Whether you use a trailer for personal, business, or even commercial use, it is critical for your safety and the safety of others that you have a reliable braking system not only on your tow vehicle but your trailer as well. For reasons we will be examining later on, electric trailer brakes are becoming increasingly popular for their advanced features. But what if your trailer has hydraulic brakes?
In this article, we examine how to convert hydraulic brakes to electric. A step-by-step guide to
- removing the wheels, hubs, and drums
- dis-assembling the old brake components and removing the hydraulic backing plates and lines
- installing new electric backing plates, and
- wiring the new electric brakes.
So if you already own a trailer that has hydraulic brakes fear not, it is not only possible to have them converted to electric brakes, but if you are somewhat mechanically inclined, you can even perform the conversion yourself. But first, having a basic understanding of the different types of trailer brakes and how they work will enable you to make an informed decision as to the best braking system for you.
Trailer Brake Basics
As far as the actual braking itself, trailer brakes work much the same way as brakes for vehicles. All brakes work by converting kinetic energy, which in the case of a vehicle is the energy of its motion, into friction, which stops the vehicle’s motion. Friction is the resistance that one surface encounters while moving or rubbing against another surface (usually in the opposite direction).
What supplies the necessary friction in the case of brakes is the softer friction material rubbing against the braking surface. Drum brakes create friction by forcing brake shoes up against the inner wall lining of drums attached to the wheel hubs. Disc brakes force brake pads that are mounted on calipers against large discs that are attached to the wheel hubs, essentially squeezing them.
In the case of trailers, drum brakes are mounted on each wheel so that the trailer has its own braking system instead of relying solely on the towing vehicle’s braking system for both to come to a stop. It is the manner in which the brakes are engaged that differentiate hydraulic trailer brakes from electric trailer brakes.
How do Hydraulic Trailer Brakes Work?
Just as the towing vehicle’s braking system relies upon a master cylinder that generates sufficient hydraulic pressure, so too does a trailer have its own master cylinder to create hydraulic pressure within the trailer’s braking system.
The master cylinder of the trailer is incorporated into the hitch assembly that attaches the trailer to the towing vehicle (often times it resembles a box). It is helpful to think of the trailer hitch as a two-piece mechanism in which the rear piece, which is attached to the trailer, can slide into the forward piece, which is attached to the tow vehicle. Within the two pieces is a rod that activates the master cylinder.
When the brakes are applied in the tow vehicle, the forward momentum of the trailer will cause the rear piece of the hitch assembly to slide forward into the forward piece. The compressing action causes the inner rod to push into the master cylinder, which in turn generates hydraulic pressure that engages the brakes in the trailer. When the towing vehicle accelerates, the two hitch pieces pull apart, and the trailer brakes disengage.
Drawbacks of Hydraulic Trailer Brakes
There are several distinct disadvantages to hydraulic braking systems on trailers. From a safety standpoint, because of the way they work, there is a lag time involved with hydraulic trailer brakes. It is only once the towing vehicle begins to slow down, and the rear piece of the hitch assembly slides into the forward piece that the trailer’s master cylinder engages, and the trailer’s brakes are applied.
Another disadvantage is when the towing vehicle is shifted into reverse, for instance, when backing out of a parking space or similar type maneuver. When the tow vehicle moves in reverse, the forward hitch assembly piece is “backed” into the rear hitch piece triggering the master cylinder and engaging the trailer’s brakes the same way that they engage when the tow vehicle brakes while moving forward.
To combat this unintended braking, most hydraulic system hitches have a pin that can be inserted when the tow vehicle moves in reverse to prevent the two hitch pieces from moving into each other; this pin must be removed before the tow vehicle resumes forward motion to enable the brakes once again.
NOTE: On newer hydraulic hitches, there is a wire that attaches to the tow vehicle’s reverse light circuit. When the tow vehicle is put into reverse, the reverse light circuit activates and engages a solenoid that prevents hydraulic fluid from moving in the trailer’s brake lines and applying the brakes. When the tow vehicle is shifted into a forward gear, this solenoid deactivates.
How do Electric Trailer Brakes Work?
