We have f800 water truck with the hydromax brakes, it started early this summer with the brake pedal slowly moving to the floor as you applied them, if you jabbed it it would stop but let off and it would slowly go to the floor. I replaced the master cylinder with a brand new napa unit, not a reman. I bled it and it worked well for a while then all the sudden you would push the pedal it was to floor, we tried bleeding it more and more, no dice. I thought i had a bad unit so the exchanged it. This unit worked a while then i hit the brakes and felt something funny then it went righ to the floor. with the caps off the master cylinder, if you hit the brakes the fluid gurgles and shoots out. What am i missing? I am new to working in these brakes and would appreciate any guidance! Thanks

 

Is that a Bendix or Bosch or something else system?

How are the lines,hoses and wheel cylinders? Brake shoes, drum thickness?

I found a Bosch manual on line, but can't get it to load. Are you working off an OEM manual?

Is this the same system?

https://www.ford-trucks.com/forums/9...lp-please.html

 

I an not sure on those brands, lines and hoses all are in good shape, i replaced all the rubber lines in the front including the lines between the cab and frame. I do not have any manual at all i have went off of what i could find online.

Yes i have the system described in the thread, other than this master cylinder issue the pump motor works and kicks on as it should, the pedal also goes to the floor with the electric back up as well, it is like someone has broke inside the master cylinder.