Hello thanks for using 2CarPros, has the brake fluid ever been replaced since you've had the truck? It is a good idea, if the fluid is black in the master cylinder, then bleed the master itself so that none of that old fluid goes into the ABS module, then refill it with new fluid and bleed the whole system. Start with the wheel closest to the master cylinder (so the front drive side) then the passenger side front, then the drivers side rear, and last the passenger side rear, since it's the farthest from the master cylinder. This way all the air will be able to escape. There should also be 2 bleed screws on the abs module, bleed the one closest to the firewall first,then the other.
this guide should help
Please run down this guide and report back.
Monday, August 31st, 2020 AT 11:15 AM