is it safe to put trans stop leak in your brake system?and why?
No, do not put anything other than brake fluid in your system. Each brake component has rubber seals and or o-rings. Adding anything other than the approved fluid will cause damage to these rubber items . It can ruin your entire system. Fluid lose is probably in the master cylinder or wheel cylinders (if you have rear drum brakes) I recommend you find the leak and fix it properly. Your and our lives may depend on it.
No, it is not safe because it is not for brake systems. If your brakes are leaking fluid, meaning you can visibly see moisture that is brake fluid, then you need to repair the leak. Leaks can be from rusted metal lines, dry rotted rubber lines ruptured seals in master cylinders, wheel cylinders, or caliper pistons. Don't try to use stop leak.
The only safe thing to put in your brake system is brake fluid. Brake fluid is specifically formulated to give safe, reliable performance out of brakes, and is designed to withstand the tremendous heat, pressure and corrosion resistance required to keep your brakes in safe working order. Why on earth would you want to put transmission stop leak in a brake system? ANY leak in a brake system is potentially dangerous, and should be repaired immediately.