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105 Front mech support bolt woes

Old 01-19-21, 01:46 PM
  #1  
six four
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105 Front mech support bolt woes

Any help would be much appreciated. I cannot post a photo of this issue because I don't have enough posts under my belt which is a shame. It would be much easier to see what I was going on about.

The seat tube on my new build bike (De Rosa SK Pininfarina) is very thin where the braze-on front mech sits. The 105 R7000 unit I have installed has a support bolt that is supposed to rest against the seat tube (with a little metal sticker in place) or the braze-on bracket that comes attached to the frame.

The issue is that the bolt just makes contact with the very rear or the braze-on bracket. About half a mm or less is in contact. The rest of the bolt just rests against thin air because at that point the frame is only as thick as the width of the bracket (which is pretty small). It does not look at all secure!

One fix may be to upgrade the unit to Ultegra, if the bolt spacing is different. Does anyone know if the support bolt on the Ultregra unit sits just slightly further forward than the 105? In other words, towards to the front of the bike? Or, in other words the space between the support bolt and the bolt that fixed the unit to the bracket is less?

Alternatively, I may be able to fix a small nut or two to the bolt to give it more volume. So, more would rest against the bracket.

It's a long shot but I hope this makes some sense!!
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Old 01-19-21, 02:24 PM
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You might be on to something w/ the addition of a nut but photos would really help. Figure out some way to post a link or go take part in some threads.
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Old 01-19-21, 02:30 PM
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I would bet that all of the Shimano front derailleurs, that include that stabilizing bolt, have it in the same place. That bolt doesn't hold the derailleur on, it just resists the tendency for it to flex or move under shifting load. The bolt that goes through the front of the braze on mount is what secures the front derailleur. Front derailleurs have worked fine for many years before Shimano came up with the idea for that stabilizing bolt. Will it work better with the bolt in place? Sure. Will it work without it? Yes.
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Old 01-19-21, 02:38 PM
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Maybe build it out with the metal sticker?
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Old 01-19-21, 02:42 PM
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Originally Posted by cxwrench
You might be on to something w/ the addition of a nut but photos would really help. Figure out some way to post a link or go take part in some threads.
Yes, good advice, thank you. I will get my post count up and then post a picture. Thanks!
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Old 01-19-21, 02:46 PM
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Originally Posted by dsaul
I would bet that all of the Shimano front derailleurs, that include that stabilizing bolt, have it in the same place. That bolt doesn't hold the derailleur on, it just resists the tendency for it to flex or move under shifting load. The bolt that goes through the front of the braze on mount is what secures the front derailleur. Front derailleurs have worked fine for many years before Shimano came up with the idea for that stabilizing bolt. Will it work better with the bolt in place? Sure. Will it work without it? Yes.
Thanks for posting.

The 105 and Ultegra designs look almost identical from the images I have seen. I would be great to see both units in the flesh though just in case there is a small difference. I only need that bolt to be 2mm closer to the mount.

I understand the difference between the support bolt and the mount bolt but I am interested to hear that it will work without the support bolt. I thought that shifting could be unreliable without it?

Thanks!
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Old 01-19-21, 02:48 PM
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Originally Posted by shelbyfv
Maybe build it out with the metal sticker?
Thanks but the metal sticker has nothing to adhere too or the bolt would just flip it. I'll try to post a picture soon but you'll see that the pressure of the bolt would most likely lift the sticker - it is right on the edge of the bracket.
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Old 01-19-21, 07:44 PM
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Originally Posted by six four
Any help would be much appreciated. I cannot post a photo of this issue because I don't have enough posts under my belt which is a shame. It would be much easier to see what I was going on about.

The seat tube on my new build bike (De Rosa SK Pininfarina) is very thin where the braze-on front mech sits. The 105 R7000 unit I have installed has a support bolt that is supposed to rest against the seat tube (with a little metal sticker in place) or the braze-on bracket that comes attached to the frame.

The issue is that the bolt just makes contact with the very rear or the braze-on bracket. About half a mm or less is in contact. The rest of the bolt just rests against thin air because at that point the frame is only as thick as the width of the bracket (which is pretty small). It does not look at all secure!

One fix may be to upgrade the unit to Ultegra, if the bolt spacing is different. Does anyone know if the support bolt on the Ultregra unit sits just slightly further forward than the 105? In other words, towards to the front of the bike? Or, in other words the space between the support bolt and the bolt that fixed the unit to the bracket is less?

Alternatively, I may be able to fix a small nut or two to the bolt to give it more volume. So, more would rest against the bracket.

It's a long shot but I hope this makes some sense!!
Here’s a pic of the OP’s front derailleur.

$
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Old 01-19-21, 09:05 PM
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I installed my GRX FD without that stabilizing screw or plate - still shifts perfect 2 years later with no additional adjustments since initial setup.
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Old 01-19-21, 09:07 PM
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The screw is hitting the braze-on mount right? Don't worry about it, just set the derailleur up according to the manual and you're done.
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Old 01-20-21, 10:49 AM
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So the bolt is a couple mm too long? Then CUT IT dear six four CUT IT

A good strategy is to thread a nut on to the bold before cutting so after cutting you remove the nut and it helps clean up the threads.
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Old 01-20-21, 12:28 PM
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Originally Posted by ClydeClydeson
So the bolt is a couple mm too long? Then CUT IT dear six four CUT IT

A good strategy is to thread a nut on to the bold before cutting so after cutting you remove the nut and it helps clean up the threads.
No, bolt length is not his issue.
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Old 01-20-21, 12:45 PM
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Originally Posted by cxwrench
The screw is hitting the braze-on mount right? Don't worry about it, just set the derailleur up according to the manual and you're done.
I agree. all the bolt there for is as stopper to prevent twisting. the little foil piece is a paint protector and total pain to get in place (at least for me).
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Old 01-20-21, 02:40 PM
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Originally Posted by squirtdad
I agree. all the bolt there for is as stopper to prevent twisting. the little foil piece is a paint protector and total pain to get in place (at least for me).
It's actually a little stainless steel plate. When the derailleurs that came with them first came out a lot of the frames were apparently pretty thin in that area, now most have been reinforced and don't need the plate. When I was working for Trek they told us they definitely weren't needed anymore.
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Old 01-20-21, 03:43 PM
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Originally Posted by SalsaShark
I installed my GRX FD without that stabilizing screw or plate - still shifts perfect 2 years later with no additional adjustments since initial setup.
Sorry for the delay in responding but as a newbie I can only post five posts every 24 hours and I had reached my limit. I've had to wait the whole day before responding.

