Not many Chevs of the mid 50's had straight air. And straight air is the only way to go if you're going to pull a trailer. Vacuum trailer brakes were almost a thing of the past by the mid 50's because they were so undependable. Most of the time you had no brakes. But those were totally different times. If a driver only piled one truck up a year, he was considered a rather safe driver. But today that is totally unacceptable. I hauled grain and gasoline with a sister to this one back in the 60's.
https://plus.google.com/photos/108197707187186692269/albums/5833890633528587697?hl=en-USIts a 55 GMC that was born with straight air. Air valves can easily be retrofitted with modern valves and it will stop just like a new truck with the exception of not having ABS. Air brakes are actually the simplest type of brakes there is and they really haven't changed much in the last 50 years except for ABS which really only becomes a factor on slick pavement.
