Campy front derailleur limit screw-up

[daker13]

I'm installing a Centaur braze-on front derailleur on a bike that otherwise has a silver Chorus 10 speed build and I can't get the low gear limit screw to back off the cage for the required .5 mm... Thought I had it at one point, but now I'm having a devil of a time. Any tips would be helpful, it's been a few years since I last did this.

[Black Dog]

I'm installing a Centaur braze-on front derailleur on a bike that otherwise has a silver Chorus 10 speed build and I can't get the low gear limit screw to back off the cage for the required .5 mm... Thought I had it at one point, but now I'm having a devil of a time. Any tips would be helpful, it's been a few years since I last did this.

Is the cage parallel to the chain rings? You can rotate it inward to get the gap.

[daker13]

Is the cage parallel to the chain rings? You can rotate it inward to get the gap.

It is, I think it won't be parallel if I move it inward but I'll give it a try... Seemed like the limit screw was not moving the cage perceptibly, is that possible?

[Ralph]

Is the cable too tight.....effectively acting as a stop.

[oldpotatoe]

It is, I think it won't be parallel if I move it inward but I'll give it a try... Seemed like the limit screw was not moving the cage perceptibly, is that possible?

Could be the front der is as far inboard as it will go.

[daker13]

Is the cable too tight.....effectively acting as a stop.

This is with the cable unattached.

I have the shifting reasonably good now, only rubbing a bit in the extreme combinations. Thanks all!

[oliver1850]

I've built lots of bikes with C9/C10, never had that problem. What models of crank, BB, FD, shifter, and frame?

[daker13]

I've built lots of bikes with C9/C10, never had that problem. What models of crank, BB, FD, shifter, and frame?

Beyond what I said above? The frame is an MX Leader.

The basic problem is that the low limit screw isn't going inwards enough to clear the chain when it's in the biggest sprocket, and in fact I'm getting very little movement from the low limit screw at all... could the spring on that screw lose its tension? Otherwise the shifting is ok. Could also be that the cage itself is bent, I suppose.

[oliver1850]

Yes, specific parts might give a clue, there are lots of Centaur FD models. My MXL is Chorus 9 with a Daytona FD. I can turn the limit screw out a full turn from where it's properly adjusted before the cage stops moving. The big cog on the cassette is farther inboard on a 10 speed setup, so that could be the difference. You might try taking the FD apart and removing a bit of material from the area on the links where they touch with the screw all the way out. That will provide more inboard travel. You will have to rotate the inner link away from the cage and have a helper stick something (pencil) in the gap to keep the links separated so you can file the necessary spot. You might also gain enough by rotating the FD on the mount slightly.

[zmudshark]

Is this a compact/triple set up?

[Mark McM]

Yes, specific parts might give a clue, there are lots of Centaur FD models. My MXL is Chorus 9 with a Daytona FD. I can turn the limit screw out a full turn from where it's properly adjusted before the cage stops moving. The big cog on the cassette is farther inboard on a 10 speed setup, so that could be the difference. You might try taking the FD apart and removing a bit of material from the area on the links where they touch with the screw all the way out. That will provide more inboard travel. You will have to rotate the inner link away from the cage and have a helper stick something (pencil) in the gap to keep the links separated so you can file the necessary spot. You might also gain enough by rotating the FD on the mount slightly.

Maybe its an optical illusion, but in the photo it looks like the seat tube is oversized, and ovalized at the BB (tube is laterally wider). If so, this could push the derailleur tab a few millimeters outboard, so that the derailleur can not retract as far inboard as one might like. If this is the case, than the solution for chain derailleur clearance would be to offset the cranks/BB to the right a millimeter or two. This should be easy to do with a threaded BB, where you can place a BB spacer under the lip of the driveside cup.

[oliver1850]

Maybe its an optical illusion, but in the photo it looks like the seat tube is oversized, and ovalized at the BB (tube is laterally wider). If so, this could push the derailleur tab a few millimeters outboard, so that the derailleur can not retract as far inboard as one might like. If this is the case, than the solution for chain derailleur clearance would be to offset the cranks/BB to the right a millimeter or two. This should be easy to do with a threaded BB, where you can place a BB spacer under the lip of the driveside cup.

That's certainly an option if he's using a ST BB. I don't think it would take more than a 1 mm shim to gain enough clearance.

[oldpotatoe]

Beyond what I said above? The frame is an MX Leader.

The basic problem is that the low limit screw isn't going inwards enough to clear the chain when it's in the biggest sprocket, and in fact I'm getting very little movement from the low limit screw at all... could the spring on that screw lose its tension? Otherwise the shifting is ok. Could also be that the cage itself is bent, I suppose.

Have the same issue on my MXLeader pre EPS. Ovalized seatube puts front der pretty far outboard in relation to crank. A little tail in moving or ‘bending’ to clear the chain when in lowest gear.