If you pull the lines off the late Toyota master and look inside, you'll see some copper fittings inside. My guess is that would have to be the check valves, though its hard to say without the manual for whatever vehicle was equiped with these masters, maybe an FJ80? You should check with JT Outfitters again and make sure that that cylinder is appropriate for a rear drum setup, I thought it was 4 way disc only.
Anyway, I still think your problem is most likely at the rear brakes. I'd check all your old cylinders for free travel and then swap them in and make sure your adjuster and the rest of the hardware is free of rust and debris and then give it another good bleed. Swapping the drums is a good idea too. Lots of drums and discs come from China now and are out of round. I always get north American cast iron, or chuck it on the lathe and check for out of round.
One other think I forgot, did you bench bleed that master when you installed it? I hear its very hard to get all the air out of the system if you skip that step. If you haven't done it, just use the kit I loaned you to make some short lines that turn back into the master cylinder resevoir and pump the hell out of it till you are free of air bubles and then reattach the front/rear lines and bleed again.
Last edited by frontrange; 09-07-2008 at 10:44 AM.