Snyders has a good brake centering tool on page A-96 part number A-2020 price $39.95. It works great, I've got one. It is best to first adjust the rear brakes with the tires on the floor. and the brake rods disconnected . The reason being that the rear shoes are placed different than the front shoes. On the rear, you've got a shoe on the top and a shoe on the bottom, instead of a shoe facing forward and a shoe facing backward like on the front. On the rear the brake cams float in the brake camshafts. The floating rear brake cams on the rear were designed to allow for wear on the rear axle housing bearing races. When the rear wheels are on the ground, all of the clearance between the rear hub roller bearings and axle housing race is taken up. If the rear brakes are adjusted with the rear wheels off the ground, When the wheels touch the ground, the clearance between the bearing rollers and bearing race will be taken up and can and usually do cause a drag on the bottom shoe. This will cause the rear drums to get very hot. The rear axle housing bearing races carry the weight and do wear. The bottom of the axle housing races need to be checked for wear when the rear hubs are off. The housing races can be turned down and a sleeve pressed on to repair worn axle housings. If the housing races aren't worn too badly you can still have rear brakes if they are adjusted with the wheels on the ground so that any drag can be felt as the adjustments are made.
It is good or almost necessary to grind a taper on the leading and trailing ends of the brake lining. When the lining is riveted to the shoes, the leading and trailing ends of the brake lining tends to kick outward causing a drag against the drums on the ends. If a taper isn't used on the lining, it may be difficult or impossible to get the drums to pass over the brake shoes, even with the adjustment wedges backed off all the way. Here is a picture of how I taper the ends of the brake lining.
