# Front derailleur front-to-back angle?



## ctslater (Apr 1, 2014)

Bought a used Giant OCR a little while ago, and while everything else about the bike is great, I'm stumped on trying to get the front derailleur to behave. The issue is that the rear end of the derailleur is very close to the biggest chainring and will intermittently make contact with it. However the front end of the derailleur is already several mm above the chainring, and it's about as high as it can go. I've attached a picture to try and show the angle problem.

So it looks to me like I need to adjust this front-to-back angle, but there doesn't seem to be any mechanism to do that with how it's mounted to the frame. I have no knowledge of how this bike got this way or who put what hardware on when, it's just as-is. I could only find a very few mentions of this type of problem after much googling, which included some mentions of possibly adding shims to adjust the angle, but I figured I should check that I'm not missing something obvious before I start to tear it apart. Any thoughts would be appreciated.


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## bikerjulio (Jan 19, 2010)

The mounting tab, otherwise known as "braze on" is in the wrong place. Looks like a botched repair job. A pic from the front would help to confirm.

The tab should be on the centreline of the seat tube, not at the front.

Perhaps just remove it and use a clamp instead.


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## headloss (Mar 3, 2013)

Unless it's warped/bent (or misplaced, as Julio suggests), that FD should fit a 52t ring fine. The gap under the five should be about 2mm at the most, that looks like more. The tail end _should_ clear without a problem, but if that's as far as it will go outward, then the high limit screw might also be too tight (FDs can be tricky with perception, is that out all the way?). At least, that is true for me and I have the exact same FD. 

It looks like the braze-on fd clamp is fixed/attached to the frame, so (my guess) you can't adjust the rotation. I've never seen that type of clamp, the only bike I have with a FD braze-on is welded to the tube. 

Looking at your picture, I can see why you are concerned. What is the frame angle? What is the size of that ring? Perhaps it's a bad combination of parts?


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## bikerjulio (Jan 19, 2010)

Looks like a home made tab, either screwed or pop riveted to the front of the seat tube.

Notice the absence of a slot.

It's at least 1/2" too far forward, that's why nothing lines up.

Just take it off and buy a clamp.

here is where the tab is supposed to be


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## davcruz (Oct 9, 2007)

The "braze-on" is correct for his Giant OCR 1. Giant uses that style mount on lots of frames and it should have a slot in it and since he says it is moved up as far as it can be I ma assuming it does indeed have the slot. Perhaps the hanger is bent, hard to tell from the picture but my guess is that headloss is correct and we may have a mix match of parts, like the front chain ring is too big.


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## davcruz (Oct 9, 2007)

And dang is that a big picture!!


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## bikerjulio (Jan 19, 2010)

You can clearly see that OP's tab does not have a slot.

And if that's the normal location for the bike it's still wrong.

The blue example illustrates the same problem as OP has.

It's just simple geometry. If the FD is too far forward then the rear is going to interfere with the chainring.

Surely Shimano has a standard for tab location? Where's the Shimano experts?

I still say that if the tab can be removed, then do so and replace with a standard clamp.


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## wim (Feb 28, 2005)

Not 100% sure, but I think the OCR hanger is held on with two countersunk-head screws. If yours is, make sure those screws are reasonable tight. Don't over-torque them, though. Easy does it. The lower screw in your photo looks as if it has backed out just a tad.

If the screws are long enough, you could re-angle the mounting tab easily by placing a washer between it and the frame at one of the screws.


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## ctslater (Apr 1, 2014)

Interesting, I'm glad I'm not the only one thinking it might have been installed wrong. Here's a picture from the front in case that helps. I don't have the specs on the individual components right now, but it wouldn't surprise me if it was some weird combination of parts (although it's 100% 105-everything).


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## wim (Feb 28, 2005)

Could be the wrong hanger or a bent one. It is indeed screwed on, so no problems replacing it with the correct one if the one on there now is not the right one or is bent.

With the hanger being screwed on (not pop-riveted), it's pretty unlikely that the location of the mounting holes on the seat tube are incorrect. The "105" or other parts designation has nothing to do with any of this. Hangers go with and need to match the frame.


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## bikerjulio (Jan 19, 2010)

Although I was wrong about the slot, I'm still not sure the tab location meets Shimano's standard, which I looked up.

Here Shimano Framebuilder Info - Pvdwiki it says that the mounting surface for the FD should be 8.7mm ahead of the seat tube centreline.

In OP's original picture the front edge of the FD appears to be about 2-3mm behind the front of the ST. If I guess the ST OD as 32mm, then the tab is at 16 - 3 = 13mm ahead of the C/L, and therefore 4-5mm too far forward.

Since the tab is easily removable, I'm still thinking my original suggestion is the best one. PLus it provides a bit more adjustability.


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## davcruz (Oct 9, 2007)

I have a hard time believing that Giant put the mount in the wrong location. My TCR has the same mount and it looks the same to me and mine works great and looks right also. Maybe the OP has a bent mount or perhaps the derailleur is just out of adjustment and it is sitting out too far, who knows for sure. Hard to diagnose if your not actually looking first hand at all the various factors that could cause the issue.

