I have noticed that a few of the Bachmann steamers that I possess have an occasional driver or wheel set out of gauge. Aside from using two small screwdrivers to kind of pry them back to the proper gauge, is there any tips or tricks that make this easier? Are there any cautions? Thanks.
That's what I have done in the past. Just be careful and go a little at a time, alternating front to back so to prevent getting the wheels askew.
In my experience, it's even more awkward trying to press them closer together.
For tender/pilot/trailing truck axles, I'll remove the from the truck if I can, and then press from the INSIDE. Most screw drivers won't span the gap between the backs of the wheels, so I will lightly grip the axle between the wheels with a pair of pliers (parallel jaws are best, not tapered needle noses) with the pliers against the back of one wheel, and then use a small screwdriver wedged between the pliers and the other wheel. Slightly twisting the screwdriver will wedge the wheel out. Again, go slow and careful!
And once done regauging, make sure to put a small drop of superglue (or your preferred plastic-safe adhesive) on the inside of the wheel, spreading it evenly around the axle to hold it in place. Just make sure to let it dry before putting the axle back in the train.
I use only one screwdriver usually against the frame and the Driver, and do as @DaveGard does.
As he states "go slow and careful".
I find baby steps are best.
Also check with your NMRA Gauge as you rotate the Wheelset/Driver 360°, assuring the wheel backs are parallel to eachother and square to the railhead.
Good luck