Wiki-Electric Brakes

Electric Brakes

This article was originally published in the Ambling A-frames WIKI

by Dave Michaels


What are they, and Why are they Important?

Electric Brakes are, as the name implies, 12VDC electrically powered proportional drum brakes that are controlled from the Tow Vehicle (TV).

A-frame campers can be ordered from the Columbia Northwest (Aliner) or Chalet factories with or without electric brakes. Of course, all campers travel attached to a TV which has brakes of its own, so especially the lighter campers are often ordered without electric brakes, and the TV / camper rig depends solely on the TV brakes for stopping.

Electric brakes, the only kind of brakes available on A-frame campers (unless extensive modifications are made for different kinds of aftermarket brakes), are triggered by a Brake Controller inside the TV, which controls the timing and amount of braking required of the electric brakes, in concert with the braking that the TV is being commanded to do. In short, electric camper brakes help stop the camper when the TV brakes are stopping the TV.

Is has been argued (to death…) by some, that especially smaller campers do not need brakes, because they are so light that they will stop without problems using the TV’s brakes only. And, especially for smaller campers, this argument will often prove to be accurate. But, like accident insurance, brakes may only be really needed in an emergency, at which point they could prove to be REALLY NEEDED! A few cases-in-point:

  • Towing in rain or on icy roads – if a TV’s brakes are suddenly applied, such as during a panic stop, the non-brake camper may swing around the TV, dragging the tail of the TV with it, resulting in uncontrolled directional behavior.
  • Turning stops – Often sudden stopping while executing a tight turn can result in the non-brake camper either swinging around the TV, or weaving abruptly side-to-side, either of which will certainly compromise safety during the sudden stop.
  • Extended downhill travel with a non-brake camper can sometimes result in unstable camper weaving behind the TV, or even brake fade in the TV brakes due to overload.

Typically, if the TV is much heavier than the camper, then instances of non-brake camper instability will be reduced, because the TV is proportionally much heavier than the camper, but in turning stops, or stops on wet or icy pavement, the camper can, and has, swung around the TV, causing a jackknife condition that can result in injury or damage.

When a camper has properly adjusted brakes, TV brake actuation automatically actuates the camper’s brakes, forcing the camper to pull against the TV, thus keeping the camper in-line with, and behind, the TV during a sudden stop.

How Do Electric Brakes Work?

Camper mounted electric brakes have two major components – a set of two axle mounted Electric Brake Assemblies, and a Brake Controller, mounted in the TV. The Controller, as its name implies, controls the electric brakes based on the driver’s use of the TV’s brakes, so that the trailer brakes are applied and released in synchronization with the TV’s brakes. For more detail on brake controllers, please read the Brake Controller DIY article.

Electric Brake Assy

The two Electric Brake Assemblies are mounted one on each end of the axle. The brake assemblies have four major components, supported by a number of smaller components. The Brake Backing Plate (#1 in the upper diagram), is mounted with fasteners (#12 in the upper diagram) to each end of the axle, and supports two brake shoes (#6) each. Brake Shoes are curved steel plates with a high friction surface bonded to each. The two brake shoes are separated at the bottom with a Brake Adjuster Star Wheel (#7). A Brake Actuation Magnet (#9) is also built into the backing plate, on an arm (#2) which extends the brake shoes when the magnet is displaced.

The Hub-Drum Assembly (#10 in the lower diagram) is mounted over the brake backing plate, brake shoes, and brake actuating magnet discussed above. The hub-drum rotates on two bearings, an inner one (#2, lower diagram) and an outer one (#5, lower diagram), which are mounted on the spindle (the pointed end of the axle or axle trailing arm, shown at the left side of the lower diagram), and which support the rotating hub-drum assembly, and therefore the entire road weight of the camper, except that portion of the camper’s total weight that is supported by the TV, via the tow ball on the camper’s tongue. For more information about bearings, read the Bearings and Seals DIY article.

