I've got little time - deadline today. However something similar came up on another board recently, so I'll just post that question and my response below. It's basically the reverse to your question, but I'm sure you can figure it out from there. Anything else or more clarification, ask & I'll respond tomorrow.
Not so long ago I was replacing the high E string and retuning my guitar when I noticed that the bridge wasn’t perfectly aligned. The right side of the bridge (where the tremolo arm is) is a slightly lower than the left side.
Now I’m suspecting this has to do with the tension of the springs. When I replaced the strings for the first time, the tension of the strings was so high I had to tune my guitar to Eb in order to keep the bridge parallel with the top (even tightening the screws in the cavity didn’t help). A few months later, when I replaced the strings for a second time, I decided to add a 4th spring (and arrange them like this: II II) so that I could tune my guitar back to standard E.
However the bridge of my guitar may have been set up like that since the beginning. I have this guitar for almost 2 years now and so far I’ve never had any real issues with it. The guitar stays pretty much in tune and I only have to retune it occasionally.
Hence my following question(s): Should I leave the bridge the way it is, should I rearrange the springs (like this I\II for instance) or should I adjust the action on the right side?
Thanks in advance
And my response:
Even changing from D'Addario to Ernie Ball strings will make a small difference in how level the bridge is - EB strings are much higher tension. But it won't be a huge difference. You probably upped the gauge too - that's when you see the real difference in a Floyd.
Now... where you went wrong was to tune down and then add a spring to pull the bridge flat. Both will work but have side effects. Tuning down is obvious - different pitch, a floppier tension and softer attack to the tone. An extra spring makes the trem action stiffer - it takes more force to stretch the springs and move the trem. A "good" (or bad, depending on what you like) side effect of this is the bridge is more stable, less likely to flutter, won't flatten notes as much when you bend one string in a double stop and will be less prone to accidental "whammage" when you palm mute.
The usual way of levelling the bridge is to tighten the screws holding in the spring claw. Tune down a bit (it'll raise in pitch again as you tighten the springs and the bridge pulls back, and prevents putting unnecessary stress on the strings), tighten the springs and repeat until the bridge is level at concert pitch. This keeps the trem action all floppy the way a Floyd is supposed to be while levelling out the bridge.
What you describe - the bridge being lower on the treble side than on the bass side - is not related to spring/string tension. It should be that way - the radius on a Floyd is fixed, with no height adjust for individual strings. A guitar usually has lower action on the treble strings, and the way you do this on a Floyd is to lower the bridge on the treble side (via the hex nut in the pivot post), so the treble side of the bridge is always lower than the bass.
The only other thing to check is that your knife edge is sitting in the v of the pivot post properly - they sometimes pop out when you change strings by removing them all at once.