Answer: The job of the brake controller is to send the appropriate amount of current flow back to the brakes. You could send a full jolt of electricity back to the brakes, and they’d respond by jamming the brake pads into the drums, locking up the brakes. That’s converting kinetic energy from rolling wheels into heat way too fast—skidding the tires, making vehicle control difficult or impossible, and wearing out the brakes in a hurry.
Set properly, the brake controller also pairs up the tow vehicle and the trailer in the sense that both are braking for themselves. Too little power to the trailer brakes, and slowing or stopping the trailer falls to the tow vehicle’s brake system. Too much power to the trailer brakes, then the trailer brakes get the job of slowing or stopping the tow vehicle. If the controller is not set properly, you’ll be needlessly wearing out the brake system of one or the other, and that’s a costly and unsafe proposition for sure.
It’s important to set the brake controller settings for the job at hand. For some, this will mean doing the initial setting, and tweaking the system to get everything honed to “towing perfection.” However, if you use your tow vehicle to tow different trailers—for example, using your pickup to haul your travel trailer, and then on other occasions using it to haul a utility trailer—, the different trailer weights will require adjusting the controller more often.
Different brake controllers require different approaches to settings. It's critical you know what brake controller you have installed in your tow vehicle, and have the manufacturer’s instructions on setup. Don’t have the documents? Get the manufacturer name and model number, hit the Internet, and look for it. If your controller is old enough not to have a presence on the Web, then it’s high time you got a new brake controller.
Here's a situation with Tekonsha’s Prodigy P2 controller. A snowbird friend of was concerned that her brake controller needed adjusting—she had changed rigs since her last adjustment. We obliged, and one of us jumped in her rig with a spotter along.
Tekonsha recommends setting the power setting for its unit at “6” for a starting point. With the trailer attached and the engine running, pull the manual override lever on the controller all the way to the left—maximum brake. Holding the lever, adjust the power control knob until the digital setting shows a 6 on the display. We did that and also turned off the “boost” setting on the control.
Now locate a flat stretch of pavement, bring your speed up to about 25 miles per hour, and pull that manual override lever on full—don’t step on the tow rig’s service brakes, just pull the lever. If the trailer brakes lock up, stop, pull the override lever on full, and reduce the power level down a notch. Repeat until the brakes no longer lock up. If the trailer doesn’t respond with a lock up, up the power a notch. Repeat until you hit lock up, and then back it off slightly, and your power level is set.
In our case, we dialed all the way up to the maximum level and never got any notion at all that the trailer brakes were doing anything. An inspection revealed the trailer brakes had to be manually adjusted out—the lining was worn down enough that the brakes weren’t making contact with the drums. That can happen—the vast majority of trailer brakes, unlike those on cars and trucks, are NOT self-adjusting. They need to be adjusted “out” as lining wears down.
Adjustment done, we made another controller adjustment run. We started at level 6, and worked our way up—almost all the way to the top of the scale. We never could get the brakes to lock up, but the brakes definitely did their job. Why no lockup? Very heavy loads can be more than the system allows for a lock up. Her 40-foot (and probably overloaded) trailer just couldn’t be locked up. We recommended she run the trailer across a scale, and begin the job of tossing out excess baggage.
Regardless of brake controller make and model, some observations apply across the board. Brake temperature can make a big difference. It’s not unwise to pre-warm your brakes prior to dialing in the right setting. Your manual will tell you how to do that. Then it gets dicey—in our case, the manual advises to engage the manual brake lever on the controller while cruising down the road “at 25 miles per hour or less.” By the use of the manual engagement lever on the controller, you’ll be using the brakes on the trailer, not the tow vehicle. All very well and good, but if too much power is routed back to the trailer brakes and you’re cruising along at 25 miles per hour, you may have a BIG mess to clean up back in the trailer should the brakes lock up. At least one expert recommends checking your brakes in your driveway at say, 5 miles per hour. The objective is to see to it that the power setting of the controller will slow the rig down—NOT lock the brakes.
Here’s some other advice you may not find in the manual. Doing an initial test in a gravel lot may give a lot more feedback than on pavement—you’ll hear that gravel if you lock up, and the skid marks are a clear indicator that you’ll need to back off the gain adjustment on the controller. Once we know where things sit on gravel, then fine-tuning on pavement ensures we’ve got the controller set where it needs to be.