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Old 08-04-12, 07:17 AM   #1
lungimsam
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When limit screws don't work what do I do?

I have Ultegra derailers - front that doesn't move low or high, and rear - only moves on the high screw.

What do I do to get 'em working again?

Also, I have tried adjusting limits on a Tourney derailer, I think it was, and that showed no movement at all on either limit screw. Is this par for the course with cheaper derailers, or should they be working, too?
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Old 08-04-12, 07:38 AM   #2
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I don't know that I have ever seen a limit screw failure. Have you ever successfully adjusted limit screws. If you don't have much experience with it, read Park Tools and Sheldon Browns instructions. I am marginally experienced and still lean on their words. They never fail me.
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Old 08-04-12, 07:40 AM   #3
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Limit screws only adjust how far the derailleur can move right to left on the bike. They will only show movement if the derailer is at the limit. They do not adjust or fine tune any other part of the other shifting. They are basicall just stops. Roger
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Old 08-04-12, 08:19 AM   #4
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I'd suggest that you review some articles on derailleur adjustment and familiarize yourself with what needs to be done. Follow the instructions from the beginning and do not skip any steps. Here are a couple to get you started:

http://www.parktool.com/blog/repair-...nts-derailleur
http://www.parktool.com/blog/repair-...ur-adjustments
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Old 08-04-12, 09:25 AM   #5
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I'd suggest that you review some articles on derailleur adjustment and familiarize yourself with what needs to be done. Follow the instructions from the beginning and do not skip any steps. Here are a couple to get you started:

http://www.parktool.com/blog/repair-...nts-derailleur
http://www.parktool.com/blog/repair-...ur-adjustments
That's what I think too. Limit screws, once set correctly, seldom need to be readjusted.
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Old 08-04-12, 09:40 AM   #6
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They are LIMIT screws.
Their sole function is to LIMIT how far the DER's move.

IF you use them to "PUSH" the DER's, you are going to likely wear out the threads in the DER's VERY prematurely, because they aren't designed for that.
Sounds like you may have already done that?
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Old 08-04-12, 09:41 AM   #7
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Imagine either derailleur as a car parallel parked between two others on a hill.

The two cars are like limit screws. They determine the length of the space you have to maneuver in, and can be mover to give you more or less range of travel. But moving them won't move your car. You have to do that yourself. You can put your car anyplace between either car, and if you release the brake your car will roll back until it touches the lower car.

The derailleurs are the same, the cable sets their position within the working range according to the lever position, and when the cable is slackened the derailleur (not a car anymore) will settle against the return spring limit (usually outer on the rear and inner on the front). When the cable is pulled all the way tight the derailleur will stop against the upper limit.

In most systems the return spring limit is used to set that gear position, (inner front, outer rear) with the lever detents (clicks) setting the position in all the others. In some cases the high position is full up against the upper limit, in others, just shy of it allowing a bit of overshift which then settles off the limit.
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Old 08-04-12, 11:23 AM   #8
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Imagine either derailleur as a car parallel parked between two others on a hill.

The two cars are like limit screws. They determine the length of the space you have to maneuver in, and can be mover to give you more or less range of travel. But moving them won't move your car. You have to do that yourself. You can put your car anyplace between either car, and if you release the brake your car will roll back until it touches the lower car.

The derailleurs are the same, the cable sets their position within the working range according to the lever position, and when the cable is slackened the derailleur (not a car anymore) will settle against the return spring limit (usually outer on the rear and inner on the front). When the cable is pulled all the way tight the derailleur will stop against the upper limit.

In most systems the return spring limit is used to set that gear position, (inner front, outer rear) with the lever detents (clicks) setting the position in all the others. In some cases the high position is full up against the upper limit, in others, just shy of it allowing a bit of overshift which then settles off the limit.
You are perhaps one of the most helpful people on any of many forums I frequent. I really appreciate your contributions and have learned quite a bit from you. Thanks.
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Old 08-04-12, 11:33 AM   #9
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You are perhaps one of the most helpful people on any of many forums I frequent. I really appreciate your contributions and have learned quite a bit from you. Thanks.
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Old 08-04-12, 11:57 AM   #10
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You are perhaps one of the most helpful people on any of many forums I frequent. I really appreciate your contributions and have learned quite a bit from you. Thanks.
Correct. I often enter a thread to give an answer, but notice FBinNY has replied already, so not much left to say.
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Old 08-04-12, 12:00 PM   #11
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What is happening is:
I bought the bike used, and was trying to stop the chain from dropping off the hi and low ends of the rear cogs when shifting. I adjusted the hi screw on rear derailer, and that moved the pulley in line with the cog perfectly. Problem solved on that end.
But the low screw doesn't seem to do anything.
Same on hi and Low with the front derailer. The gap between the edge of the cage on either side of the rings is big and I was trying to fine tune it, but the screws don't seem to move anything when turned in either direction.
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Old 08-04-12, 12:02 PM   #12
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Correct. I often enter a thread to give an answer, but notice FBinNY has replied already, so not much left to say.
The converse is also true. In this spirit I have a short list of folks who's posts I respect highly.

