MC residual valve?

Ok so I read about half the posts on here but I still haven't found a definitive answer on wether there is a residual valve in the stock 74 disc drum master cylinder. I put rear disks on so now have 4 wheel discs but after bleeding brakes I have quite a bit of drag on the rear. Just wondering if there is a valve built in to the master cylinder I am not useing a proportioning valve. It's a dirt track race car.