Yes the 7800 FD and 7900 compact crank don't work well together that is why I am looking to replace the FD. I think a 7900 FD and 7800 shifters will work? The new 9000 FD might be better and also work?

I am using a 7900 chain so that is not a issue.

The FD-7800 and 7950 cranks should not have any issues at all. Unless you were using 7900 shifters instead of 7800 shifters ?

No 7800 shifter but as a previous person mentioned the throw is a little short such that the gate rubs in 1st gear in the rear. I have also had many many issues with dropped chain and had the FD adjusted to many times.

7800 did not have a compact crank and I think that is the issue. My thought was to replace the FD with 7900 or 9000 but not sure if the 7900 or 9000 is compatible with 7800 brifters?

The 7800 series did not have a specific compact crankset BUT it would run perfectly with an odd-series R700 crankset. I had that combination.

So, there really shouldn't be an issue between 7800 FD and a Shimano compact crankset.

What you seem to be saying is that the smallest cog at the back is rubbing, then its to be expected when you cross chain. For compact, 34/50, expect the 2~3 smallest cogs to rub against the big ring when you're in the small 34 ring. Its to be expected.

A little cross chaining is not the issue it is the fact that I have dropped the chains many times and in almost every case it while I am going easy preparing for a upcoming hill. I am afraid to shift the FD for fear that I will drop the chain. It has been adjusted by three different shops on many occasions.
The last shop said that the rub in the small ring and the first cog is related to the movement of the FD. It might be a bad FD or wear but I am ready to try something else.

I thought that a 7900 FD might help though I am almost ready to go Di2.

7900 and 7950 (and 6700/6750, and 5700/5750, you get the idea) cranksets essentially had the teeth of the two chainrings farther apart than on previous generations. between the two is their composite ramp. being farther apart allowed greater small/small cross chaining before the chain would contact the outer ring. it also (with the proper front derailleur and shifter) significantly reduced the chances of dropping the chain to the inside when shifting from the large ring to the small ring.

It comes down to the limit screws and how close you set the FD cage to the rings.

Set the limit screws for the small ring as close as possible without rubbing on the biggest cog.

Note that 7800 shifter have an indent for half shift for the front not found in the 7900 shifter.

-In setting up the FD, release the cable.

-Release ALL the indents on the front shifter.

-shift the rear cogs till the biggest.

- Set the FD cage as close to the chain ring as Shimano recommends. Which is approximately 1.5~2mm of the tallest teeth. Ensuring that the flat portion of the cage is parallel with the outer chainring.

- Chain on small ring, adjust limit screw while turning the cranks till the chain rubs and then turn back that half a milimeter.

- Clamp up the cable for the FD and adjust again.

- Adjust the outer limit screw by shifting to the big ring and rear smallest cog. Till the point the chain rubs and turn back another half a millimeter while turning the crank.

Run through the process, it should work out fine. (Hope I have not missed out anything important. )

yes, you missed the part where the rings are too far apart.

What has that got to do with the chain dropping when shifting into the smaller ring?

Logically, that should be associated with the chainrings being too close together.


On a side note, you could get a K-Edge chain guard to help in minimising the possibility of chain dropping if all else still fails. (Maybe that's why there's a market for them).

I am going to change the FD it has been adjusted many many times and I still have issues!

Questions:
1) Will a 7900FD work with 7800 shifters? Will it work better than 7800 FD?
2) Will a 9000 FD work with 7800 shifters? Will it work better than 7900 FD?

Before you do, have you adjusted your chain length ? Assuming you changed from a normal 52/53 crankset to a 50T crankset?

Di2 is made for you !

I'm very interested in the 9000 front derailleur because of the support bolt feature. The hanger on my Cervelo R3 SL flexes a lot when trying to shift under load. I've tried 7800, 7900 Red Yaw, and old Red front derailleurs to no avail. Hopefully the cable pull of the 9000 derailleur will permit the use of my Red shifters.

The chain was recently replaced.

Cannondale is showing their new crank with DA900 Mechanical FD. Can we assume that it will be compatible with most cranksets then.

I am hoping to run Praxis rings on Hollowgram SI SL cranks and a 9000 groupo

http://www.cannondale.com/2013/bikes/ro ... e-crankset