM
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Originally Posted by FBinNY View Post
24yr old? You never said whether this is an index front with a single click position, or a non-index which you hand trim by fine tuning the lever position.
sorry about that. index, but a pic says a thousand words


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Old 08-08-14, 06:42 PM
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Originally Posted by Wythnail View Post
when was it rubbing? in all gears or just a few, if a few on the small or big cogs or chainrings. If the derailleur is clamp on theres always the possibility that it was installed at an angle, which makes adjusting the limits all but pointless
It rubbed... well actually moved around the cage at the extremes. as if was ready to change to the next gear. I can only suspect that the cable was played out. It was frayed thanks to me, but I suspect it was stretched out after 10yrs of service (time since it was replaced) and unable to hold its position any longer. The bike shop set it all right now AND with a new stem riser. She a runnin' smooth as a Swiss watch now.



'e might be old, but feels ready to ride! wha?! cheap cheap cheap... HEY! who let the bird in?
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