Brakes Hitting Floor. No Pressure

Want an educated guess?

You let the master cylinder run dry and now the master cylinder needs to be bleed as well.

The master cylinder bleeding procedure is different and separate from the wheel cylinders. It can be difficult (sometimes impossible on some cars) to fully bleed a master cylinder on the car because it's not level. There usually a procedure to bleed the master cylinder on the bench before installing on the car. YMMV

What I usually do when the brake system needs to be open for an extended time is to block the brake pedal partially down with a piece of wood between the pedal and the car seat. Either remove the brake light fuse or the battery to keep the brake lights from discharging the battery. When the brake pedal is partially down this covers the master cylinder refill port holes thus preventing all of the brake fluid from leaking out.

wmburns said:

Want an educated guess?

You let the master cylinder run dry and now the master cylinder needs to be bleed as well.

Click to expand...

I'm thinking if that happened and he has ABS there will be air trapped in there too.

ABS systems are notoriously difficult to bleed. You may have to resort to a "power" bleed system.

This sounds right, try to dig out Factory Manual and verify.

For the 2002 and earlier Mustangs without Traction Control, the ABS valve block or pump and motor assembly does not require any special bleeding procedure. For the 1998 and earlier Mustang ABS systems, there are NO Special Procedures or Considerations in bleeding the system.
For 1999+ Mustangs, with Traction Control, you SHOULD use a bidirectional controller when the ABS controller, MC, or any line between the two the Master Cylinder is replaced or opened. However, NO MUSTANG requires any type of ABS (or ABS/Traction Control) control when just the calipers or soft lines are replaced. Again, for those with traction control, the MC MUST NOT GO DRY.

You might need to rebuild your master cylinder. If you can pump the pedal higher, it's probably air in the system. To test the master cylinder, determine the position of the depressed brake pedal (assuming there is no air in the system), and push with gentle but firm pressure to determine whether the pedal sinks past this position to the floor. If it sinks, that's fluid passing the internal seals and it needs to be rebuilt or replaced.
Replaced an ABS unit in a 2002 and wasn't having much luck with the standard bleed procedure until I bled the master cylinder (using the bleed screws on the mc). Once the master cylinder was pumping, the rest of the system bled as one would expect which probably included any air in the ABS as the pedal is firm and cannot be pumped higher. I had read 'start with the master cylinder', and it seems that was good advice. Now how about a trick for you just in case all the above doesn't improve your pedal.
If you jack up the rear and run the engine in gear, the ABS pump thinks the tires are slipping and starts running. Any trapped air in that area should bleed out.