Air over is not straight air. It is merely a booster similar to vacuum boosted brakes. The foot pedal may not be tied into the trailer brake circuit. Most air over systems had a completely separate braking system on the tractor and the trailer. A trolly valve on the steering column controls the air to the trailer. If it is two separate systems, extreme caution should be used when pulling a trailer on slick roads. It was common to see this model trucks with a back corner bashed in from a jack knife. With full air, apportioning valves and ABS, the work jack knife has almost been removed from our vocabulary. While pulling a trailer, especially one that caught a lot of wind, this truck would have been lucky to 4 miles to the gallon.
