If the motor of my 2007 6.0 isn't running I immediately have no power brakes, and it takes a lot of leg pressure to slowly stop the vehicle. I was towing my 5th wheel with my 12' utility trailer behind it and I had a belt idler loose it's bearings and it spit the belt off, leaving me with no boost while I was going about 65 MPH. It took forever to stop by just using the brake pedal (afterwards I realized that I could have applied the trailer brakes manually and had more stopping power). I have a total trailer weight of about 12,500#. Today with just my 5th wheel, I realized when I started off that I hadn't turned the engine controller down to a tow setup. I moved the transmission selector to neutral and applied the brakes. Then I shut the engine off and when I did the brake pedal immediately became nearly ineffective and I had to push firmly to hold the truck and trailer (abt 9,000#) stopped on a very slight grade.

The hydro boost has what looks like an accumulator. Shouldn't this give some power brake for a little while? How do your trucks act?