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TL;DR: if you have a SRAM Rival front derailleur I'd love to know if yours looks "funny" like mine does--it's described in bold.

I have a SRAM Rival groupset (from late 2011), including front derailleur/mech, crankset, and brifters. It all works fine except the front derailleur, which is a nightmare.

The bike is just under two years old. For the first six or eight months (but that included five months of winter), everything was fine. But one day I shifted from the small to the big ring, and it threw the chain right off the outside. It worked sort of OK much of the time for a few months, but maybe one shift out of ten, it would throw the chain (always to the outside). It started to get worse, and I tried adjusting the cable tension and limit screws, all to no avail. If I adjusted a bit farther down, it would never shift to the small ring. Up a bit and it threw off.

I took it to a quite professional cycle shop, and for about $20 they adjusted it. From what I could tell and what they told me, they reoriented the derailleur on the seat tube, moving its rear slightly outward (not sure about height adjustment). It worked fine for a few rides. Then it went back to the way it had been, throwing the chain off.

I kept trying to adjust it myself, but it would either not shift up, or it would throw the chain outside. Or it would sometimes shift properly, but only if the rear was around gear 6 (of 10), and not otherwise.

Now I have read the SRAM manual, watched videos online, followed all the steps from initial installation (including completely removing the clamp, cleaning, and reinstalling). I moved the derailleur down as far as I could without overlapping the big ring teeth. I carefully adjusted everything. And I'm right back where I started: either it won't shift up, or it throws straight off.

There are two things that look strange. First is that the outer plate of the derailleur is not what I would call straight. Rather, it seems to veer inward (toward the bike's centerline) at the back of the cage. That is, the outer plate and inner plate do not appear to be really parallel--but I don't think it was ever any different.

The second weird thing is how the chain throws off the outside. It's like the shift is mostly going OK, but only about one link of chain sits where it should, and then the tendency of the chain to go straight when viewed from the top causes it to just run at the same angle from the small ring to the big one and right onto the crank arm. It's sort of hard to describe this, but when I watch closely while shifting, it's hard to see how it's ever going to work well.

For a number of reasons I wonder if the derailleur is actually broken. But it looks fine, and the shop I took it to last time (which sadly is now across the world from me, or I'd go back) said it was OK. And there was no crash or anything else to cause it in the first place.

I've been fixing my own bikes for two decades. This one has me stuck (and I'm not looking forward to visiting another shop with it, partly because the shops where I live now mostly don't seem that great). Do you think the derailleur is simply broken and needs replacement? How would I even tell?

Finally, some people apparently use Shimano 6800/7800 front derailleurs with SRAM shifters. Some of them claim it works much better. Any thoughts on that? Parts are expensive where I live, so I'm a little hesitant to go buy an Ultegra or Dura-Ace part unless I'm pretty sure it will work.

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2  
Pictures please –  joelmdev Sep 10 '13 at 13:03
    
Is it possible there is a twisted link in your chain??? –  WTHarper Sep 10 '13 at 13:40
    
@jm2: I haven't figured out how a picture would help much. The derailleur basically looks the same as the pictures you can find online. Taking a close-up shot will likely have so much distortion that it won't be illustrative. That's why I tried to describe it: the tail end appears narrower than the front, though it's hard to see how it could be "bent," it looks like it was made that way from the beginning. Still, if you or others really want pictures I can try...it's just a very tight spot as it's mounted on the bike. –  John Zwinck Sep 10 '13 at 14:05
    
@WTHarper: I don't think so? The same symptoms happen all the way around as I pedal--it's not like it sometimes doesn't shift at certain points along the chain. It's quite consistent actually. And the chain (matching SRAM model) had no more than 500 miles on it when this started happening. –  John Zwinck Sep 10 '13 at 14:06
    
Another way to look at it is that the outer plate (the continuous part, not counting the "lip" near the front bottom which is tucked inward) is not straight. Should it be? That is, on my derailleur, if I put a ruler up against the outer plate, it does not sit flat across the entire length, but rather seems to show one flat area in the front 40% and then a slight (like 3 degree) bend and then the rear 60% is straight but relatively speaking at an angle where the tail points inward toward the bike centerline. Is that normal for this sort of derailleur? –  John Zwinck Sep 10 '13 at 14:10

3 Answers 3

A few things to check:

  • Check the derailleur height to the outer chain ring. Basically, this should be as close as possible without hitting the chainring. Make sure it's well secured to the frame.
  • When you adjust the travel, put the bike into the large chainring, small cog and make sure there's no more than about a 1mm of distance between the outer edge of the chain and outside plate of the derailleur.
  • Make sure you don't have a bent a tooth on your chain ring.

The only time I've had a chain go over the top of the outer chain ring is when the limit isn't properly set or the outer cage isn't more or less parallel to the chain ring. Remember, to get the derailleur over and outside of the chainring, there has to be enough clearance for the chain to make it.

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As Rich mentioned by first action would be to check the derailleur height...

I kept trying to adjust it myself, but it would either not shift up, or it would throw the chain outside. Or it would sometimes shift properly, but only if the rear was around gear 6 (of 10), and not otherwise.

To me, it sounds like the derailleur sits too heigh, or the adjustment of the L-screw has gone wrong.

Try adjusting it yourself once you checked the height of the derailleur... Not all "pro's" are equally good at gear adjustments: http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

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up vote 1 down vote accepted

Well, I took it to a local bike shop, and they fixed it, seemingly. I will see how it goes in a few months, but for now it works fairly well.

In trying to fix it myself I had moved the derailleur down a bit, so it was exactly 1mm above the big ring. The shop guy moved it back up, and also moved the tail out slightly I think. He also loosened the cable--I didn't think this would make much difference, but according to him the cable was previously too tight and this encouraged the overshooting. And of course he adjusted the high limit screw (that's what he started with too, but that alone was insufficient).

So, notes for next time: moving the cage lower didn't help, loosening cable tension slightly may have, and I think making the tail point slightly outward (away from bike centerline) seems viable. Oh, and I think you need a shaman to get these SRAM FDs working perfectly--next time consider a Shimano Ultegra mech instead, because in two decades with four Shimano bikes I've never seen anything so hard to adjust properly.

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I don't think its SRAM's fault that the thing wasn't setup properly - tons of people have been running rival without problems. Also, iirc, SRAM Rival is closer to 105. –  Batman Mar 11 at 6:30
    
Well, after taking it to the new LBS as described in this answer, three months later it was throwing the chain off again. We're talking less than 1000 km of riding here, and not very many front shifts at all. After a half-dozen phone calls I got SRAM to agree to authorize the LBS to replace the FD under warranty. Still waiting for the part to arrive. I hope it works better than the last one. –  John Zwinck Mar 12 at 12:17

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