The cart does not have front brakes.
I suspect you meant the tire are 18", so the wheels are most likely 8". In other words, stock tires and wheels.
The first bad news is that a NCX controller has to be programmed at the factory and I don't know if they will do it or not.
You can e-mail them with the controllers serial number and ask if the regen braking can be turned on if you sent it back to them.
http://www.alltraxinc.com/contactus.html
The second bad news is, if you do have 8" rims, the aftermarket dick brakes wonk fit.
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Try the brake adjusting procedure I posted on the hard packed driveway.
Also the manuals in the link I posted have brake inspection and cleaning procedures in them.
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Your terrain sounds similar to mine. I can drive in a complete circle and be going uphill all the way.