I replaced the calipers rotors and pads in the front and rear on my 2001 F350 Powerstroke. I replaced the front about a week before the rear, and after bleeding the pedal felt great. As soon as I replaced the rear, the pedal would get hard during bleeding, but as soon as I started the truck the pedal falls to the floor no matter how many bleeds I perform. Im also hearing a hissing noise when the brakes are applied and I know that can be related to the master cylinder failing, or a bad brake booster. But since the pedal felt fine before I did my rear, im wondering if something else could fix this rather than replacing my master cylinder. Any thoughts?
Assuming you are bleeding in the correct order, usually furthest first, closest last, then perhaps you need to go to a shop that uses a power bleeding machine - some vehicles are very challenging to bleed.