splitting tree

I have a very large tree that is forked about three feet off ground. One ouf the forks is about three feet in diameter. They are pulling apart from each other. Can anything be done to stop it from getting worse

I would guess an arborist would say to "cable" the tree with a turnbuckle? I have seen this before, not sure how it is down with such a large branch, also not sure how much stress this puts on the tree when you are drilling a 1" or so hole thru it!

I have seen large trees bolted thru to hold them, but this is best left to an expert. It requires a hole to be drilled thru and then a HD all thread run thru and LARGE washers put on, then tightened. The one time I saw it done the arborist first strapped the tree using 3 or 4" wide ratchet straps and pull as much as he could. I think he used 3 of them, above the bolt location. Then he drilled the hole for the bolt. The washers he used were very large and heavy. I think the bolt might have been 3/4" or 7/8". He then drew the nuts tight, both ends of the rod, tightened the straps and did this back and forth, nuts, straps, nuts and so forth. Then he slowly removed the straps, double nutted the rod ends and cut the excess off even. Then he used a pointed punch to lock the nuts from turning. The rod might have been SS or alloy, I don't know. This was done in the late 50's on a large silver maple in my grand parents yard. The tree was then removed as it weakened further in the mid 90's, bolt still intact and not rusted on the outside. The rod ends were still visible but only a little of the outter nust could still be seen, even the mature tree had grown to almost cover the nuts.
Dave

maple flats has the right idea...3/4 inch should be big enough. really depends on the size of the tree, it doesn't have to be a bolt that big. the most important is a properly installed cable or multiple cable in the crown to support the crack. without the cables in the tree there is to much motion up above for the brace rods. a cable should be installed 2/3 of the height above the crack. those cables should be installed first.