Trailer Brakes

Trailers over a certain size/weight must have brakes.  Virtually all travel trailers are heavy enough that they are required to have brakes.  Some small utility trailers and motorcycle trailers don't have or need them legally, but it is always a good idea to have them.   Tent trailers usually need brakes but a few, ultra-light weight trailers might be exempt in some jurisdictions.  Tow dollies may or may not also be equipped with brakes.  Obviously the weight of any car is enough that you should have brakes on the dolly.  There are basically two kinds of trailer brakes:  electric brakes and surge brakes.

Electric trailer brakes are controlled by a brake controller in the tow vehicle.  The controller is connected to the brake switch so it is activated when the vehicle brakes are applied.  The controller contains a device that measures momentum.  The harder and faster the vehicle decelerates when the brakes are applied, the stronger the application of the trailer brakes.  Controllers typically have adjustments to allow the driver to increase or decrease the sensitivity of the controller to tune the trailer braking.  They also have a control to manually apply the trailer brakes.  The brakes on the trailer are activated by a magnet controlled by the amount of power transmitted from the controller.  The magnet grips the inside face of the brake drum and an attached lever pushes the shoes out against the drum to slow or stop the trailer.  Most larger trailers have electric brakes.  Some advantages to electric trailer brakes is that the sensitivity can be tuned by the driver so the trailer brakes just right, not too much and not too little and the driver can apply the trailer brakes via a button on the controller. 

Surge brakes are self contained on the trailer.   Surge brakes are hydraulic brakes.  The master cylinder is included in the surge brake activator on the trailer tongue.  The activator is designed to apply hydraulic pressure to the braking system when it senses the tow vehicle is slowing down.  What happens is there is some flexibility in the way the activator is mounted on the tongue so that when the vehicle slows down and the trailer pushes forward against the hitch, pressure is applied through the master cylinder to the brakes to slow the trailer.  The main advantage to surge brakes is that they don't need a controller in the tow vehicle.  The main disadvantages are that the driver cannot manually apply the trailer brakes and the driver can't control the sensitivity.

I have used trailers with both types of brakes and quite honestly, have not found any significant differences in normal use.  Surge brakes are pretty much automatic and don't require any tuning by the driver.  On rare occasions I have manually applied electric trailer brakes but that was mostly for testing rather than any normal use.

Trailer brakes have an emergency disconnect that applies the brakes automatically if the trailer gets disconnected from the tow vehicle.   Normally, electric brake systems use the trailer battery to power the brakes if the disconnect switch is activated.  This might work with power supplied via the trailer connector, but will be useless once the connector pulls apart.  The disconnect typically consists of a pin connected to the tow vehicle so that it is pulled out of the switch if the tow vehicle is separated from the trailer.  The pin normally holds the switch open so it closes when the pin is removed, activating the trailer brakes.  Since it is basically an on or off situation, it is likely to lock up the brakes when activated.  On surge brakes, a cable attached to the vehicle typically pulls on a lever on the activator on the trailer tongue if the two become separated and the lever applies the brakes.  Emergency braking helps to  control the trailer if it gets disconnected from the vehicle.  Of course the first line of defense are the safety chains that should keep the two fairly close together and keep the trailer from wandering off by itself.  Long safety chains may allow the emergency brake function to be activated.

Properly adjusted trailer brake systems will apply braking proportional to the tow vehicle braking so both units slow down at the same rate.

If trailer brakes are too tight or too sensitive, the tow vehicle driver should feel the trailer holding the vehicle back, especially when the brakes are applied.  If it holds it back when the brakes have not been applied the trailer brakes are definitely too tight.  If trailer brakes heat up abnormally (hubs and tires get hotter than on the vehicle), the brakes are too tight and need to be backed off to avoid damage to the brakes and tires on the trailer and prevent extra load on the tow vehicle.

If trailer brakes are too loose or not sensitive enough, the vehicle driver should feel the trailer continue to push the vehicle when the brakes are applied and the trailer may kind of "fish tail"or wander when the brakes are applied.

Ideally, the drive won't feel the trailer either holding him back (brakes too tight) or pushing him during slowing and stopping maneuvers (brakes too loose).

Sometimes you can more easily see how the trailer brakes are behaving if you are driving on gravel, sand or dirt so you can see skids marks when the trailer brakes are engaged.  Testing trailer brakes on pavement means you will mostly rely on affect you can feel from the trailer on the tow vehicle when the brakes are applied.  Otherwise you have to apply them harshly enough to lock up the wheels so the tires drag and leave marks on the pavement.  Such violent maneuvers are generally not good for either the trailer or the tow vehicle.

