I have a 03 xlt an th brake pedal was going to th floor.so l bleed them had a good pedal drove it for two days no problem then to day was in a lot stop and go traffic and it started leaking down again I can pump them and they will hold great.anyone had this problem? I'm not losing any fuild.

 

Replace your rubber brake lines on the front brakes. A lot of times the rubber will break down on the inside and you won't be able to tell from looking at them. They're fairly cheap to replace, should be able to do both of them for about $40.

 

Thanks danger.I'll check it out.

 

Classic brake master cylinder failure symptom.

 

+1

 

And if you decide to replace your front brake lines you can get braided stainless lines for about $55. Big improvement in brake feel and will outlast your truck.

 

Is there any way u can check th master cylinder to see if its bad?

 

Bleed the brakes with the engine running as this will also bleed through the abs system...I had the same problem and this worked great for me

 

https://www.f150forum.com/f6/brake-p...-150-a-157374/

I would check your ABS HCU with a paper clip as described in this link before you buy a new master cylinder. I too thought the sinking pedal was a MC, but for me it turned out to be the ABS HCU.