Nick Bain

So I finally have one of those WTF problems that doesn't make any sense.

In the smallest of gear combinations the chain is rubbing slightly on the FD so I loosened the cable and unscrewed the lower limit screw. Instead of the derailuer moving down it is hitting something and not making contact with the lower limit screw. After breaking my neck trying to see in their I find that the arm is hitting the side of the upper limit screw.

Chris_W

Any chance that you can take a photo? It is hard to visualize based on your description.

Nick Bain

so whats going on here is that the derailer bottoms out before hitting the set screw. What this means is when I shift to the big ring it goes further than it needs to becuase I cannot lower the L screw down far enough. When the derailuer is hitting the screw the chain is just almost touching the guide plate which is fine I guess but clearly this bike is at the limits of srams design.

Also there is a youtube video that says there is trim adjust for the small ring but on mine the trim adjust only works on the big ring.

https://www.youtube.com/watch?v=38vdA5OOBxI

rithem

sounds like a def Wtf moment, I've see some odd FD situations before. One mishap I had ended up being an issue with the cranks migrating a few mm's outboard with and italian thread square taper BB that wasn't tightened enough. I didn't see the forest thru the trees in that instance but figured it out. 1st clean that thing, reinstall align the FD properly double check cranks BB etc to be sure nothing is out of order. set the lower limit with the chain on the small ring/small cog about 1-1.5mm off the chain, reinstall cable set the outer limit. I know you are saying that the limit screw isn't doing what you think it should, but it doesn't make a whole lot of sense. Sometimes it's good to back to ground zero to eliminate variables you may not be aware of yet.

FBinNY 

Check your chainline. It's possible that your chainrings are too far inboard and beyond the range of the FDs inboard travel. If your chainline offset is low, and you have a spacer on the left side of the BB, switch it to the right and the problem should resolve.

Nick Bain

can that be done on a gxp BB? I have not taken one apart before.

FBinNY 

You won't be fooling with the BB, though I'm not sure of the specifics of yours. Typically the spindle is part of the right crank and slides through the BB with spacers used to locate it and fill the space to the arms. Look at the gap between the right and left cranks & the BB, and see if you have spacers there, and where they are. If there is one on the left, then you can remove the left crank, slide out the right crank and spindle and replace it with the spacer moved to the right side.

Before doing so, measure the chainring offset (distance from the center of the chainrings to the side of the down tube + 1/2 the diameter of the downtube). Then compare that to the data here.

dddd

In the picture, I can't see exactly what is hitting the side of the hi-limit screw, but agree with FB that this sounds a lot like a case of the crankset sitting a little too far inward.

I didn't catch whether this was a double or triple setup, but this problem seldom occurs with doubles in my experience.

Any chance that tuning the mounting angle of the derailer would assist with the inward clearance without having to exceed the derailer's swing limit?

Nick Bain

Basically its the arm of the derailuer hitting it, the same arm that the cable is attached to. I'll take it to the shop where I bought it because it has been like this since day one, I just finally got around to futsing with it. I don't trust myself with tourqing the BB or cranks anymore.

Not gonna angle it, I think the shop actually angled it, Is that wrong? If so it would be angled inward, which would be less sensible than the outward. I guess not with shrams new yaw angle feature. Which I believe angles out.


Also can some one tell me how the left brifter is supposed to work? as in the positions the shifter has. The video I posted is contradictory to how mine works as stated earlier in this thread. thanks.

Also I will check the chain line first but off hand I feel it should go in if anything. Stupid carbon bikes.