Big Gray Truck - Part 1 - So you didn't want all of the brakes?

I wish this was my setup.
Image: Ford (https://www.riverbend-ford.com/research/ford-f250-towing-guide.htm)

Several Months after Part 0 of my big gray truck ownership I started to run into some high mileage issues with my truck. As this was the cheapest truck in the area that wasn’t all clapped out this was to be expected

My commute to work is about 45 minutes. It consists of about 20 mins of two lane roads which leads to four traffic circles then 5 miles of four lane highway with traffic lights to about 10 miles of interstate driving. It was during a morning commute to work that this story begins

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I was driving the truck to work and made it through the traffic circles. It was here that I noticed that the truck felt a little slower than usual. This is hard to discern as 300 hp in a 6500 lb vehicle isn’t exactly fast. As I got onto the four lane divided highway I had to slow for traffic. The truck was even more sluggish at this point. I continued for another mile before the engine really started to struggle and pulled over to the side of the road and stopped.

There was no smoke from the engine but there was the slight scent of brakes. I hopped back in to try to limp it home and discovered that the truck wouldn’t move. In drive it would load up like the parking brake was on. The parking brake had released in the morning and I hadn’t hit the pedal so there was no reason it should be on. Pulling the release handle lead to the same symptoms. I was stuck on the side of the road.

A tow truck was dispatched as I explained to my patient boss that I was going to be extra late that morning. As the tow truck operator loaded the truck onto the flat bed none of the tires were really spinning. Something was locking the brakes.

We arrived at the house and when the tow operator went to unload the truck all of the tires spun freely. A quick trip around the neighborhood confirmed that everything was operating normally. Not wanting to chance it again I borrowed the wife’s car and headed into work.

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It should be noted that I had replaced the brake pads and rotors and bleed the system about a month before with the help of a friend. About a week prior to this I noticed that the brake reservoir was low. The friend thought he had filled it but wasn’t sure. I added more fluid and thought nothing more of it. This truck came with vacuum assist brakes.

The next morning I decided to take the truck to work again. I had the same symptoms not 200 feet away from where I had them the day before. Once again a tow truck was dispatched and the truck taken home. Frustrated I left the truck and went to work.

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When I arrived home that night the truck acted fine. Hmmm. This is odd. Could the master be sticking and then releasing with the bouncing from the tow truck? With this theory in mind I dove in to removing the master cylinder. As soon as I unbolted it from the booster brake fluid began to pour out.

The master had leaked about 2 quarts of brake fluid into the booster. As I hit the brakes driving to work the vacuum was not allowing the master to return all of the way back slightly applying the brakes. Every time I hit the brakes the plunger would get stuck out a little further. The drive home on the tow truck was enough time for the vacuum in the booster to bleed off and the master would pop back to its released position.

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While I appreciate the time and effort that the engineers put into these vehicles I won’t miss an opportunity to upgrade parts to something more powerful or useful if I can. The diesel trucks came with a Hydroboost brake assist instead of the vacuum assist. While vacuum assist can create pressure in the 900-1200psi range a Hydroboost setup can apply pressure of 1400-2200 psi. This allows for greater braking force.

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Some Google-fu later it looks like it is a direct swap. The power steering pumps are the same vacuum to hydro so all I would need is the pedal, master cylinder, hydroboost actuator, hydraulic hoses and a new dual return reservoir. While the 5.4 wasn’t offered with a hydroboost setup the hose for it is readily available.
Everything bolted up perfectly. I had the remove the pulley to the pump in order to get the line on because the pump sits right over the cross member. I bleed everything and the brakes have been trouble free ever since.

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