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Problem with braze-on front mech. Frame faulty?

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Problem with braze-on front mech. Frame faulty?

Old 04-02-20, 12:46 PM
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touring_bmore
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Problem with braze-on front mech. Frame faulty?

SOLVED: I was missing the curved radius washer that goes between the bolt and the derailleur mount on the frame. Thank you for the help!

Hey everyone,

I just finished building up a Bowman Palace:R frameset with a new Ultegra R8000 Di2 groupset. But when I install the front mech, the lower end of the cage seems to be angled outwards and the upper end inwards. It's so bad that the chain rubs both at the top and the bottom. Even the teeth of the chainring touch the cage and catch it no matter how high I move it.

I can just not get the cage parallel to the chain. And the way I understand the manual, with the support bolt, I can angle the cage further outwards but not inwards. This is not the first time I am building up a bike, but the first time with Di2, so I carefully followed all the steps from the Shimano manual. Right now, the support bolt is not touching the frame so it's not responsible for it. I am also pretty certain that the cage of my brand new derailleur is not bent out of shape:

Normally, I would just rotate the derailleur clamp to align the cage but the Bowman Palace:R is only compatible with braze-on derailleurs. The only explanation I can come up with is that the braze-on bracket on the frame is mis-aligned.

Am I making a mistake or is there anything else I can try? Or do I have to send the frame back to Bowman Cycles and ask for a refund?



Thank you for your help!






front mech cage angled outwards

big chainring touches front mech cage

Last edited by touring_bmore; 04-03-20 at 11:18 PM. Reason: problem is solved
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Old 04-02-20, 12:52 PM
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CliffordK
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Have you tried loosening the bolt and rotating the derailleur? You may have to get it fairly loose, and make sure the bolt actually shifts as you twist. Most derailleur braze-ons have a fair amount of up down, and twisting adjustment, although I've seen some OEM setups that are designed for a single derailleur with less adjustability.
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Old 04-02-20, 01:08 PM
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Iride01
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I think there is an adjustment bolt on on the portion you clamp to the braze on that controls that angle. Don't know if it's a give and take between two screws, or just one screw does it all. I've not taken them off or put them on myself. But I have one and it looks like kinda, sorta, maybe that it what I'm seeing.

Have you read the DM on Shimano's tech doc site?
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Old 04-02-20, 01:24 PM
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So it looks like the derailleur cage is tailed out, and you can't align the outer plate parallel with the chainrings. Is that correct? Just trying to get a handle on this.

Never mind, I read more closely and I get it. It sounds like the mounting tab has a twist to it that's causing the cage to tail out when it's at the correct height. This is a defect. There are two ways you can deal with it. One, contact the warranty department for instructions on getting a replacement frame. Two, if the this is an alloy frame remove the derailleur and try to straighten it with an adjustable crescent wrench. I'd try one first. The tab is supposed align 90 degrees from the frame centerline, be more or less parallel with the seat tube, and have a slight curve that is uniformly straight top to bottom.

We had a similar problem wit a customer's Project 1 Madone a few years back. The tab was angled forward so we could not align the cage parallel to the chainrings. It angled out a little, despite our best efforts. It was carbon fiber and was not going to be bent. We should have warrantied the frame, but due to other screw ups management made an executive decision and it still shifted as well as any of his buddies' bikes. But I was relieved when he crashed it and we got him on a crash replacement, a race stock Domane.

Last edited by oldbobcat; 04-02-20 at 01:48 PM.
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Old 04-02-20, 01:48 PM
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It sounds like you know what you are doing as this is not the first bike that you have built. Your pictures and explanation lead me to agree with you that the braze-on clamp is misaligned. In that case it is a manufacturer defect....and that can happen.
Good luck.
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Old 04-02-20, 06:18 PM
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woodcraft
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A bit of filing on the braze-on bracket slot or the curved FD washer may get the range that you need.

Look carefully at what is preventing it from rotating enough.
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Old 04-02-20, 08:15 PM
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CliffordK
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It isn't bumping on something like the wire is it?
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Old 04-02-20, 08:18 PM
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This may help.

Last edited by Crankycrank; 04-02-20 at 08:21 PM.
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Old 04-02-20, 08:25 PM
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Originally Posted by CliffordK View Post
Have you tried loosening the bolt and rotating the derailleur? You may have to get it fairly loose, and make sure the bolt actually shifts as you twist. Most derailleur braze-ons have a fair amount of up down, and twisting adjustment, although I've seen some OEM setups that are designed for a single derailleur with less adjustability.
Thank you, yes I have tried that. I can move the derailleur up and down no problem. But there is no way to twist it. The mount fits the curvature of the front mech like a glove and when I tighten it just enough to secure it, it gets forced into this outward angle.

Originally Posted by Iride01 View Post
I think there is an adjustment bolt on on the portion you clamp to the braze on that controls that angle. Don't know if it's a give and take between two screws, or just one screw does it all. I've not taken them off or put them on myself. But I have one and it looks like kinda, sorta, maybe that it what I'm seeing.

Have you read the DM on Shimano's tech doc site?
Thank you, I have read the DM by Shimano. There is only 2 adjustment screws. The top adjustment bolt moves the cage parralel inwards or outwards but does not change the angle. And the support bolt can push against the seat-tube and angle the cage further outwards. But it's already too far outwards. So if I screw this bolt further in, I'm only making the problem worse.
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Old 04-02-20, 08:36 PM
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Originally Posted by woodcraft View Post
A bit of filing on the braze-on bracket slot or the curved FD washer may get the range that you need.
Look carefully at what is preventing it from rotating enough.
Hmm... I don't really want to start filing on the bracket when it turns out to be a warranty case. And when I make the slot in the bracket wider, not only will the front derailleur be less secure in place, by twisting it inside the curvature of the mount, I will also loose this flush fit that it currently has and it will become very fiddly to adjust.

