How to remove rear brake drum on tandem truck?

Answer 1

Chock the wheels, release the brake, ensure you're not going to get run over.
Back off the slack adjusters.. if you have Haldex slacks, it'll be a 7/16" socket or wrench.. if you have Bendix slacks, it'll be a 9/16" wrench or socket, plus a screwdriver or set of sidecutters to pry up on the release lever. Adjust the brakes to the released position (away from the brake drums). Then you can remove the drum... if it doesn't just slide off, give it a couple whacks with a hammer to loosen it.
If you can't supply air to the emergency chambers for whatever reason, you can cage the brake chambers with the bolt attached to the brake chamber... you need a 3/4" wrench to do this, and, unless you have a specific brake chamber caging socket, a socket won't be deep enough to cage them fully (although you just need to cage them enough to be able to adjust the slacks).