6 months ago I was contemplating a tow dolly or to flat tow to move the jeep around. There is nothing fun about a 800 mile journey in a CJ, I would much rather be in my Truck. I needed a solution that would not take up too much space and let me control the vehicle in a "stopping" situation. I ended up choosing a flat tow, mostly becasue all I need to store then is the tow bar and whatever I need for the braking system.
I decided to hook up the Jeep for a flat tow test, without brakes, just to see what happens, and its mostly fine, until you really need to stop, it then makes the truck wiggle all over the place, and make the ABS work harder than I have ever had it working. This confirmed my need for brakes, I just was still waiting on parts.
My options were a brake buddy/blue ox, but thoes were lots of $$ and were not controllable from the truck. I wanted a proportional system, similar to electric trailer brakes. I "invented" my own system.
Vehicle with electric brake controller
an "infinite" air source I used my air compressors in my jeep
Air storage tank (I had a total of 4ga, but 1ga would work fine)
Air hookup in cab of jeep
7 pin trailer connector with +12 acc working
2 inch bore 10' stroke double acting air cylinder. (automationdirect.com) ($85)
electropneumatic transducer 900x 0-10v 2-100psi (ebay) I have a Control Air 900x, but there are a few Manufactures. I paid $160 for a good condition used.
1 trailer magnet (Does not matter what kind/size) $40
Air Regulator (home Depot) $10
1/4 poly tubing for air plumbing/fittings/T's (automationdirect.com) $25 ish
1 emergency brake engager (etrailer.com)
Miscelaneous hardware to mount cylinder to brake pedal/tub of jeep This will vary depending on the model of jeep you have.
Function and Hookup:
My "air cylinder" is a Dual acting, meaning you can apply air pressure on one side to make it expand and the other side to make it retract. In order to make the cylinder retreate properly I hooked up an air regulaor set to about 10 psi on the "retract" side, as to be absolutely sure the brakes would not be barely dragging. in a 2 inch cylinder 2x the air pressure is the pounds of fouce, so I always had 20 lbs that was making the pedal stay "up". My Electric Regulator puts out 2 psi at 0 volts signal so I needed to have a pressure >2 psi to ensure the pedal was in the "up" position.
The brake controller needs a magnet in order to think its hooked up. I tried a simple 30 watt light, and it thought there was a short in the system. A magnet instead, and I got a simple "c" on the contorller meaning all was working well. This was the easiest way to fix that problem.
I have a teknosha prodigy brake controller, I ran it in no "boost" mode. Max setting of 4.3 volts. The electric regulator was very linear in its response, so 1 volt 10 psi, 2 volts 20 psi etc. at 60 psi the brake pedal was on the floor, and the jeep's tires would skid at that point. At 1 volt I could feel the brakes, just barely and once I got to 2 volts the jeep definately stopped itself under "normal driving conditions" If I hit the brakes hard the jeep definately reacted to that and helped get everythign to a stop.
It was nice in the windy areas where it started moving left to right to just tap that brake lever inside, and it would straighten right out. This feature right here makes this system SO much better than a brake buddy. Its also much more compact. I really like being able to control the brakes inside the tow vehicle. I used this setup on a 1600 mile trip and it worked great in the mountains and the flats on the interstate. It does have a 1/10 second lag time, (needing to pressurize the cylinder) but it was good to me, Im sure increasing the diameter from 1/4 poly tube to 3/8 would fix this entirely.
Notice the 2 diodes needed to make it work. Make sure the diodes are a 10 watt or so so it can handle the 3 amps the whole thing takes.
Coming Soon in an edit
How the Air cylinder attaches to brake pedal
Air input is on the left, Air Output is on the right. You can see the trailer brake magnet here to "trick" the brake controller that its hooked up.