Sorry you had to do this - I was hoping you could get by without dropping shaft. Hey, at least you have a garage floor - mine work area is gravel, under a carport.

I loosened nuts, not u-joints.

Like Mark says, the nuts are held in place by a metal clip that must be "peened" back. The lip is bent around the nut so the nut won't move.

You can bend them back with a screwdriver so they are flat, then attack with your 17mm box end and a big flat-blade screw driver wedged in the ujoint as backup.

If you are actually dropping the driveshaft, you may have to remove the emergency brake spring bracket like I did.
If it gets to that, turn the adjusting nut until the spring is loose,
remove one of the two bolts holding the bracket in place,
and you should have enough room to clear.

Good luck,
Joe