Shimano Deore XT FD-M8000 Dealer's Manual

To adjust the tension, use the barrel adjuster to fine-tune the cable tension. Turn it counterclockwise to increase tension and clockwise to decrease tension until the shifting is smooth between gears.
The derailleur should be aligned so that the outer cage plate is parallel to the chain. Ensure there is a 1-3mm gap between the bottom of the outer cage and the top of the largest chainring.
Check if the derailleur is properly aligned and that the limit screws are correctly set. Adjust the high and low limit screws to ensure the derailleur does not move too far outward or inward.
Inspect the cable tension and adjust as necessary. Lubricate the derailleur pivots and check for any dirt or debris in the mechanism. Ensure the derailleur hanger is straight.
Ensure the high and low limit screws are properly adjusted. Check the alignment of the derailleur and that the chainring is not worn or damaged.
Regularly clean the derailleur to remove dirt and debris, and lubricate the pivot points. Check the cable for wear and replace it if necessary. Ensure all bolts are tightened to the correct torque specifications.
First, shift to the smallest chainring. Then, loosen the cable anchor bolt and remove the old cable. Thread the new cable through the shifter and derailleur, and secure it with the anchor bolt. Adjust tension as needed.
You will need a 5mm Allen key, a Phillips screwdriver for limit screws, and a cable cutter if replacing cables. A torque wrench is recommended for ensuring the correct torque on bolts.
The low limit screw controls inward movement and should be adjusted so the derailleur cage barely clears the chain on the smallest chainring. The high limit screw controls outward movement and should be set similarly for the largest chainring.
While it is possible, optimal performance is achieved when using a Shimano shifter designed for compatibility with the FD-M8000. Mixing components from different brands may lead to suboptimal shifting performance.