Sram Etap front derailleur problem
 

I have had etap for a couple of months and have been having a problem with the fd. I have a full sram red set up. All worked well when first fitted by lbs. Then after about three weeks and a couple of hundred miles the chain started to come off when changing to the big chain ring. Not everytime. About three times in a ten mile ride.
Lbs checked fd set up and set the limit screw a bit closer. This seemed better but the same problem recurred. Took it back and they sent fd back to sram. Sram said nothing wrong with fd so it was refitted and set up again.
Worked for a couple of weeks then today chain shipped at least 12 times in 25 miles.
I checked the limit screw and the gap was to my eye about 2mm instead of.5 So I turned the screw half a turn. Tried it on the stand - worked fine. On the road it would not change so I turned the limit screw back a quarter.
It now changes fine but after a few changes it still came off!
After riding up and down the road for ten minutes changing up and down it came of twice.
I cannot work out what is wrong. When it changes correctly it is so smooth. Under pressure, free wheeling, up hill, on the flat, down hill makes no difference. Then it seems to clatter and of it goes onto the crank for no reason.
Any ideas?

Locktite on the limt screw

What chainrings do you have on your crankset?

Sram red

You might find something useful in this thread: Etap problems - Weight Weenies

I would definitely check chainring alignment and crank arm movement.

Is it a mid-compact?

One is tempted to chalk it up to the grand tradition of SRAM road front derailleurs. (Mine functions perfectly, though. It's a Force 1x.)

I was going to joke that this response was either acceptance by SRAM that their FD sucks or a subtle hint to go 1X :p

34-50

Thee was a poster who couldn't get consistent FD shift. Turned out crankset did not have correct preload at the BB so it could move laterally. I think he needed a 1 mm spacer or something. Also check the block to prevent the FD from reacting to the torque load when shifting.

scott s.
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When in the small cog on the cassette and the small chain ring the chain catches on the pins on the back of the big chain ring. Is this significant?

Sorry, what do you mean by the "block"?

I see they don't show those any more on the installation vid or manual. Originally there were a couple different wedge-shaped blocks that fit between the FD fixed portion and the seat tube. You could select one that fit best. AFAICT, the idea was to prevent any flexing of the mount when the FD shifted outboard. Maybe SRAM decided they weren't really needed, but ISTR someone finding that it helped improve shifting. The other problem is sometimes the limit screws are too long and hit the crank arm. SRAM was supplying replacement screws that I guess were shorter.

scott s.
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Yes I know what you mean. We call them wedges. I have the biggest one on my bike. The fd seems to be very solid if you try to move it. It's the random nature of this problem that winds me up. If it did it everytime then you would know when you had solved it. Instead the system all works for 100 miles or so and then bang off goes the chain. Then it works for the next 6 changes then off again. Why?

Hi, that could mean that your chainline is a bit offset (the cassette is a bit more outboard, or crankset a bit more inboard). That could affect the front shifting when going from small to large chainring in combination with some rear cassette positions. Compare it to another bike you have and see in what gear combo the chain appears perfectly straight. May have nothing to do with it, but most of my bikes don't have the chain touching the front large chainring when in small/small as you describe. Some of mine do, however, and I don't notice any shifting issue.

Just to clarify, you are saying that when shifting from small to large ring the chain falls off the outside of the big ring toward the pedal, not into the bottom bracket?

It is the slackest chain position with the chain at its highest operating angle. In my experience, if you want a bad front shift to the big ring, that's the way to get it. It's the one combination I go out of my way to avoid.

Yes onto the pedal crank

I usually shift onto the big chain ring from the middle of the cassette. I don't actually use the small small or big big gears

The chain appears straight in the middle of the casette