That's good to know and gives me another option if I cannot get the bolt to work correctly.
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Old 01-20-21, 03:45 PM
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Originally Posted by cxwrench
The screw is hitting the braze-on mount right? Don't worry about it, just set the derailleur up according to the manual and you're done.
Thanks for helping.
I'm fine with it hitting the braze-on mount. The issue is that it barely connects with the mount. Only a fraction connects (see pic) and I am worried it is going to slip. What I'd really like is a good connection with mount or the frame. But the screw isn't really hitting the mount and there is no visible frame in that area - it is all behind the mount.
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Old 01-20-21, 03:47 PM
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Originally Posted by shelbyfv
No, bolt length is not his issue.
Absolutely right. The bolt length is not the issue. The issue is that it barely connects with the mount and cannot connect with the frame because none is visible at this point (it is behind the mount).

Ideally, I would like to know whether an Ultegra front mech has the support screw in a slight different position. Just a couple of mm towards the mount bolt (towards the front of the bike) would sort this out. Or I can put a small nut on the bolt to give it more volume.
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Old 01-20-21, 03:50 PM
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Originally Posted by cxwrench
It's actually a little stainless steel plate. When the derailleurs that came with them first came out a lot of the frames were apparently pretty thin in that area, now most have been reinforced and don't need the plate. When I was working for Trek they told us they definitely weren't needed anymore.
I'm afraid this isn't the issue. I have no problem with the bolt hitting the braze-on mount but it barely connects (see photo). The frame is too slim (rather than the tube walls being too thin) in this area so it is completely hidden behind the braze-on mount. So there's nothing on which to mount a stick-on plate, even if I wanted too.

I hope this makes sense! :-)
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Old 01-20-21, 03:58 PM
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I seem to have caused some confusion with my original post. Sorry! And thanks for all the advice so far!

Essentially:

The seat tube in this area is very slim. Very slim. So the braze-on mount or bracket is the only thing facing the front mech. I'm not talking about the wall thickness but the diameter of the tube.

Therefore, the support bolt (which is just that, there for support to stop the mech twisting - there's a main mount bolt too) has to hit the braze-on mount or bracket. There's nowhere to place the stick on plate, because no frame is visible. Which I'm fine about.

The issue is that only about a quarter of the very thin bolt does connect. The rest of end of the bolt is in thin air. I'm worried that after a few changes it will just slip off the mounting bracket.

So, I'd love to know whether an Ultegra unit has a bolt mounted further forward that will make a better connection with the braze-on mount or bracket. It only needs to be 2mm further towards the front of the bike.

Does anyone have two units to compare?
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Old 01-20-21, 04:06 PM
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Originally Posted by six four
That's good to know and gives me another option if I cannot get the bolt to work correctly.
My install had the same problem as yours, where the screw was too far off to the side of the seat tube to do any good. Rather tham scratch up the paint on the tube with no added benefits, i simply left the stabilizer off the unit and binned the little adhesive metal plate.
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Old 01-20-21, 04:10 PM
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I think your best choices are to loctite a nut on the end of the screw or try to add something to enlarge the braze on. Either will give you more contact area. Or just try it w/o the screw. I have the similar 8000 but use a band adapter with the braze on FD. The screw rests on the band with plenty of purchase.
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Old 01-20-21, 07:36 PM
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Originally Posted by six four
I'm afraid this isn't the issue. I have no problem with the bolt hitting the braze-on mount but it barely connects (see photo). The frame is too slim (rather than the tube walls being too thin) in this area so it is completely hidden behind the braze-on mount. So there's nothing on which to mount a stick-on plate, even if I wanted too.

I hope this makes sense! :-)
I know...I was replying to someone else. Just adjust the screw against the braze-on mount and don't worry about it. It will work fine. I'm pretty sure those screws are located in the same place on the different models.
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Old 01-21-21, 05:10 AM
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I cbf using the plate on my own bike. On a customers bike it would be a different story but point being I don't believe you need the plate. May I suggest you ride the bike without the plate and then if you really think it's holding you back, install it later?
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Old 01-22-21, 08:46 AM
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Originally Posted by SalsaShark
My install had the same problem as yours, where the screw was too far off to the side of the seat tube to do any good. Rather tham scratch up the paint on the tube with no added benefits, i simply left the stabilizer off the unit and binned the little adhesive metal plate.
Thanks for the advice - it may come to that with mine too!
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Old 01-22-21, 08:49 AM
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Originally Posted by shelbyfv
I think your best choices are to loctite a nut on the end of the screw or try to add something to enlarge the braze on. Either will give you more contact area. Or just try it w/o the screw. I have the similar 8000 but use a band adapter with the braze on FD. The screw rests on the band with plenty of purchase.
Yes, I agree. My first line of action will be to fix a nut to the bolt/screw to give it more volume and a bigger, better contact area. I think this should probably do it.

If not, it is reassuring to know that people are running their front mechs quite successfully without the support bolt.

Thanks for your help!
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