Removing the valve is just like removing any other brake system component. the most important part is removing the lines without damaging the hex head fastener.
To do this, get some WD40 or even better is PB Blaster. Spray liberally on the hardware and prevent from getting on painted surface and prevent brake fluid from getting on surfaces as well. Let soak and wipe off and repeat and if possible allow to soak overnight. Use a flare wrench to remove fitting that is correct size for fitting. The fittings are soft and will strip. So, if you don't use flare wrench use high quality wrench that is open to five points and not eleven just like a cloased end six as opposed to a twelve point as the five point will flex less.
Slowly remove fitting with a rag underneath to prevent fluid from getting onto paint. If it does remove with paint safe cleaner.
Cover each line to prevent contamination from getting in. Then remove valve mounting bolts.
I have attached diagrams to show location and what valve looks like. One diagram shows how to remove Master Cylinder Lines, same Teechnique, and proportioning valve is visible on left.

Answered by DrCranknWrench (expert)
3,292 answers provided