This is 6870?
Trim is the very last step in setting up the front derailleur. Everything else has to be correct before trim is set. If you can't get it to the correct trim setting then something else is wrong - initial mounting of the derailleur is not correct or high/low screws not correct.
We need to make sure the derailleur is installed correctly before any adjustments are made.
Start by centering the derailleur. There are 25 trim positions. Put it in adjustment mode and move the derailleur all the way to one side. Just hit one paddle on the front shifter until it is all the way. Once the derailleur is all the way to one side then move it 13 steps in the opposite direction by using the other paddle on the front shifter. Now the derailleur is in the center trim position and you can begin.
Make sure the derailleur is installed correctly by using the procedures on page 26 to 29 of the 6870 dealer manual at
http://si.shimano.com/pdfs/dm/DM-UL0001-03-ENG.pdf. Make sure the derailleur is positioned correctly relative to the large front ring, that the backup plate is used if needed and that the support bolt engages the backup plate or clamp properly.
Then set low/high (also called low/top). Low and top screws are shown in the dealer manual linked above. See pages 69 to 73.
- Put the front on the small ring and the rear on the largest sprocket.
- Adjust the low adjustment bolt so that there is 0.5 mm between the chain and inner plate of the derailleur.
- Put the front on the large ring and the rear on the smallest sprocket.
- Adjust the top adjustment bolt so that there is 0.5 mm between the chain and outer plate of the derailleur.
Only now can trim be set.
- Crosschain big/big
- Press the button on the junction to enter adjustment mode. It should be solid red.
- Adjust trim so that there is 0.5 mm between the chain and inner derailleur plate. The chain should not rub the inner plate when crosschained big/big.
- Take it out of adjustment mode.
Done. It should work properly now. Let us know.
-Tim-