Unlike hydraulic trailer brakes that rely upon compression of a master cylinder to generate hydraulic pressure to engage the brakes, electric brakes supply electrical current to electromagnets inside each drum, which engage the brake shoes against the drum lining when the tow vehicle’s brakes are applied.
The electromagnet is nestled among the brake shoes, return springs, and other braking components on the drum brake backing plate. As the wheel moves, the inner drum surface (not the drum lining which the brake shoes rub against during braking) rotates just apart from the electromagnet.
When the tow vehicle’s driver applies the brakes, an electrical current is sent to the electromagnet which, when energized, becomes immediately attracted to the adjacent inner drum surface. As the electromagnet grabs hold of this surface, it engages a swing arm, which then mechanically forces the brake shoes outward against the drum lining to slow the trailer’s motion.
Brake controller
While the electromagnet does its work inside the drum, a brake controller inside the tow vehicle’s cabin regulates the electrical signal and current that engage the trailer braking system. Newer vehicles such as heavy-duty pick-up trucks and large SUVs, which commonly tow trailers, can be fitted with an integrated brake controller by the dealer. There is also a growing availability of aftermarket controllers.
Today’s brake controllers can perform complex functions, including recognition of the amount of force being applied to the tow vehicle’s brake pedal (e.g., hard braking vs. easy braking) and regulating power to the drums accordingly. The more power that the electromagnet receives, the greater the force with which the brake shoes are pushed against drum lining and the harder the stop.
It is the ability to adapt trailer braking performance to different trailer sizes and weights that is the true advantage to electric trailer brakes, and this is accomplished through the brake controller. There are two main variables that can be programmed through the brake controller, the (1) gain and the (2) delay.
- GAIN – the basic purpose of the gain setting is to maximize the braking force for the amount of weight represented by the trailer without locking up the wheels (skidding). This creates the greatest braking efficiency as far as stopping power, which is essential for safe towing. It is also crucial for breakaway braking, which we will be discussing later in this article.
Brake controllers have a hand-operated manual override that applies the brakes through the brake controller without the tow vehicle’s brakes being applied. To start, set the gain to about 50%, accelerate the tow vehicle to around 15 to 20 miles per hour and apply the trailer brakes only using the manual override.
If the trailer wheels lock up or skid, the gain is set too high. If the trailer (and tow vehicle) do not slow down or stop within a safe, reasonable distance, then the gain is set too low. This process should be repeated (on a long, straight, open area such as an empty parking lot) as needed to achieve the desired result.
NOTE: The gain must be re-programmed anytime the trailer weight changes significantly or when a different trailer is attached to the tow vehicle.
- DELAY – Certain electric brake controllers can also regulate the amount of time delay between the tow vehicle driver’s foot hitting the brake pedal and the trailer’s brakes engaging. Under normal driving circumstances, simultaneous braking of the tow vehicle and the trailer is ideal for preventing one from working harder than the other.
There may be instances where a slight, momentary delay between the tow vehicle braking and then the trailer’s brakes engaging is preferred, such as to control trailer sway and in certain traffic conditions.
Can You Convert Hydraulic Brakes to Electric?
Although the process of converting hydraulic brakes to electric involves many steps and requires basic familiarity with power and hand tools, electrical wiring, and good old fashioned elbow grease, it can be performed by a non-professional. Basically, the conversion entails replacing the hydraulic backing plates with electric versions and removing all hydraulic lines and replacing them with electrical wiring.
(Ideally, the trailer should be raised on a hydraulic lift to provide easy access to the underside of the trailer as the hydraulic lines will need to be removed and the new electrical wiring installed in their place. Otherwise, it will be necessary to crawl underneath or work while lying flat on your back.)
Here are the steps:
STEP ONE: Remove all four wheels from the trailer to expose the hubs/drums.
STEP TWO: On each hub/drum is a dust cap that shields the inner nut from grease and dirt. The dust cap needs to be removed by tapping it from different sides with a wooden or rubber mallet. Repeat for the other three hubs/drums.
STEP THREE: With all the dust caps removed, loosen the large nuts that secure the hubs/drums and remove all four hubs/drums exposing the hydraulic brake backing plates.
STEP FOUR: Locate the hydraulic lines and loosen all line connections in order to drain brake fluid. The hydraulic lines will also need to be disconnected from their fittings behind each of the four backing plates. Dislodge the hydraulic lines from their housings and clips and remove completely from the trailer.
