Tractors have them, dune buggies have them, and now more and more rockcrawlers and trail rigs have them. They are known as cutting brakes. Cutting brakes are a system of levers, switches, or pedals that allow you to lock up individual brakes in order to stop one wheel and then use the other wheels to drive the vehicle, thus pivoting around that locked wheel. The result is a tremendously tight turning radius, and they can be implemented in a variety of ways.
The best recipe for using cutting brakes requires selectable lockers and a transfer case that can engage the front or rear axle individually, but there are many other less expensive, yet just as rewarding setups. One thing to be extremely careful with is using cutting brakes at high speeds and on the street, as it can have deadly consequences. Read on about how some old-fashioned farm tech can make your crawler corner.
On many tractors the brake is divided into two pedals, one for the left rear wheel and one for the right rear wheel. If you need to stop, you step on both pedals at once. But if you want to turn really sharp, you step on one pedal and turn the steering wheel, and the tractor will spin around the wheel that is locked up. We found many different models of CNC cutting brakes at Poly Performance. This is the style found on most competition rock buggies and many dune buggies. They work by plumbing your brake lines into each lever's mini-master cylinder before it runs to each wheel brake or axle. Then when you want to lock it up, simply pull the lever and that wheel/slave cylinder locks the binders up. Then hold the lever, make your maneuver, let the lever go, and keep driving.
When you want to turn sharply in your 4x4, simply engage a cutting brake for one of the rear wheels and this will let the front axle pull you around the turn. This works very well in a vehicle that either has a selectable rear locker and/or a transfer case that allows you to engage the front axle only. If you have a full-time locker in the rear like a Detroit, you need to engage the front axle only, otherwise the rear tires will drive through the cutting brakes. If you have a rear selectable locker like an ARB, Ox, or E-locker that gives you an open differential when unlocked, you can unlock the rear locker but still engage four-wheel drive when you use one rear cutting brake. This will send the power to the three unlocked wheels and you will pivot around the locked one. | 
In some situations you can achieve an even tighter turning radius if you can unlock the rear locker, put your transfer case in front-wheel-drive only, and lock the cutting brake on the rear tire opposite of the direction you want to turn. This will allow the inside rear tire to actually turn backwards as you pivot around the outside rear tire while your front tires pull you around. However, this maneuver often requires that you be pointed up a hill, and you must let the front tires spin and actually lose traction so you can slide back around the locked tire. | 
Another option is to use cutting brakes as a cheap traction tool. Say you have a cutting brake at each rear wheel, but you do not have a locking differential. You could be driving up a hill and one rear and one front wheel start to spin until you stop moving forward. By applying the cutting brake to the spinning wheel, the open differential will send power to the other wheel, and if it has traction it will begin pulling you up the hill. This is sort of a poor man's traction control. |
Of course placement of the lever needs to be easy for the driver to reach. Many buggies have them mounted between the seats, between the driver's legs, or between the driver seat and the sidebars. |  | 
Another cool trick we've seen is using a line lock (also known as a roll control or roll stop) such as this one. It can be plumbed right on the axle and is activated either electronically or by switching a valve. Simply step on the brake pedal to apply the brakes, flip a switch that activates a solenoid, or close the line-lock valve-depending on the design you're using-and it holds the pressure in the wheel cylinder to lock the wheel. |
We have also seen trail-rig builders taking tricks from the tractors by putting dual brake pedals in their rigs. This allows them to lock either the front axle or the rear axle. Locking both brakes on the axle still helps in doing tight turns with the front axle driving only (commonly referred to as a "front dig"), but not as well as locking each individual corner. | 
In the competition rockcrawler scene, Becca and Dustin Webster rely on cutting brakes for many different technical maneuvers in the rocks. They have even found that by using cutting brakes in their Red Bull-sponsored buggy they no longer need to use sway bars to control body roll. They only run selectable ARB Air Lockers and they claim that when they apply a rear cutting brake it forces the air shock at that corner to shorten while the opposite air shock lengthens on the unstopped wheel. However, on the front it works just the opposite with the braked-wheel corner shock lengthening and the unstopped-wheel corner shock shortening. This seems very complicated, but in competition these little tricks seem to help them. | 
Finally we want to see some low-buck wheelers using emergency-brake handles as your cutting brakes. If you have drum brakes in the back of your 4x4, then there is probably a cable that engages your parking brake. Simply remove the factory e-brake pedal if it has one and replace it with two brake handles from a car. We found them in many import cars at the junkyard for less than $15 each. Run a cable to each rear drum, and now you have big drum cutting brakes. This would be a great cheap way to get cutting brake for using as a traction control in your budget wheeler. |