Not hard at all. Definitely don't hammer anything, you will ruin the bearings in the gearbox.
First, make sure the tension pin is out of the coupler. Second, make sure the master spline (the thick one) is lined up, there is a notch on the coupler where the master spline is.
Third, wire brush the splines on the steering box. Then get a cylindrical steel wire brush about 1/2 to 3/4 inch in diameter and do your best to clean out the splines in the coupler; you may have rust build up in there. You can use a battery terminal brush in a pinch. You might try to let it soak a bit in Liquid Wrench or WD-40 before you brush to break up any rust.
Of course, check the splines carefully for any signs of damage: nicks, gouges, etc.
Bob
AAR 4-speed 3.91, Tor-Red;
70 440 6 pack Roadrunner 4-speed 3.54, Plum Crazy;
68 Formula S conv 383 4-speed 3.23, Electric Blue;
69 Barracuda conv Slant 6 OD4 2.94, 71 B5 Blue;
78 Lil' Red Truck, Red;
70 Challenger S/E. 505 6 pack, Passon 5-speed, 3.55, B7 Blue
| 
