Yep, it's called a "Surge Brake"
Surge brake system
A surge brake system is entirely self-contained on the trailer and is activated when the tow vehicle decelerates. The momentum of the trailer pushes the surge brake housing forward. This drives the push rod that is connected to the coupler into the master cylinder. Brake fluid is then forced out of the master cylinder into the wheel cylinders or pistons that apply the trailer brakes. The entire activation process is completed in less than one second. Hydraulic surge brake systems can be used by a variety of tow vehicles and can accommodate a variety of trailer loading conditions without requiring any type of adjustment. All U-Haul braked trailers use a surge brake system.
Thanks... that was the name i was looking for! I am always on the go.... so did not have time to look for it :smile: .
I have the Equalizer 4 point system for our 3000 pds Gazelle and what a difference! Nice to know the dry weight of the trailer but after you put all you stuff.. the driving is not the same! We dry camp a lot so just the fresh water itself adds a lot of weight!