Questions;
What did glue you use on the original?
I can't see a split, is it the glue joint?
If the others are still OK? stick with that glue.
Most likely it was a glue starved joint?
I'd make a new one rather than take a chance on regluing the original.
I don't like gluing to old glue. You can't really remove all of the old glue unless you rejoin/resaw.

 

OK, I see the small split now.
How thin is that portion? and if it's not at least 1/4" there's not enough strength there to support a person stepping n it.
Rather than have it lay on top of carpet? I'd just make it thicker and butt the carpet up to it.
Double sided carpet tape under both will hold them both down.
I'd repair what's there IF you don't want a "do over" with CA glue and a support strip underneath.

 

It appears the threshold was on top of the carpet. The thin edge just has trouble dealing with someone stepping on the edge and it flexing. If it wasn't on the carpet it's not sitting flat on floor, you may need an adhesive that will fill the gaps. Something like construction adhesive or a polyurethane glue.

 

As Steve mentioned above, the thin edge is the problem. You need to find a way to support the thin edge. It will be easier if you have a wood floor under the carpet. I would try using flat head screws. If possible, install a row of flat head screws just behind the thin edge to support it, then install the threshold. Depending on how deep you could install the screws, you could possibly adhere a continues support, using metal or wood, on top of the screws. You could adhere a thin metal piece directly to the threshold Be careful installing the screws, they could grab the carpet fiber and pull it, causing a bigger problem.

 

I am assuming the carpet butts up to the threshold and is held in place by tack strip, and the entire threshold sits flat on the subfloor (proper methodology). I can think of a couple of repair methods. One, use CA glue and wedge the joint closed while the glue cures. Two, remove the threshold and work a good wood glue into the split with dental floss, followed by clamping and cleanup.

 

I had to cover a portion of the carpet 1 or so inches because the cats buggered up the pile next to the aluminum tack strip.

2 of the suggestions are going to be very helpful. Putting a shim under the thinnest carpet side overhang & the dental floss glue applicator.

As always thank you so much for the generosity of your time and experience.

Benji

 

If you are going to shim the underside of the threshold on the carpet side, I might suggest plywood, 1/4" if you have the space. Glued to the threshold after the split is fixed.

 

OK, I see the small split now.

2 of the suggestions are going to be very helpful. Putting a shim under the thinnest carpet side overhang & the dental floss glue applicator.

Zooming in on your photo shows that the split continues on beyond the lower edge of the photo. Your repair must address at minimum, the entire length of the crack.

 

Everything I've glued since the 1950's has held well with Elmer's . Repair a shovel handle by adding a M / Tenon section to maintain handle length . tip -- don't be concerned with tooo much glue . Size the joint and work glue to the very bottom thin area of the crack with a thread if necessary . Too much clamp pressure is often the culprit of failure with any glue especially white glues . Don't be in a hurry to clamp it .

 

It would work better to cut the carpet in a straight line removing the cat damage and glue it to the floor with some carpet adhesive. Then butt the threshold up to the carpet and glue it directly to the floor. The carpet adhesive could be used for both. If the threashold was mounted directly to the floor you couldn't break it regardless of how thin it was.