Originally Posted by CliffordK View Post
It isn't bumping on something like the wire is it?
No I wish it was though...

Originally Posted by Crankycrank View Post
Thank you, great video. But doesn't solve my problem. I can only move the cage horizontally or change the angle with the set screw so that it kicks further outwards. But there is no way to adjust the angle to make the end move inwards.
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Old 04-02-20, 08:45 PM
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Originally Posted by oldbobcat View Post
So it looks like the derailleur cage is tailed out, and you can't align the outer plate parallel with the chainrings. Is that correct? Just trying to get a handle on this.

Never mind, I read more closely and I get it. It sounds like the mounting tab has a twist to it that's causing the cage to tail out when it's at the correct height. This is a defect. There are two ways you can deal with it. One, contact the warranty department for instructions on getting a replacement frame. Two, if the this is an alloy frame remove the derailleur and try to straighten it with an adjustable crescent wrench. I'd try one first. The tab is supposed align 90 degrees from the frame centerline, be more or less parallel with the seat tube, and have a slight curve that is uniformly straight top to bottom.
Thank you, this is exactly what I think. It just makes my heart bleed a little to take everything apart again and send the frame to UK for a replacement
I'm thinking of sourcing another braze-on front mech and try to fit it. Just to make sure, the new Di2 derailleur is not out of alignment for some weird reason. Then I'll probably have to contact the manufacturer about sending it in to replace it.
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Old 04-02-20, 10:06 PM
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woodcraft
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You do realize that the curved braze-on, curved surface of the FD the mates with it, and the wider-than-the-bolt slot

are designed to allow the FD to rotate for adjustment? Most do not have that little adjusting screw.
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Old 04-02-20, 11:15 PM
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CliffordK
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You might try a shim. Perhaps try cutting a piece of soda/beer can and slip it between the bracket and the derailleur, just filling the outside half of the bracket, and nothing on the inside half. A bit crude, but if it works, you could epoxy it into place.
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Old 04-03-20, 01:26 AM
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tFUnK
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Do you have another FD to try? Without pics of the braze on tab it's hard to pinpoint the issue. Is the braze on tab bendable?
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Old 04-03-20, 07:26 AM
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Have the frame maker do it correctly. Mis-aligned front derailleur braze-on tabs are not unprecedented.

In the late '90's I ordered a Co-Motion S&S coupled single bike frame and specified NO fd braze-on tab as I had a braze-on fd but intended to use it with an adapter clamp. Not only did Co-Motion braze on the tab but misaligned it so I couldn't even fit the fd I had. At least they paid shipping both ways to solve the problem.
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Old 04-03-20, 10:41 AM
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It's times like this that I use an open end adjustable wrench (Cresent wrench) and a pair of pliers to do the final adjustment (Bend the cage).
I actually like the Front DR kicked out just a bit. Tweak where it rubs.
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Old 04-03-20, 12:12 PM
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Originally Posted by touring_bmore View Post
Thank you, yes I have tried that. I can move the derailleur up and down no problem. But there is no way to twist it. The mount fits the curvature of the front mech like a glove and when I tighten it just enough to secure it, it gets forced into this outward angle.

.
I had similar but not as bad problem.....I had to get help to hold the position when tightening........
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Old 04-03-20, 02:13 PM
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Originally Posted by touring_bmore View Post
Thank you, this is exactly what I think. It just makes my heart bleed a little to take everything apart again and send the frame to UK for a replacement
I'm thinking of sourcing another braze-on front mech and try to fit it. Just to make sure, the new Di2 derailleur is not out of alignment for some weird reason. Then I'll probably have to contact the manufacturer about sending it in to replace it.
I've never seen a Di2 front derailleur that hasn't been in a crash tweaked like that. Since the bike is alloy and the tab is thin and the misalignment is small in the overall scale of things, you might be able to bend it with an appropriately sized adjustable wrench. A disk brake rotor straightener might work, too. Just remember if you have to use a cheater bar or something stiffer than a workstand to hold the bike, or if your efforts look like they're putting stress on the seat tube itself, you might break something. If you think what you're doing might break it, do something else.
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Old 04-03-20, 03:30 PM
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Originally Posted by Crankycrank View Post
Be aware that this video is over 7 years old and shows adjustment for the 2 generations old FD-6770. While some of it is still applicable, the adjustment steps referenced are not correct for the current gen. FD-8050. Once the cage is aligned (problem OP is having), the large ring adjustment (mechanical screw) is made, then the small ring adjustment (electrical using shift levers while in adj. mode) and finally the large ring adjustment (electrical using shift lever while in adj. mode). There is no small ring mechanical adjustment (limit) screw on the FD-8050. Probably better just to use the Shimano instructions which are laid out step by step and pretty easy to follow IMHO.

Shimano Di2 Dealer Manual

Shimano Manuals & Technical Documents
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Old 04-03-20, 11:17 PM
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Thank you all for the suggestions!!
My mistake was not using the curved washer between the mounting bolt and the derailleur mount.
It wasn't included with my derailleur and in the Dealer manual it looks like a normal flat washer. I picked up a curved washer from my bike shop and then could adjust the angle to make it work. It's still not absolutely perfect but close and shifting now works great.
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