I saw a F450 today that had a 40 foot livestock trailer that had air brakes on the trailer. Not the truck just the trailer. Glad hands mounted on the headache rack just like a semi. I didn't get any pix. Has anybody ever used/ seen a setup like this before? Truck was parked at a farm and noone was around for me to talk to cuz I sure have questions. Did some web surfing and I can't find anyone who makes or sells anything like this.

it might have been vacuum over hydraulic. that is what i use and it takes 2 hoses.

ya that was my thought when i first read the OP its a vacuum system I have used a F-450 to pull hay out of a field before I had my own trailer it was a good system but the guy that owned the truck said he had problems with it often so not real sure on if its a great system to use but it could of just been the guy that drives the truck for him regularly didn't know how to use the system very well because they just got a new truck and it has the same setup on it

How does it work?. Vac pump on the truck engine to assist something like a diapghram/surge brake on the trailer?

they include a control valve, vacuum tank, vacuum / hydraulic actuator, vacuum hose, and hydraulic brake line kit. actuator on truck, tank and control valve on trailer. they work very good. i pull a 32' triple axle cattle trailer and a 40' dual tandem gooseneck with the vacuum over hydraulic setup and they perform excellent. they beat the electric brake setups i have used by far.