They include (but aren't limited to) Hillrider, MechBgon, mrrabbit, Homebrew and Retro Grouch, We don't always agree, but that doesn't affect the respect I have for these guys.
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Old 08-04-12, 12:57 PM   #13
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The only possibility I can think of is that the original limit screws were removed and replaced with shorter ones - perhaps to save weight , or maybe someone ground the stops off the inside of the derailleur body (unlikely)

I think a more likely explanation is you are not adjusting what you think you are- either using the wrong screw, not turning it the right way, or not turning it in far enough. The function of limit screws is very simple and if you look inside the derailleur body you can see what they are doing when they come into play.
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Old 08-04-12, 01:17 PM   #14
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What is happening is:
I bought the bike used, and was trying to stop the chain from dropping off the hi and low ends of the rear cogs when shifting. I adjusted the hi screw on rear derailer, and that moved the pulley in line with the cog perfectly. Problem solved on that end.
But the low screw doesn't seem to do anything.
Same on hi and Low with the front derailer. The gap between the edge of the cage on either side of the rings is big and I was trying to fine tune it, but the screws don't seem to move anything when turned in either direction.
You shouldn't really see anything move while adjusting the screw. The effect is that when you shift, the derailleur will now move more (or less) depending on which way you turned the screw.
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Old 08-04-12, 01:21 PM   #15
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You shouldn't really see anything move while adjusting the screw. The effect is that when you shift, the derailleur will now move more (or less) depending on which way you turned the screw.
As far as I know, you should be able to see movement so that you can line up the pulley with the inner or outer cog, whichever limit you are adjusting for.
I could see the rear derailer pulley moving with every turn of the "H" screw that worked, so that I could line it up easily with the cog. I can turn the other three (the "L" on the rear derailer, and the "h" and "L" on the front derailer) in any direction down or back, with no movement.

Last edited by lungimsam; 08-04-12 at 01:26 PM.
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Old 08-04-12, 01:23 PM   #16
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Old 08-04-12, 01:24 PM   #17
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The only possibility I can think of is that the original limit screws were removed and replaced with shorter ones - perhaps to save weight , or maybe someone ground the stops off the inside of the derailleur body (unlikely)

I think a more likely explanation is you are not adjusting what you think you are- either using the wrong screw, not turning it the right way, or not turning it in far enough. The function of limit screws is very simple and if you look inside the derailleur body you can see what they are doing when they come into play.
I will try to look inside to see if the screws are contacting anything.
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Old 08-04-12, 01:34 PM   #18
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As far as I know, you should be able to see movement so that you can line up the pulley with the inner or outer cog, whichever limit you are adjusting for.
I could see the rear derailer pulley moving with every turn of the "H" screw that worked, so that I could line it up easily with the cog. I can turn the other three (the "L" on the rear derailer, and the "h" and "L" on the front derailer) in any direction down or back, with no movement.
In that instance, you saw movement because the 'H' screw was touching the tab on the RD and forcing it inward. If the screw is not contacting the tab when you turn it, or you are turning counter-clockwise to allow more movement, it won't move the derailleur because the screw is going away from the tab. I'm not a fan of having contact and forcing the derailleur to move. I prefer to turn the limit screw while not in contact, test the shifting, and repeat until it's good.
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Old 08-04-12, 01:57 PM   #19
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In that instance, you saw movement because the 'H' screw was touching the tab on the RD and forcing it inward. If the screw is not contacting the tab when you turn it, or you are turning counter-clockwise to allow more movement, it won't move the derailleur because the screw is going away from the tab. I'm not a fan of having contact and forcing the derailleur to move. I prefer to turn the limit screw while not in contact, test the shifting, and repeat until it's good.
Ah, OK, I see what you mean now.
All this helps me to understand how these things work, so I can know what I am doing better.
Thanks.
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Old 08-04-12, 02:18 PM   #20
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If you use the Park Tool procedure recommended above, you do not use the rear limit screws to "line up" the chain and pulleys, but to adjust them just loosely enough to allow for correct shifting function and no more. Visual alignment is irrelevant and can be misleading.

Another erromeous concept is that the barrel adjusters change the shift wire tension. This is incorrect; the tension is set (almost entirely) by the derailleur return spring and the adjusters change the effective wire length by changing the housing length thereby moving the derailleur position relative to a given shifter position.
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Old 08-04-12, 10:59 PM   #21
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I will try to look inside to see if the screws are contacting anything.
One more possibility is that the threads in either the derailleur or the limit screws are stripped.
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