This is a successful modification I made to the left-hand gauge wheel bracket on 
my Craftsman 42" mower deck.  It allows the gauge wheel to deflect inward when 
you brush against a tree while trimming close with the left edge of the mower 
deck.  After straightening my bracket a few times, I decided to re-engineer it.  

Basically, I removed the bracket and cut it in half along the (roughly 45 
degree) bend that makes the portion of the bracket with the gauge wheel mounting 
holes run parallel to the mower.  I then modified a 4" heavy-duty spring hinge 
so that it mounts behind the bracket.  The modifications required included a 
roughly 1"x1" cutout in the front lower hinge plate so that the mounting plate 
on the mower deck fits flush against the back of the bracket.  Without this 
cutout the hinge plate interferes.  It's hard to see, but it's just visible in 
the right bottom corner of photo MowerModBack.  I also chamfered the top corner 
of the hinge plate that is exposed, to make it less sharp.  Holes were drilled 
in the hinge plates where needed, although I was able to use three of the holes 
already in the plate.  

I mounted the hinge with 1/4" machine screws and nylon-locked jam nuts.  Two of 
them needed to be placed in the opposite direction to clear the gauge wheel.  A 
total of six bolts seems to adequately support things.  I also added an 
adjustable stop plate that prevents outward movement just at the point where the 
gauge wheel is tracking forward.  This is visible in the other three photos and 
was made of scrap plate with a slotted hole to allow adjustment.  

Once it's all assembled, you adjust the spring tension to strongly push the 
wheel out against the stop.  If you hit a tree or other object, the wheel just 
moves out of the way and then springs back.