The hub-drum, supported by its two bearings, has the wheel and tire mounted to it, and is free to rotate around the brake assembly. Inside the hub-drum are two smooth machined surfaces. One is axial, meaning it is machined into the inside of the hub flange, parallel to the axis of rotation of the hub, and ninety degrees to the face of the hub. The other is radial, meaning it is machined into the inside of the hub face itself. As in conventional drum brakes, when the brake shoes are pressed into the axial machined surface, the friction of the brake shoes on the axial surface causes the hub-drum to decelerate, slowing the rotation of wheel and tire, and therefore the camper. Unlike conventional drum brakes, however, the brake shoes are not actuated by an external force, such as hydraulic fluid from a pressurized source. Instead, the brake shoes are propelled into contact with the hub’s axial surfaces by the rotation of the hub itself.

When the brake controller sends current to the brakes, the current energizes the brake actuation magnet, an electromagnet which generates more magnetic attraction as more current passes through it. This magnet is positioned on an arm which, when displaced, forces the drum brake shoes into the axial machined surfaces through a linkage. The face of the magnet rests against the radial machined surface inside the hub, so that, when the hub is rotating, the magnet, when energized, is attracted to, and attempts to move in the direction of, the spinning hub. The magnet mounting arm displaces when the magnet attraction to the hub increases, and forces the brake drums into the axial hub machined surface with increasing pressure, resisting and eventually stopping the hub’s rotation. This ingenious design means that the kinetic energy of the moving camper itself is harnessed to stop the camper when commanded, with no other outside energy other than electricity being applied. Note that, by design, an electric brake only applies braking force to the hub when the camper is in motion. When the camper is stopped, electric brake application results in the magnet attracting the stationary hub, so the brake actuation arm and linkage don’t move, and shoe displacement is nil. Likewise, the electric brakes will not displace the brake shoes when the camper is backing up, because the actuation magnet arm and linkage is designed to function in forward rotation only.

NOTE: This directional sensitivity is the reason why replacement electric brake assemblies are dedicated only to the left or right side of the axle, and must Never be swapped. Typically, these assemblies are clearly marked as to the side they are designed to fit. Occasionally, the wrong side is shipped to customers by mistake, so vigilance is necessary to insure that the correct assembly is installed on each side of the axle. Swapped brake assemblies WILL NOT FUNCTION!

Like any drum brake, the shoes and the axial machined surface on which the shoes rest, must be clean and free of oil or grease, or the brake shoe’s coefficient of friction will be reduced to the point where no braking occurs even when the shoes are pressed firmly into the hubs. Any grease inside the hub will therefore destroy the braking capability of the brake assembly, and will also hinder the attraction of the actuating magnet to the hub, further reducing braking effectiveness.

Electric Brakes Can be Added to a Non-Brake Camper

Since some campers are manufactured without brakes, many owners opt to install them after purchase. Most A-frames are equipped with axles that will accommodate an aftermarket brake installation. To see if your camper has a brake-ready axle, look at the axle under the camper near the hub (where the wheel is mounted). If you see a roughly 5″ square plate with four equally spaced holes drilled into its corners, welded to the axle just inboard of the wheel hub, then you’re looking at a brake mounting plate, and your axle will accommodate electric brakes.

A-frame campers come from the factory with one of two types of axles installed. The smaller one is rated at 2000# or 2200#, and typically has 13″ wheels and tires mounted. The larger of these is typically a 3500# axle with 14″ wheels and tires. Regardless of the manufacturer of these axles, after-market brakes can easily be installed if the axles have a brake mounting plate, as discussed above. For more information about axles, please read the Axles DIY article.

The smaller 2200# axles take a 7″ x 1.25″ electric brake assembly. The larger 3500# axles take a 10″ x 2.25″ electric brake assembly. The first number in these designations, 7 or 10, indicates the diameter in inches of the brake hub, onto which the brake shoes press when braking. The second number indicates the width of the brake shoes in inches. More about brake shoes and hubs will be discussed below. Both of these brake assemblies will work with either 13″ or 14″ wheels and tires.

Regardless of the manufacturer of your axle, brake assemblies from Dexter, a nationally known and stocked trailer systems parts supplier, will fit either size axle. Of course, you can purchase brakes in either of these sizes from Al-Ko for an Al-Ko axle, or from Henschen for a Henschen axle, but you’ll pay more for the same basic brake assembly, and the Dexter brake assembly will use parts that are far more readily available if you have a failure on the road, and they will be cheaper, too.

