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High and low screws front derailleur

Old 04-23-21, 03:24 PM
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cajunpedaler
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High and low screws front derailleur


Which is high and low set screws?
Are they always the same? What am I looking for to know the logic behind the physics?
thanks
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Old 04-23-21, 03:29 PM
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cxwrench
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That's so old I don't remember. Look at it from the back and it should be obvious. No, it's not always the same. 'Normal' high clamp derailleurs (Shimano mostly) have the high screw on the outboard side, low on the inboard side. The 'top swing/low clamp' (cheap) derailleurs are opposite. SRAM can be similar, or have the screws in a vertical orientation, not horizontal.
You should be able to just take a look and maybe test twist a screw and figure it out very easily.
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Old 04-23-21, 03:40 PM
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Originally Posted by cxwrench View Post
...should be able to just take a look and maybe test twist a screw and figure it out very easily.
I find it odd that they are all buggered up. Once I get my front derailuer set I mostly never have to touch it again...
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Old 04-23-21, 03:52 PM
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The photo makes them look buggered. Theyíre not really.
This is an old derailleur that Iím moving to this bike.
I also think Iím going to have to change the bottom bracket to be a tad closer in.
Thanks.
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Old 04-23-21, 04:10 PM
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To help avoid stripping the screw heads or threads, take the pressure off of the screw and then adjust it rather than trying to use the screw to drive against the spring. Also, with the shift cable disconnected the derailleur will be sitting against the low limit screw; look in the back side to see.
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Old 04-23-21, 04:16 PM
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Since the cable isn't fastened. I'd assume it will be against the low stop with spring pressure. Which screw moves it? That one is your low.
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Old 04-23-21, 04:45 PM
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Originally Posted by Iride01 View Post
Since the cable isn't fastened. I'd assume it will be against the low stop with spring pressure. Which screw moves it? That one is your low.
And you can also pull the cage out and see which one it stops against. Which would be the high.

John
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Old 04-23-21, 05:48 PM
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Originally Posted by 70sSanO View Post
And you can also pull the cage out and see which one it stops against. Which would be the high.

John
Or disconnect the cable and let the spring pull it in. That would be low. Different derailleurs position the screws differently. I think it has to do with the lever pulled down on the right side, or pulled up on the left side.
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Old 04-23-21, 06:46 PM
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With a "cold install", I do it this way.
Place chain on a larger ring.
Physically push the DER toward a larger ring to relieve pressure and turn any screw in a couple turns.
Does it return to where it was? IF NOT, you have the L screw.
IF it does, give it 1 more turn and repeat. That should be enough unless you have a mismatched crank/BB spindle length.
Return the 1st screw to about where it was and try again on the 2nd screw.

I like to set the L to where it shifts reliably every time + about 1/8 turn.
You don't want to use the L screw as a "jacking screw" to force the cage over. That wears out the threads in the DER body very quickly. Hold the cage over to relieve pressure when turning the screw.
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Old 04-23-21, 08:15 PM
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I believe that the upper screw is the low limit. As the parallelogram link whose pivot, in inside the body, rotates towards the frame it's tab will rotate away from the frame and contact the screw that's above the pivot point. Andy
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Old 04-23-21, 09:38 PM
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Looking again, I see it's a Suntour.
I don't know if/when they changed, but early (like on a 72 Takara 2x5) they were a HIGH NORMAL, which is opposite of "most" FDER's.
IF so, that would make my instructions backwards.
It looks like if you just observed it from various angles while moving the cage, it should be apparent.
It only takes 2 minutes to remove and inspect closely.
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Old 04-23-21, 10:09 PM
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Originally Posted by dsbrantjr View Post
To help avoid stripping the screw heads or threads, take the pressure off of the screw and then adjust it rather than trying to use the screw to drive against the spring. Also, with the shift cable disconnected the derailleur will be sitting against the low limit screw; look in the back side to see.
And use a JIS screw driver.
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Old 04-23-21, 10:19 PM
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Originally Posted by Bill Kapaun View Post
Looking again, I see it's a Suntour.
I don't know if/when they changed, but early (like on a 72 Takara 2x5) they were a HIGH NORMAL, which is opposite of "most" FDER's.
IF so, that would make my instructions backwards.
It looks like if you just observed it from various angles while moving the cage, it should be apparent.
It only takes 2 minutes to remove and inspect closely.
Suntour only made a few high normal front derailers. I donít think the XC Pro wasnít one of them...unfortunately. While Rapid Rise was as dumb as a bag of hammers, high normal fronts made a whole lot more sense. Downshifting while climbing with a ďregularĒ derailer can be hit or miss. Using the cable to pull the chain to a lower gear makes for an easier shift.
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Old 04-24-21, 05:36 AM
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Originally Posted by cyccommute View Post
And use a JIS screw driver.
Do you know off hand which number JIS to use for these?
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Old 04-24-21, 08:55 AM
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Originally Posted by John Nolan View Post
Do you know off hand which number JIS to use for these?
I only have one size and Iím pretty sure itís a number 2. It does work well on derailer screws. Itís kind of weird but I can really feel the difference in the way that the bit engages the screw.
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Old 04-24-21, 08:58 AM
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Thanks, I'll hunt around and see if I have a #2....I think I only have the tiny ones for cameras and the like.
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Old 04-24-21, 09:04 AM
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Yes, it's a #2. Vessel makes some really nice ones, they are what Shimano use for their 'official' JIS screwdriver.
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