Jimmy,
Please excuse me if I'm misunderstanding you, but are you talking about the tension control knob on the right side of the reel? If that is what you are talking about, that's not the mechanical brake.
To access the mechanical brake system, hold the reel and unscrew the long screw on the top of the reel - it's on the right hand side at the top of the side plate, just slightly forward of centerline of the reel, forward of the Abu logo. Here is a picture with my right index finger pointing to the screw:
After unscrewing that, hold the reel with your right hand and turn the left sideplate clockwise:
Then pull straight up on the plate to expose the reel spool and mechanical brake system:
To adjust the brakes, push them towards the inside of the spool to turn them off, or pull them out to turn them on. Remember - in = off, out = on.
Note that the above picture has two on and four off. I believe that is how they come from the factory. I'd recommend pushing out four and leave two in. Best practice is to set them in pairs - across from one another.
After you adjust them, replace the side plate and rotate counter clockwise to set, and then tighten that screw again.
Put the lure on that you are going to use, and let out about a foot of line. Then tighten that tension knob that I think you might be referring to until it's slightly "snug". Hold the rod out in front of you, tip slightly up. Press the clutch lever / casting bar. The line shouldn't move. Slowly back off the tension knob until the line starts moving and the lure heads to the ground. The reel tension should now be adjusted perfectly to that lure. If you switch to a lighter lure, it might need to be backed off a bit. Heavier lure - might need to be tightened a bit.
I sincerely hope this helps. If the tension knob was not what you were referencing, and you actually were adjusting the brakes and not getting any satisfaction in the backlash fight, then I'd say you might have a problem reel.
Please let me know if you get it adjusted via this method or if I'm off base.
All the best,
Glenn