Here are the Dexter Part Numbers for the 7″ x 1.25″ and 10″ x 2.25″ brake assemblies. These parts can be used to retrofit a non-brake equipped axle, or to replace existing brake assemblies on any A-frame axle, whether torsional or straight with leaf springs.

  • 7″ x 1.25″ Electric Brake Assembly without parking brake – Dexter # K23-047-00 (Left Hand side)
  • 7″ x 1.25″ Electric Brake Assembly without parking brake – Dexter # K23-048-00 (Right Hand side)
  • 10″ x 2.25″ Electric Brake Assembly without parking brake – Dexter # K23-026-00 (Left Hand side)
  • 10″ x 2.25″ Electric Brake Assembly without parking brake – Dexter # K23-027-00 (Right Hand side)
  • 10″ x 2.25″ Electric Brake Assembly, Nev-R-Adjust, without parking brake – Dexter # K23-468-00 (Left Hand side)
  • 10″ x 2.25″ Electric Brake Assembly, Nev-R-Adjust, without parking brake – Dexter # K23-469-00 (Right Hand side)

The notation “Left Hand side” refers to the left side of the camper as viewed from the rear, i.e., the street side. The “Right Hand side” notation refers to the right side of the camper as viewed from the rear, i.e., the door side. The notation “without parking brake” is to insure that a brake assembly with parking brake option is NEVER ordered for an A-frame. Likewise, these same brake assemblies are also available with hydraulic actuation, instead of electric, but hydraulic brakes are never used in A-frame campers either, unless as the result of extensive modifications, which I’ve never seen on an A-frame…

The Nev-R-Adjust notation refers to a recent innovation that allows the brake assembly to self adjust as the camper rolls forward and brakes are applied. These new brake assemblies still have a manual adjustment like the older ones, but they also contain a self adjusting pawl that should reduce or eliminate the need for manual adjustment after the initial adjustment when they are installed.

Note that the brake assemblies listed above include the brake mounting plate (which mounts to that 5″ square plate we discussed previously), and all the components attached to the mounting plate, which we’ll discuss later on. They do NOT include the parts of the brake assembly which rotate with the wheel and tires. These parts are sold as a separate assembly called the Hub-Drum Assembly. The reason the brake and hub-drum assemblies are not bundled into a single assembly is that hub-drums are available with different bolt patterns for different wheels using the same brake assemblies. Also, brake assemblies contain wear parts (specifically the brake shoes, more of which later on) and are therefore often replaced without having to replace the hub-drum assembly.

Here are the corresponding Dexter Part Numbers for the 7″ and 10″ Hub-Drum Assemblies that fit the 7″ and 10″ Brake Assemblies listed above, and also fit the 13″ or 14″ wheels used on our A-frames, all of which have a 5 – 4.5 Bolt Pattern. For more information about wheels and bolt patterns, please read the Tires and Wheels DIY article.

  • 7″ Hub-Drum Assembly – Dexter # K08-257-91 (two required – one for each side)
  • 10″ Hub-Drum Assembly – Dexter # K08-247-94 (two required – one for each side)

Both of these hubs support the Ez-Lube hub caps with rubber insert, which facilitate easier, one point lubrication for each hub. For more information about Ez-Lube hubs, please read the “Lube Types” paragraph in the “Configuring Aftermarket Axles” portion of the Torsional Axles DIY article.

When you order a Left Hand and Right Hand Brake Assembly, and two Hub-Drum Assemblies in either 7″ or 10″ sizes as shown above, you’ll have everything you’ll need to upgrade your non-brake axle to an electric brake axle.

The next discussion will deal with how to install electric brakes on your camper.

Installing or Replacing Electric Brakes

The following information applies to installation of new Brake and Hub-Drum Assemblies onto non-brake axles, AND to replacement of worn out Brake Assemblies or Hub-Drum Assemblies on existing brake installations. We’ll talk first about how to remove the existing assemblies, then we’ll discuss installation of new assemblies. For a new installation onto a non-brake axle, you will first need to remove the non-brake hub from your axle, following the removal portion of this discussion, then reference the installation portion of this discussion to install your new brakes.

