Front derailleur woes...
I know there have been other threads on this, so I'm sorry. I couldn't find what I needed though.
I'm wrapping up frame #7 right now and the front derailleur looks like it's giving me some problems.
This first is the direct mount brazeon. I'm using the SRAM style one with a rival derailleur (it's a cross bike). How much room for error do I have? I have seen some of the documents on this, but I'm wondering how you go about positioning it. I've had some thoughts on a jig, anyone else do that?
Next is the fact that my derailleur is top pull and I have pretty much everything set for top tube cable routing. I was going to put a bottle boss in at the bottom of the seat tube and use that to put a pulley on. Has anyone else done that?
Thanks a bunch! any advice is always appreciated.
Wow, 7 frames, going strong.
Do you use cones on your jig for the BB?
You can add a plate to the center bolt and an arm out to the derailleur mount to hold it.
Position the pulley where it operates the derailleur best, a wrong positioning will not operate the pull arm fully through its swing. You will have to determine that for yourself. I presume you meant a bottom pull by the way.
If I don't make an attempt, how will I know if it will work?
You can also do what the old Yetis and Bontrager CX bikes had where you put a cable stop on the end of the derailleur arm and use it to 'push' the arm down.
Originally Posted by Eric Malcolm
That is sort of the what I was thinking for the jig, I just use a washer on the the drive side of my jig, so I was thinking about adding an arm on that to hold things in place. I'll just have to make sure I find out where that place is.
And I did mean a bottom pulley. It's good to know that it's position is important. i was thinking of just throwing something on there. Any tips on finding that sweet spot?
This sounds interesting. Would I have to braze it on? I'm not totally sure what you mean, but I do like the idea of full housing too.
Originally Posted by dr.welby
-You can miss by 2-3mm on the height and be ok.
-You can miss by several degrees on the angle (relative to the circumference of the seat tube) and be ok; the derailleur can be adjusted by something like 4-5 degrees either way
-If you miss by a little bit on the angle relative to the seat tube angle, you can cold-set a little bit without much difficulty; but if you use a pre-made brazeon and 28.6 seat tube it is hard to screw this up in the first place because it's premitered (to be more accurate, it's cast to fit the tube) so it'll tend to pull into alignment when you braze it on.
-Just put the pulley as low as you can. You are trying to imitate the cable routing of a true bottom pull (ie guide under the BB) so keep it low. If you get too high/close to the derailleur you can run into the problem Eric is talking about.
In short, don't get too intimidated - FD brazeons are designed/intended to be VERY forgiving of imperfect installation and allow a lot of adjustability for the derailleur to make up for any minor imperfections. Mock it up first and make sure it seems like everything will work, then go for it.
EDIT: I should make clear that I'm talking ONLY about road bike brazeon front derailleur mounting. Mountain bike direct mount derailleur setups are a totally different story and require more precision/are harder to deal with/allow much less adjustability to make up for improper mount positioning. I know respected professional builders who regularly freehand install road derailleur brazeons; nobody would try this for a mountain bike.
Originally Posted by adarn
Here's a pic, though I would braze a housing guide on the back of the seat tube instead of looping it around over the seatstay bridge (???). The end up the cable can be clamped under the bb.
Originally Posted by adarn
BTW, if you are doing a CX bike, you can get a top-pull XTR derailleur that will handle up to 48t. That's often a better option than a pulley if you're not planning to run a full-size road chainring.
Thanks a bunch, that's pretty much exactly what I was looking for. Thanks!
Looks like I'll just come up with a little jig to hold things in place and go for it. And same with the pulley.
In hindsight, I would have payed more attention to the components. I got this SRAM rival grouppo off a buddy for super cheap who won it in a race. I'm not too opposed to the pulley, it looks like a lot of people use them, just a little extra trouble.
A Sram xo or x9 mtb derailleur will work perfectly with your rival shifters. I'm planning on using some Sram Apex shifters on my next build for exactly the same reason as the OP.
Slowly slipping to retrogrouchyness
Cool. So I did it. It was no problem. Just to make sure I tacked it first though, checked and then finished, should work perfectly. I also put in a boss for the pulley and it looks like it's going to work just fine. I'll post pics when I get the frame back from powdercoat and built up. Thanks for the advice as always.