STEP FIVE: Each backing plate will be secured to the axle flange by four or five nuts. Loosen the nuts and remove each backing plate from their flanges.
STEP SIX: Removing all backing plates should expose bare axles. With a clean, dry cloth, wipe each axle end to remove dirt, grease, and grime.
STEP SEVEN: Lay all four electric backing plates in front of you. Each backing plate should have a label indicating the left or right side of the trailer as well as which side of the backing plate should face forward.
In addition, each backing plate should be oriented properly when positioned onto the axle as misplacement will result in poor braking and damage to braking components on the backing plate.
The side of the backing plate with the electromagnet should be oriented down toward the ground (electromagnet at roughly six o’clock position).
STEP EIGHT: Prior to attaching the electric backing plate to the axle flange, ensure that the two lead wires in the back of the plate are properly secured so as not to get pinched between the back of the plate and the axle flange once the nuts are fastened.
Attach the backing plate to the flange and firmly tighten all nuts. It may be necessary to use lock washers or thread sealant to prevent slippage or loosening.
One of the lead wires must be grounded to the chassis of the trailer. The simplest way is to attach a ring connector and screw into the chassis allowing for sufficient slack to accommodate the rigors of driving. The other wire will be attached to the main electrical wire for the braking system.
STEP NINE: Repeat the Step Eight for the other three backing plates and grounding wires.
STEP TEN: Examine the insides of the hubs/drums. If the inner surface (not the lining surface contacting the brake shoes) is smooth, then these hubs/drums can be re-used with the electric backing plates as the electromagnet needs a smooth metallic surface to grab hold of when activated by electrical current.
Re-position each hub/drum and re-tighten the large nut. Test each hub for free movement by rotating by hand and loosen the nut slightly if necessary.
The dust cap must be carefully positioned into place. Do not hammer the cap directly to lock into place; place a large block of wood over the cap and hammer the wood instead. Re-attach all wheels.
STEP ELEVEN: This next step will adjust the tension of the brakes. Behind each backing plate are small plastic covers which, when removed, provide access to the brake tensioner. A tensioning tool will be needed. Tighten the tensioner until the wheel cannot be turned by hand. Then loosen approximately 8-10 notches.
Repeat for all three remaining wheels.
STEP TWELVE: Run a 10-gauge wire from the front of the trailer to the rear, using the same clips and openings that the hydraulic lines ran through. Blue is a common wire color for electric brake wiring on trailers.
Using a crimp butt connector, connect this main blue wire to one of the rear brake lead wires (the other was grounded to the chassis in Step Eight).
Each of the three remaining brakes will be connected in a similar fashion to the main blue wire by using jumper wires and quick splice connectors (to avoid the necessity of soldering). It is advisable to then wrap each crimp connector and splice connector with heavy duty electrical tape to protect against moisture.
All the brakes have now been installed, and the wiring to each brake completed. The remaining steps will be connecting the trailer wiring to the electrical brake controls to ensure that running lights, brake lights, and turn signal lights are operable. Electrical trailer brake systems typically use a 5 or 7-pole connector, and wiring should be performed to each manufacturer’s specifications as wire colors may differ.
Important Safety Feature for All Trailers – Breakaway Braking
A crucial safety feature on both hydraulic and electric trailer braking systems is known as breakaway braking. In the event that the hitch fails and the trailer separates from the tow vehicle, the breakaway braking feature enables the trailer’s brakes to engage automatically upon separation and independently from the tow vehicle’s braking controls.
In a hydraulic brake system, a lever connected to the master cylinder assembly is attached to a cord which is also attached to the tow vehicle. If the trailer separates from the tow vehicle, this cord will pull on the lever, which will activate the master cylinder and immediately engage the brakes.
In an electric system, a battery independent from the tow vehicle will provide electrical current to the brakes when triggered by separation of the trailer. Although it may seem a daunting task or costly expenditure, converting hydraulic trailer brakes to electric is an investment worth seriously considering, especially where driving safety is concerned. Not only are electric brakes more adaptable to the particular trailer you are towing but also varying tow weights and driving conditions.