On my 50" deck's, the caster bushings and shafts are pretty sloppy, so I decided to renew these and it ended up being pretty straightforward to do.
The caster shafts are just 3/4" bar stock. I ground the weld off on the top and the shaft came right out of the wheel yoke. It was worn down quite a bit and I just wanted to replace the shaft.
Without a fixture, I just tapped in a long 3/4" bar and using that longer shaft, it was easier to tell whether it was straight when I started welding the new shaft in place. Once welded, I just cut the shaft off to the correct length.
For the bushings, I found that bearings from bronzebushings.com fit perfectly. I drove out the old bushings, and then used a 1 1/16" adjustable reamer to just clean up the bore in the front carrier so that the new bushings wouldn't hang up. The bottom had ridden on the caster and galled it up a bit so I was really only taking off any high spots.
I ordered 4 x FF1010 Oil Impregnated Bronze Flanged bushings 3/4" ID and 1.0625 OD x 1.1875 OAL. They drove in with a soft mallet and were a really nice fit with a new cold rolled 3/4" bar. The bushings were about $5.50 each to my door.
I'm really happy with the way this worked out.