For replacement of Brake or Hub-Drum Assemblies, or removal of a non-brake Hub Assembly, the first move is to remove the old assemblies from the axle. Here is the drill:

Removing the Hub-Drum and the Brake Assembly

Follow this procedure to remove the hub-drum and brake assembly.

  • Jack the camper until the tires are off the ground. Lower the camper onto stable jack stands – don’t rely on the jack to hold the camper up while you work on it!
  • Remove the wheels on both sides. Use this opportunity to rotate the wheels side-to-side, if you care to.
  • Using a sharp flat screwdriver, hammer, and a block of wood, gently coax the hubcap (#8 in the lower diagram, above) off of the end of the hub. NOTE: The hub cap is a silver colored press-on cap, often with a black rubber plug in its center, and is NOT the black vanity cover that comes off the axle when you remove the wheel on some campers. Start by placing the screwdriver into the margin (the tiny gap) between the hubcap and the hub. Gently tap on the screwdriver until the blade is forced into the margin. Twist the screwdriver gently until the hubcap starts to come loose. Rotate the hub, and do this in several more places, steadily enlarging the margin until the hubcap falls off.
  • Locate the cotter pin (#7, lower diagram) locking the castellated nut (#6, lower diagram) inside the hub. If properly lubricated, the hub cap end of the hub assembly will be full of grease. Pull the cotter pin out of the end of the spindle and discard it. Turn the castellated nut counterclockwise until it is free of the spindle. Remove the Spindle Washer (#9, lower diagram).

NOTE: By way of explanation, Cotter Pins are small cleft pins make of soft metal, which can be easily bent after pressing into a hole, so that the pin stops a castellated nut from turning. A Castellated Nut is like a normal nut, but has lateral cuts in its top surface, resembling a castle. A cotter pin slides through one of these cuts, locking the nut in place. The Spindle is the shiny stub protruding 90 degrees from a torsional axle’s swing arm, or directly out of the end of a straight axle, onto which the brake assembly and the hub-drum assembly are mounted.

  • Carefully slide the hub assembly away from the spindle until it comes free. NOTE: If you are installing new brakes onto a non-brake axle, the removal portion of your project is now complete. Skip down to the Install portion of this discussion. If you already have brakes on your axle, and wish to replace them, let’s continue with removal.

NOTE: While the individual parts of a brake assembly, such as brake shoes or actuation magnets, can be replaced in the field, it really makes more sense to replace the entire brake assembly, so that all the parts are renewed. The cost of a complete replacement assembly is quite low, and is only marginally higher than the cost of parts, but with a completely new assembly, all parts are new, and there’s much less work involved.

  • Slide under your camper, and locate the (typically red) wires that are connected leads that go into the brake backing plate at each end of the axle. Typically the red wires are connected to the brake leads using wire nuts. Disconnect these wires from the leads going into the backing plate.
  • Next, locate and remove four mounting nuts on the inboard side of each brake mounting plate (the square plates welded to the axle body, onto which the brake backing plates are mounted).
  • Remove the brake backing plate (#1, upper diagram) and all its parts from the axle mounting plate.

Installing New Brake and Hub-Drum Assemblies

Follow this procedure to install new hub-drum and brake assemblies.

