Found an article on brakes Air Brakes or Hydraulic Brakes: That is the Question - Articles - Maintenance - Articles - Work Truck
Below are quotes pulled out:
What brake system is more appropriate for a medium-duty truck's size and duty cycle?...In most cases, hydraulic brakes are used on trucks up to 26,000-lbs. GVWR.
(my note: Seneca GVWR 28,000 lbs)
"Todd Kaufman, F-Series chassis cab marketing manager for Ford Motor Company, draws the line between hydraulic and air brakes based on a truck's duty cycle, stops per day, and payload requirements. "In the lighter applications from 19,501 lbs. to 26,000 lbs., hydraulic brakes do well to serve the market. You might even stretch it as high as 29,000 lbs.; but, usually, when going above 26,000 lbs., loads are substantially heavier, which may overload the hydraulic brakes, causing them to wear sooner and diminish stopping performance," he said."
Applications: Moore recommends air brakes for heavy vocational applications and noted they should always be used in heavy towing applications."
A significant reason why air brakes are preferred in heavier trucks (above 26,000-lbs. GVWR), compared to hydraulic systems, is their robust stopping power when they work - and when they fail. For example, if there's a leak in the brake line of an hydraulic system, fluid pressure can lower to the point where there isn't sufficient force on the brake pads to create the friction needed to slow the wheel. Eventually, if the leak is not repaired, the truck can lose braking power in that portion of the system, reducing the ability to stop in the same distance. With air brakes, the opposite happens. If there is a leak in the air brake lines, the air pressure decreases, which actually activates the brakes at the wheels and brings the vehicle to a safe stop.
However, air brakes come at a premium price. According to Kaufman of Ford, the air brake system costs approximately $2,500 more than hydraulic brakes, because of the extra components to operate the system. "When you compress air, you have moisture, and you have to get rid of that moisture so you're adding air dryers as part of the initial purchase. But, if you're going to keep the vehicle for more than five years - maintenance costs tend to go more vertical after year five and get really expensive. After that, I think air brakes pay for themselves," he said.
Another factor with air brakes is how they impact a fleet's available driver pool. Even if the truck is under 26,000-lbs. GVWR, which would normally not require a commercial driver's license (CDL) to operate, if it is equipped with air brakes, the driver may have to carry a CDL, depending on the state's laws, which limits the number of drivers qualified to operate the truck.
"Air brakes, for lack of a better description, are either 'on' or they are 'off.' If you've never driven an air brake truck, the first few times you press the brake, you feel like you're putting yourself through the windshield. Unlike hydraulic brakes, which modulate more intuitively, the operator has a lot to do with actively modulating the air brakes to make the stopping process smoother. That's something the driver learns," Kaufman noted.