Help - Brake problem!

Hello friends, again bothering them, I have a problem with a part that looks like a valve or auxiliary cylinder that is just above the rear difference of my 1987 ram50, from there are the brake lines for the rear tires, the problem is that this valve / Cylinder is pulling brake fluid, I do not know what it's called and if they sell it, at the moment I do not have a photo available, but this piece comes as a spring with adjuster, a friend told me that it is like an auxiliary that detects when the truck Carries weight and sends more liquid to the rear wheels for better braking, someone knows about this and if they could help me, greetings!

Your friend is right, it is the rear brake proportioning valve, and it does adjust the amount of brake pressure is applied to the rear brakes as the load changes. That valve should be the same up to 1996, and you may be able to find one at RockAuto or the dealer.

Thanks for your answer, my friend, you will not find it on RockAuto, or I'm very stupid or I'm very blind ... :(