  • Locate the correct brake assembly for the side of the axle on which you’re working. THIS IS VERY IMPORTANT! Do NOT swap sides! The brakes WILL NOT FUNCTION if they’re mounted on the wrong side!
  • Slide the brake backing plate (#1, upper diagram) containing the brake assembly, onto the brake mounting plate welded to the axle. Tighten the four nuts (#13, upper diagram) behind the brake mounting plate to 45 – 70 ft. pounds of torque.
  • Connect the two leads from each brake assembly to the corresponding wires from the camper, using two wire nuts to connect them. Polarity of the wires is unimportant. Make sure the brake wires don’t rub on anything when the axle articulates under road loads.
  • Side a hub-drum assembly (#10, lower diagram) onto the spindle, so it covers the components of the brake assembly. The same hub-drum assembly fits either side of the axle. When you slide the hub on, you are also installing the bearing seal and the inner bearing, both of which are already mounted inside the inboard end of the hub-drum.
  • Slide the outer bearing (#5, lower diagram) onto the spindle, with the tapered (smaller) end of the bearing pointing into the hub-drum.
  • Slide the spindle washer (#9, lower diagram) onto the spindle so it nests next to the outer surface of the bearing.
  • Fit the castellated nut (#6, lower diagram) onto the threaded end of the hub-drum, and rotate it clockwise until it runs into the spindle washer.
  • With a wrench, carefully turn the castellated nut until it seats tightly against the outer bearing. Do NOT rotate the hub-drum while doing this!
  • Back the castellated nut off of the bearing by turning it counterclockwise until the nut turns freely by hand. Support the weight of the hub-drum with your other hand while doing this, so you get a true feel for when the bearing is hand-rotatable.
  • Rotate the castellated nut clockwise BY HAND until it runs into the bearing and stop. DO NOT FORCE THE CASTELLATED NUT ANY FURTHER!
  • Back the castellated nut off slightly by turning counterclockwise until one of the gaps in the castellated portion of the nut lines up with the cotter pin hole drilled into the threaded end of the spindle. Note that the hub-drum assembly turns easily, with a very slight axial bearing play, before continuing. If the hub-drum grinds while turning it, the castellated nut is too tight. Note that the brake shoes will scrape against the inside of the hub-drum – this is normal. Bearing grinding is not normal, and must be corrected by backing out the castellated nut, and repeating the previous five steps, including this step.
  • Fit a cotter pin (#7, lower diagram) into the spindle end, so that it retains the castellated nut, and then bend the open ends of the cotter pin apart from each other so they are flush with the sides of the castellated nut. BE SURE no part of the cotter pin protrudes sufficiently to hit the hub cap when you install it.
  • Position the hubcap (#8, lower diagram) onto the end of the hub-drum, and gently tap it into place using a hammer and a block of wood positioned against the hub cap. NEVER hit a hub cap with a hammer without wood protection! It’ll likely leak grease if you do!

Brake Maintenance

Lubricating (Greasing) the Hub-Drum Bearings

Before adjusting brakes, let’s be sure to grease the bearings in our new hub-drums. Here’s how:

  • RECOMMENDED GREASE – any Lithium grease compound with a minimum Viscosity of 80 and a Minimum Dropping Point (refers to heat resistance, it is analogous to a melting point) of 215 degrees Celsius, or 419 degrees Fahrenheit will do the job. Don’t mix grease types inside the hub – if you change grease compounds, first clean out the old grease before using the new.
  • If you have Ez-Lube hubs, remove the rubber cover on the hubcap, and locate the grease fitting (called a Zerk Fitting) protruding from the end of the spindle, inside the hubcap.
  • Fit a grease gun onto the zerk fitting, and pump grease into the hub until you see grease coming out of the outer bearing at the edges of the hub opening for the hub cap, and starting to spill into the hub cap area.
  • Remove the grease gun, and cover the hubcap with the rubber cover.
  • If you have standard hubs drums, without Ez-Lube, there will be a zerk fitting built into the hubcap. Grease injected into this fitting will eventually emerge from the backside of the spindle (inboard of the brake assembly) whereupon grease injection should be stopped.
  • If your hub-drums have neither of these styles of grease injection using a zerk fitting, then the hub has to be removed, and the bearings removed from the hub, so they can be individually packed with grease. Very few campers have this older style of hub-drum. They are identified by their hubcaps, which have no rubber cover or zerk fitting on them.

Initial Checking of Your New Brake Installation

Now that you have installed, or reinstalled, new brake and hub-drum assemblies, or if you just need to maintain your brakes after extended use, you will need to check and adjust them for maximum braking performance.

