Brake boosters for the Ford Explorer don't typically need replacing. However, if you press on the brake pedal and the pedal goes all the way to the floor (and there are no fluid leaks), that's a good indication that your booster has failed. The brake booster on the Ford Explorer is mounted to the firewall in the engine bay. You'll need to remove the master cylinder to get to it. If you've never done this job before, you'll need to allow yourself at least an hour to get through it.
Mark the brake lines coming into and out of the master cylinder using masking tape and permanent marker.
Orient the tube wrench so that it grabs the end of the nut by first sliding it over the brake line.
Pull the brake lines out of the master cylinder.
Unbolt the two bolts that hold the master cylinder to the brake booster.
Slide the master cylinder off the brake booster.
Remove the bolts that hold the brake booster to the firewall.
Remove the cotter pin from the pin holding the back of the brake pedal to the master cylinder.
Slide the brake booster to brake pedal pin out of the mounting bracket.
Pull the brake booster off the firewall.
Install the new brake booster. Installation is the reverse of removal.
