I replied to a different thread about brake pedal fade, but would like to document my issue here as well in hopes that it helps someone else out.
Condition: Brake pedal fades to about 25% of its range of motion when stopping. The issue is most notable when slowing to a stop, it requires additional pressure to stop as the pedal fades to the floor. The truck will stop and hold. Also, the ABS works properly. When braking at speed or on the highway, the issue is hardly noticable.
Diagnosis: So far I have had the system bled twice, without much or any noticable improvement. The tech working on it says it's probably the master cylinder. I kind of agreed, however I thought if it were the master cylinder the system would leak all the way down, not stop at a point like it is currently doing. The technician working on my truck is my friend, he is knowledgable, however, he doesn't work on Fords all day. I called my friend that works at Ford to get his opinion. He says it could be a master cylinder and also he has seen the ABS hydraulic control unit (HCU) go bad, essentially causing some of the brake fluid to enter the ABS system under normal braking.
I did some research on the issue, it seems like a pretty common problem. It seems like a lot of folks with the problem replaced a few master cylinders before diagnosing the ABS HCU. Here are a couple of the links I found in my research.
Today, based upon what I read, I checked the ABS HCU. The unit is generally located near the master cylinder, below the air filter. I removed the plugs off the two lower ports, on the firewall side of the part (the ports are below the brake lines, you will have to feel around for them). I fashioned a paper clip and inserted in the driver side port. While the truck was running (and me holding the clip), a friend slowly braked. The valve had at least a half inch of movement towards the firewall. Based upon what I have read, this is a sign of a bad ABS HCU.
This is what the ABS HCU looks like:
The numbers on my part are:
Number/Code below bar code: TRW EHCU 13975507B (Not sure what this means)
Ford Part #1L34-2C346-AA
Ford price on the part lists for $710, fordparts.com has it at my dealer for $575. At this point, I am going to try and order a salvage unit from LKQ or on ebay. There is a parts seller on eBay selling new units, free shipping for $225 and comes with one year warranty. I saw one on LKQ for $150 that is a salvage and you could purchase up to 24 month warranty for a reasonable price.
Sorry for the length, I hope this helps someone out with this issue. I will post an update when I get the new part on my truck and the issue is resolved.