Chain rub

[Marty]

Hi All , new member . My front derailer was rubbing on large cog . By time I finished it was ten times worse. It wouldn’t stay on big ring when I let go the shifter. I tightened and lossen the cable took me ages then it worked . But I have no idea how 😢 also the limt screws any easy way to tell which is which.

[G_M]

Hi! Welcome.
Did you have a look at the repair guides here?

How to adjust front derailleur: https://www.bikeride.com/adjust-front-derailleur/

[Jesper]

(04-20-2020, 03:27 PM)Marty Wrote:  "also the limt screws any easy way to tell which is which."

Hi Marty,
Welcome!
If you move the derailleur to it's farthest inner (small ring) or outer (large ring) range of movement, the screw that will turn without effort is the limiter for the opposite direction of movement since the derailleur "stop" is not contacting that screw, or the screw with the resistance is the screw that limits the movement in the direction that you are at for that specific ring. You will readily see the derailleur cage move in or out with a turn or two. It is best to set the shifter to low ring which is where the spring will automatically move the cage to with or without the cable attached. In that position, I would loosen the cable clamp on the derailleur and pull out the cable slack before re-clamping (a very little bit of slack is okay). Adjust the "low" limiter screw to keep the cage from moving the chain too far inward and making it track off of the cog. Move the shifter to make the chain track onto the largest ring and adjust that "hi" limit screw to keep the cage from travelling too far outwards avoiding the chain from tracking off that ring. The derailleur should be set so that the low side of the cage is about an 1/8" above the largest ring when shifted to that position, if you can go to 1/16" without shifting issues it will usually provide a cleaner/quicker chain transfer (depends on quality of the derailleur and condition). Make sure the cage is in proper alignment front to rear over your ring as this will also affect chain rub. I tend to adjust it for the rear gear(s) I ride use the most, if using the top 3 speeds on the rear, I set the alignment for the middle sprocket of those three cogs; only using 2 align it between the them (essentially your splitting the difference for the range of movement). If you are still getting rub, the bottom bracket may be worn/loose, and/or not adjusted correctly (for older loose/caged bearings, not sealed cartridge type BBs). That's just me, it does not apply to everyone. You'll probably have to make fine adjustment to the limiters while riding under load due to frame flex, especially if you are cranking hard. What I've said here is primarily the way I set things up, but to each his own; I ride the highest speeds almost exclusively and rarely use the smaller chain ring(s) so I pretty much disregard those for my set up unless doing a climbing set-up. That's a different story. Some derailleurs actually have the "hi and lo" screws marked on it.

Take care,
Jesper