  • Before removing the jack stands from your camper, turn each wheel and note smooth operation, with some scraping sounds from the brake shoes contacting the inside of the hub-drum. Attempting to wiggle the tires perpendicular to the camper should result in very little, if any, wheel wobble.
  • Connect the TV to the camper, and apply the electric brakes manually using the TV brake controller. Both wheels should rotate only slightly before freezing, when spun by hand.
  • Lower the camper to the ground, and tow it out onto an uncrowded road.

Breaking In, or Burnishing, Your New Brake Shoes

This is necessary only if you have just installed new brake shoes. Doing this will shape the brake shoes to match your hub-drums, and will prepare the brake shoe surfaces without glazing (burning) them.

  • Accelerate to 40 mph, and apply full braking using only the manual control on your trailer brake controller. If this locks the brakes, turn down the brake voltage using the controller’s manual adjustment, however, typically, this won’t happen at 40 mph.
  • Let the trailer brakes slow the TV and trailer to 20 mph. Release the trailer brakes.
  • Tow the trailer to allow the brakes to cool.
  • Repeat the above two steps 20 times. Be sure not to overheat the brakes during this process. You will notice brake performance will increase as you continue to burnish the brake shoes using this process.

Adjusting Your Brake Controller

Once you have burnished your brake shoes, it will be necessary to adjust your brake controller until, in a full panic stop, the controller applies the brakes until they are just about to lock, but not to the point where they actually do lock up. This is called the Point of Incipient Lock.

  • Load your camper as it will be when you go camping (fully loaded).
  • Accelerate to 20 mph, and apply full manual braking using only the manual control on your trailer brake controller. If this locks the brakes, turn down the brake voltage using the controller’s manual adjustment, and repeat this step.
  • Do the last step, above, as many times as it takes to find a voltage adjustment that almost locks the brakes at 20 mph. The brakes should not lock when the camper goes over bumps in the road using this voltage adjustment.

NOTE: Different loads, tire pressures, road surfaces and conditions, and outside temperatures will all impact Incipient Lock, so it may be necessary to adjust the braking voltage per the instructions above, at various times during a camping adventure, to insure full braking capability without locking the brakes. In any event, be sure to do this adjustment any time you hear the brakes lock in normal use.

Adjusting Your Brake Shoes

When installing new brake and hub-drum assemblies, it is usually not necessary to adjust the brake shoes, unless the shoes don’t touch or scrape the inside of the hub-drum when the hub is rotated. If it is necessary to adjust the brake shoes after installation, or at any time that the brake shoes wear to the point where they need adjustment, then follow these steps.

NOTE: Most Electric Brakes used on A-frame campers are NOT self adjusting – they must be manually adjusted if they require adjustment. The exception to this are the new Nev-R-Adjust brake assemblies which provide automatic adjustment when brakes are applied while the camper is rolling forward. These new self-adjusting brakes can still be manually adjusted as described below.

  • Jack the camper until the tires are off the ground. Lower the camper onto stable jack stands – don’t rely on the jack to hold the camper up while you work on it!
  • Slide under the camper and locate and remove the rubber brake adjustment slot cover (#10 in the upper diagram at the beginning of this topic) from the Brake Adjustment Slot in the brake backing plate.
  • Slide a screwdriver or brake adjustment tool into the slot until the blade engages the brake adjustment star wheel (#7 in the upper diagram), and rotate the star wheel as you rotate the wheel and tire. If the brake shoes appear to be backing away from the inside of the hub-drum, then reverse the direction of rotation of the star wheel.
  • When the brake shoes contact the inside of the hub-drum, adjust the shoes so that the hub-drum rotates easily, but the shoes make a continuous or nearly continuous scraping sound as the hub-drum turns.
  • With the TV attached to the camper, manually apply the brakes while turning the tire and wheel in a forward direction. The tire and wheel should slam to a stop when the brakes are applied.
  • With the brakes at rest, check the brake shoe clearance by rotating the tire while listening for scraping, as in the step two above this one. Repeat the previous three steps, including this step, until satisfied that the brake shoes are properly adjusted.
  • Repeat the previous five steps on the other brake assembly.
  • Replace the rubber brake adjustment slot covers on both brake backing plates, and lower the camper to the ground.

NOTE: It may be necessary to readjust the brake controller voltage output to incipient lock after adjusting the brake shoes.


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