Pennsylvania Learn to Control Your RV Trailer Brakes

New technology improves safety and reliability for braking when towing…

Electric-brake systems have been employed for several decades on most trailers that have any significant weight. Each trailer with electric brakes, in turn, also requires that the tow vehicle be fitted with a brake controller. For a number of years, brake-controller choices have been extensive — all aftermarket and all electronic — but Ford changed the game in 2005 with the first trailer-brake-control system included as an integral part of the tow vehicle’s design. The trailer-brake controller is part of Ford’s Tow-Command System. Today, GM also offers a built-in control on select vehicles. Until the advent of anti-lock brake systems (ABS), most brake controllers were tapped directly into the hydraulic lines of the tow vehicle’s on-board hydraulic-braking system. They were often described as hydraulic/electric brake controllers, as they converted hydraulic pressure in the tow vehicle’s brake system to an electric signal used to activate the trailer’s brakes directly proportional to hydraulic pressure in the vehicle’s braking system.

A significant factor in elimination of this system was the advent of ABS because vehicle manufacturers’ cautioned against tapping into the hydraulic system. The controllers displaced a small amount of brake fluid, and with ABS systems, brake-cylinder volume was more limited, so manufacturers warned not to add controllers that displaced more than 0.02 cubic inches. The tap-in could not occur downstream of the ABS mechanism, so the pressure was on to devise alternate systems. Electronics were the answer, and many different types of aftermarket brake controllers were developed — none tied in with the tow vehicle’s hydraulic system, however. Even in the old days of hydraulic/electric controllers, all were sold in the aftermarket, until Ford became the first to offer a trailer-brake activation system installed at the factory.

Timer-Based vs. Proportional

1452115_P3-Brake-Control.jpgA timer-based brake controller has a timer that generates an output signal for your RV’s brakes that increases with the amount of time you keep your foot on the brake pedal. It doesn’t know whether you’re braking gently on a gradual downhill grade, or if you’re in a panic stop. The rate of increase in output (the slope of the voltage ramp) has no bearing on pedal effort, but can usually be adjusted for braking aggressiveness.

An inertia-based proportional controller generates an output that is, as the name suggests, directly proportional to your braking needs. Most proportional brake controllers measure the tow vehicle’s rate of deceleration by means of a pendulum. The quicker you slow, the further the pendulum is displaced, via inertia, from its at-rest position. This creates an electric signal to your trailer’s brakes that is proportional to your deceleration rate. Tekonsha and its sister companies use a series of LEDs and photoelectric detectors in their proportional controllers to determine the position of the displaced pendulum, and therefore determine the deceleration rate. Hayes-Lemmerz uses the Hall effect, a well-known physics principle involving moving magnets, to determine the pendulum’s position. All pendulum controllers are subject to some inaccuracies, as the pendulum can tilt slightly forward or backward on steep grades. Most such controllers employ a damping device to stabilize the sensor against vibrations, and the damper helps reduce the effect of the fore-or-aft-tilt problem. The pendulum’s position is adjusted through the level-control knob. This allows the pendulum to be oriented to a true vertical resting position to compensate for the angle of the brake-controller body (the “leveling” referred to in some timer-based-controller advertising). The level adjustment also allows the driver to pitch the pendulum slightly forward or aft of its normal resting position to set up the trailer so its braking is aggressive or delayed.

Most drivers prefer some braking effect from the trailer’s brakes on the initial touch of the brake pedal, and adjust the brake controller accordingly to provide this so-called threshold voltage. This adjustment produces some output (typically 2 volts), without the initial time period having passed or deceleration having occurred in the two electric brake-controller types. This time period, or deceleration event, is normally needed to activate the timer-based controller or the proportional pendulum-based controller, respectively.


Which is Which?
With dozens of different models of brake controllers on the market, many RVers may find the selection of the right controller difficult without some form of guidance. While budgetary considerations may force a user into one category of controller, this is a critical system where pinching pennies may not be advisable. When faced with the need for a panic stop, most drivers want a controller that will respond in proportion to their braking needs at that moment. Keep in mind that a timer-based controller can’t respond in this manner, as its output is fixed for a certain timed duration.

I hope this helps you understand what your RV brakes are doing while you are on the road.  If you have any questions about your brake controller or would like to upgrade to a newer one, give your central Pennsylvania RV Parts and Service Center a call at 800-722-1236.  Our team will gladly help you.

Safe Travel and Happy RVing!


Portions of this blog are a re-posting of an article by By Fred Pausch from Trailer Life magazine.
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