Campy EPS weird problem...

[audiojan]

Hoping the collective knowledge can help me out... my wife's tri bike is acting really strange. The rear derailleur all of a sudden "forgets" the top gear and after a while, the second from top plus is starts to fall out of position (as in not shifting crisply from gear to gear). If I reset the power unit (with the magnet that plugs into it), I can set everything up again and it will work perfect for a while (sometimes an hour, sometimes for multiple rides).

I'm at my wits end. ANY idea will be helpful at this point.

[Llanberis]

Aside from zero setting, it may be that the cassette fitting is loose; might be worth checking if it's tightened up to 40 Nm.

[kulcha]

A bent hanger, perhaps?

[WESTMOTORSPORTS]

That is a classic sign that the upper limit screw is set too tight. If the power unit senses any resistance from limit screw, it will act just as you describe. Firstly, make sure that the hanger is correctly aligned. If it is aligned and all other gears shift well, a simple readjustment of the upper limit screw might be all it needs. To set the upper limit screw, shift into largest sprocket, then screw limit screw until it to "just" touches, then back screw off half a turn. If this doesn't totally fix your problem, align derailleur hanger, back limit screw off, reset settings, and then adjust set screw as instructed. Remember, the limit screw "IS NOT" a limit screw that limits travel when in use....it is a failsafe that if the power unit fails or the derailleur hanger gets bent, the derailleur will not travel into the spokes.

[Butcher]

I've run into this but I notice it right away. The clear sign was that I could not drop a gear after going to high. It would, but it would take a few seconds. I never waiting to see what happens if I left it out of adjustment.

[audiojan]

That is a classic sign that the upper limit screw is set too tight. If the power unit senses any resistance from limit screw, it will act just as you describe. Firstly, make sure that the hanger is correctly aligned. If it is aligned and all other gears shift well, a simple readjustment of the upper limit screw might be all it needs. To set the upper limit screw, shift into largest sprocket, then screw limit screw until it to "just" touches, then back screw off half a turn. If this doesn't totally fix your problem, align derailleur hanger, back limit screw off, reset settings, and then adjust set screw as instructed. Remember, the limit screw "IS NOT" a limit screw that limits travel when in use....it is a failsafe that if the power unit fails or the derailleur hanger gets bent, the derailleur will not travel into the spokes.

I should've been clearer. It's not the largest cogs, but rather the smallest cogs, so not related to the limit screw.

[audiojan]

Hanger is perfectly straight (and I replaced it just in case, but issue is exactly the same). Cassette is torqued to 40Nm.

It really seems like it's some kind of issue with the power unit. It's almost as if it's "senile".

[Mockenrue]

Have you done a zero reset?

[audiojan]

Have you done a zero reset?

Absolutely. First thing I did. Second was a complete reset with the magnet (plug in, not that strap).

I have no idea what caused this, but I took everything apart yesterday and reconnected it. Seems to be working. We're heading out for a ride this afternoon, so that will be the tell-tale sign