Re: Strange trailer handle?
I had a trailer that had that same set up, the lever is a parking brake, it manually operates the brake rods to lock the brakes. Mine was on a cable spool trailer, I got it from a company that did power line work in the mountains. The trailer could be parked with the brakes locked, while they reeled off cable down the road. It had two axles, both had brakes and a brake rod. The tongue can rotate some, but it tends to bind simply because it's a tight fit. They take a lot of maintenance to keep everything moving. The brake rods have turnbuckles, the brakes are adjusted both at the brake adjusters and by the rods. I set mine so that they brakes were freewheeling at the point when the reverse lockout strap was in place. There is no return spring, the brakes are the only return spring. I guess that if they had a spring, the thing would take too much force to activate?
To back up or go downhill you need to fold that strap down to prevent the brakes from engaging. The wheels on mine were obsolete, I pulled the wheels, fitted modern hubs and wheels. Mine also had some odd ball tire size that no one had heard of. Mine also had solid 2x3 steel frame rails, the tongue looked just like your trailer. It was extremely heavy but a rather small trailer, only 80 x 130" overall with a spool carrier on it when I got it. I scrapped the spool carrier and used it to haul small machinery on. I rarely used the brake set up, and removed it in favor of a pintle hitch after changing the wheels and hubs. There was no need for brakes when pulling it with a full size dump truck. I sold it with the machine that I used it for a few years ago.
That set up is most likely from the late 40's to the mid 50's. Do a search on vintage travel trailers and ask around those circles for info. I've seen several early 50's trailers with similar braking systems.