Here is mine, looks like it is in the same place.


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## wim (Feb 28, 2005)

davcruz said:


> I have a hard time believing that Giant put the mount in the wrong location.


I do too. Something got bent or is installed catawumpus. Take the cable off, take the derailleur off, then reinstall.


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## bikerjulio (Jan 19, 2010)

this thread is sure showing a lot of horrible FD setups. 


would it be so hard to measure?


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## goodboyr (Apr 19, 2006)

Lol. So much gap on that last one.


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## Camilo (Jun 23, 2007)

wim said:


> I do too. Something got bent or is installed catawumpus. Take the cable off, take the derailleur off, then reinstall.


This is what should be done - remove and start over. Inspect carefully to make sure neither the "braze on" or the derailleur is bent (which would be my guess)

Can Davcruz's picture be reduced - it's really messing up this thread on my browser.


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## davcruz (Oct 9, 2007)

Camilo said:


> This is what should be done - remove and start over. Inspect carefully to make sure neither the "braze on" or the derailleur is bent (which would be my guess)
> 
> Can Davcruz's picture be reduced - it's really messing up this thread on my browser.


I deleted the picture, I swiped it from the web and did not realize it was that large, apologies.


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## davcruz (Oct 9, 2007)

goodboyr said:


> Lol. So much gap on that last one.


LOL, it is 3 mm at the front which is Shimano spec, the angle I took the picture at is weird, that's all.


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## Kerry Irons (Feb 25, 2002)

wim said:


> Could be the wrong hanger or a bent one.


I'm definitely going with a bent hanger. Notice how the back of the cage is SO much closer to the chain ring than the front of the cage. Typically it is the other way around (back a little farther from the ring than the front). I think the hanger (or the derailleur body) is bent so that the cage doesn't follow the curvature of the chain ring.


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## headloss (Mar 3, 2013)

davcruz said:


> I deleted the picture, I swiped it from the web and did not realize it was that large, apologies.


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## looigi (Nov 24, 2010)

davcruz said:


> LOL, it is 3 mm at the front which is Shimano spec, the angle I took the picture at is weird, that's all.


LOL. 3mm spec is for FD is small ring, not big ring as pictured. (or with the outer plate of the cage directly over the big ring)


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## headloss (Mar 3, 2013)

looigi said:


> LOL. 3mm spec is for FD is small ring, not big ring as pictured. (or with the outer plate of the cage directly over the big ring)


The tech doc says 1-3mm, so it is "in spec." I wouldn't run that much of a gap myself.


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## davcruz (Oct 9, 2007)

looigi said:


> LOL. 3mm spec is for FD is small ring, not big ring as pictured. (or with the outer plate of the cage directly over the big ring)


The 3 mm that I noted is 3 mm as measured when the FD is in the lowest position and it is measured to the outer ring if I am not mistaken. You do not setup a FD in the outer position unless you have the forearm strength of a bear. It is placed while in the loose cable position. Now, I did not setup the derailleur as it is now, a mechanic at the shop did it when I was in there for a cable and he decided to be nice and install the new cable for no charge and he moved the derailleur a bit at the same time. I am fairly sure it is in spec and it shifts perfectly and it has nothing to do with the OP's concern. I merely posted the pic to show the location and type of derailleur hanger.


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## wabasso (May 18, 2012)

bikerjulio said:


> Looks like a home made tab, either screwed or pop riveted to the front of the seat tube.
> 
> Notice the absence of a slot.
> 
> ...


It is screwed on, if you look closely you can see the screw head just below where the mounting slot should be.


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## bikerjulio (Jan 19, 2010)

wabasso said:


> It is screwed on, if you look closely you can see the screw head just below where the mounting slot should be.


Yes, I was corrected and we are past that. Some think it's bent. I had looked up the Shimano frame spec. for tab placement and was hoping that someone would measure their Giant, since it still looked off to my eye, but perhaps it's just the camera angle.

Regardless of the cause, it would still seem to me, an easy thing to remove the standard tab and replace with a clamp that would provide more adjustability.


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## davcruz (Oct 9, 2007)

What do want a measurement of BJ? 

Also, I took a minute to check the placement of my FD since all of the constructive criticism I received after I posted my picture and it measured 4 mm when in the most outer part of the range so I reset the derailleur and now it measures closer to 2 mm in the same position.


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## bikerjulio (Jan 19, 2010)

davcruz said:


> What do want a measurement of BJ?
> 
> Also, I took a minute to check the placement of my FD since all of the constructive criticism I received after I posted my picture and it measured 4 mm when in the most outer part of the range so I reset the derailleur and now it measures closer to 2 mm in the same position.


I'm agreeing that it's not too likely that Giant got it wrong, although one of the pictures makes it look a little too far forward, which would cause the problem. But then so would a bent tab.

From the link to Shimano frame dimensions I posted earlier is this drawing which shows the correct location.


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