front derailleur + idiot (me) = confused

6 replies [Last post]

Sun, 03/11/2007 - 4:43pm

Anonymous

"I've got a Shimano Ultegra front derailleur & a compact 50/34 chainring, and whenever I'm in the big ring/small cog combination the outside of the chain is rubbing against the inside of the front derailleur cage.

I've been hesitant to do any tweaking myself, as A) I have no wrenching experience beyond washing & lubing; and B) Lennard Zinn's book is a bit oblique about addressing this specific topic. But then yesterday's mail brings me ""Bicycling Magazine's Bike Tune-Up Guide"", and right there on page 15 is what seems like a clear, concise explanation of how to fix my particular problem:

""Shift into the largest cog and smallest chainring combination. Look between the inside of the front derailleur cage and the chain. There should be 2mm of space. If not, turn the inner limit screw (usually the closest to the frame) until you get that 2mm of clearance. Next, shift to the smallest cog, biggest chainring combination. The outside of the cage should clear the chain by 2mm. Adjust the outer limit screw, if needed.""

Ahem. Yeah, so, well, I try this and...nothing. Cage doesn't move at all. I try tighter, I try looser, nothing, nada, zip, zilch. I figger maybe I'm turning the wrong screw, so I try the inner limit screw. Nope. (Plus -- separate problem, I guess -- now I can't get the inner limit screw back in!)

Help! Any ideas what I need to do to get the front derailleur cage to not rub against the outside of the chain when I'm in the big chainring/small cog combination?

Thanks."

Mon, 03/12/2007 - 1:24pm

JIM N (not verified)

Cable tension or position of the derailer

I'd guess that in order to get the front derailer (Sheldon Brown spelling) to move over that extra little bit, you'd have to let out some cable. An easy way to move it just a tiny bit is to put a vise-grip on the cable where a couple of mm from where it comes out of the derailer's clamp bolt. Then loosen the nut, let the tension out, and tighten it back up. You will probably have to re-adjust your H/L screws.

BUT before you do that, check that the derailer itself isn't bent or, if it's a clamp-on, skewed slightly on the seat tube.

Sun, 03/11/2007 - 5:11pm

David Schlichting (not verified)

From your description, it sounds as though the limit screw that controls the outer most movement of the FD was already fully retracted, so to speak --which explains the lack of action and the fact that it is now removed.
And to remove 3 potential variables, you may also look at the inside of the FD and make sure that there is no dirt or whatever in between the limit screws and their contact points. Make sure the cable does not have excessive play it in, otherwise, your shifter will run out of cable before you FD runs out of movement. Finally, make sure your right crank arm is on tight.

Sun, 03/11/2007 - 5:27pm

Morene (not verified)

large chain ring/small cog

Hey, Bob. It's funny you posted this, as I was riding behind you observing same for a number of miles today!~ I don't have a compact, but was told NOT to use the large front/smallest cog combo. I don't know if it's much different for compact chain rings, but I thought I'd pass it on to you. Mine grinds slightly even in the large front/third-smallest cog, which I'm sure is just an adjustment, but I HATE the sound so I just switch to the large chain ring.
Anyway, you're a very strong rider (especially uphill) and I'd take your draft any time!
Morene

Mon, 03/12/2007 - 12:17pm

DvB (not verified)

"No offense to the person who told you not to use the large-front/small-rear combo, but, in the same way Rick went to Casablanca for the waters, your friend was misinformed. The small-front/small-rear combo should be avoided, as should the large-front/large-rear combo. Otherwise, every other combo should be available.

If you're experiencing rubbing on either inside surface of the front derailleur sideplates, you SHOULD be able to quiet the rub with a slight tweak of the shifter itself. Much easier on Campy, given that Shimano sort of ""indexes"" its front shifters. If a shifter tweak doesn't work, it's likely one or more of the following four issues: (1) incorrect height of the derailleur vs. the chainrings; (2) incorrect angle of the derailleur vs. the chainrings; (3) incorrect stop-screw settings; or (4) incorrect cable tension. The good news is they're all very easy fixes. Five minutes with a good mechanic and you'll be back in bidness.

--DvB"

Mon, 03/12/2007 - 1:00pm

Paul (not verified)

I'll take your bet and up it

I keep it simple and simply say that all extremes should be avoided as it decreases efficiency as well as puts added stress on the chain (and the sprockets in certain scenarios) so one should avoid both a 53X23 and a 40X13. If you can't remember this then keep an open ear when riding as these extreme conditions will create an pretty unique sound (in addition to the sound of money leaving your wallet).

Besides, it makes good sense going to a 53X17 (82 inches) when you want to up shift from a 40X14 (76 inches).

Mon, 03/12/2007 - 1:59pm

Evan Marks (not verified)

pliers

Sometimes the only thing left to do is open up that front derailer a bit. Would I do that to my own bike, you ask? Sure. Already have.

How did mankind survive before vice-grips and duct tape?

NYCC.org

front derailleur + idiot (me) = confused