Trailer brakes are adjusted about the same way drum brakes are adjusted on any vehicle.  There is a star wheel between the bottom ends of the brake shoes which is turned to push the shoes out against the drum.  Once the shoes are pushed out enough to keep the wheel from being turned, the star wheel is backed off just enough to let the wheel turn freely.  In my experience I can usually still hear the brake shoes lightly brushing the drum.  If the brakes are adjusted too tight they will drag and overheat.  This diminishes brake performance and life, creates extra tire wear, and can get hot enough to cause a fire.  If the brakes are adjusted too loose, they won't work effectively to slow or stop the trailer when needed.  If you aren't sure you can adjust the brakes correctly, have it done by a mechanic who knows what he is doing.  It may take several trips to the shop to get the brakes adjusted to your satisfaction but a good mechanic can adjust them to where HE thinks they should be and that will be an excellent starting point.

Controller sensitivity on electric brakes is adjusted by a switch on the controller.  It may be a rotating knob or a sliding switch.  Increasing sensitivity makes the trailer brakes come on faster and stronger; decreasing sensitivity makes them respond slower and weaker.  If the trailer seems to be tugging on the tow vehicle when you apply the brakes, the controller is too sensitive.  If the trailer doesn't seem to slow down when you apply the brakes or you can feel it pushing on the tow vehicle, is isn't sensitive enough.  Adjusting sensitivity is largely a trial and error situation.  Ideally you want the trailer braking to match the tow vehicle braking so the two slow down and stop together.

Trailer brakes are inspected by removing the drum and examining and/or measuring the amount of lining on the shoes.  Linings that are thin, cracked, or badly glazed should be replaced.  Grooved drums or drums that show signs of over heating (usually discoloration) should be turned or replaced.  To remove the drum you will have to remove the axle nut and outside wheel bearing.  The axle nut is a castle nut that is prevented from spinning loose by a cotter pin through the notches in the outside of the nut and the axle.  Always discard the used cotter pin and replace it with a new one.  While you have the drum off, inspect the wheel bearings.   If they show signs of rust or wear, replace them.  Clean and repack the wheel bearings before reinstalling the drum.  The outer bearing can be repacked by placing a glob of grease in one hand, then holding the bearing in the other hand and pressing the outer (larger end) edge of the bearing into the grease repeatedly until the grease squished out the small end of the bearing between the rollers.  Work grease all the way around the entire circumference of the bearing.  Repacking the inner bearing can be done in the same way if you can safely remove it.  The inner bearing is held in place by a grease seal that will probably have to be replaced it you remove it to extract the bearing.  You can apply some extra grease to the inner bearing with your fingers, but you won't be able to properly pack grease into the bearing without removing it.  Be sure to force grease into the bearing and not just smear it on the outside.  The axle nut must be properly tightened when reinstalling the drum.  Your owners manual may give you instructions or torque specifications which you should follow.  If you don't have a manual or specifications, snug the nut up until the bearing retainer is tight against the bearing, making sure it doesn't cause the bearing to bind when the wheel is spun.  Then back it off about one or two gaps in the castle nut to install the cotter pin.  If the axle nut is too loose, the wheel will wobble, most likely destroying the bearings, the hub, and the drum.  If it too tight, the bearings will be over stressed and will run hot, thinning out and losing the grease and burning up.  Here again, if you aren't comfortable with your ability to make the right adjustment, have it done by a qualified mechanic.  Some trailers may have specified torque readings for the hub nuts.  Lacking torque specs I usually snug up the nuts, then back them off about 1 notch on the castle nut before installing the cotter pin.

Any fairly good do it yourself back yard mechanic should be able to service trailer brakes.  It is pretty much the same as servicing drum brakes on a car.  There are some special brake tools that make any brake job much easier but it is possible to do it with ordinary hand tools.  In particular, brake pliers are designed to reattach brake springs and while it is possible to remove the clips and springs holding the shoes onto the backing plate using pliers, it is much easier with a tool specially designed for the task.  It has a screwdriver type handle and a dime-sized shallow cone in place of the blade.  The cone fits over the clips on the retaining springs, allowing you to compress the springs and then remove the clip with a turn of the handle.  Another good tool is brake adjusting tool.  I've seen brakes adjusted using a flat screwdriver, but the size and angles of  a brake adjusting tool make it much easier and faster.  Remember, almost any task can almost be fun with the right tools and even the simplest tasks can be a pain in various body parts with the wrong tools.  You usually have a choice of several grades of brake shoes.  Price usually depends on the type of friction material used.  More expensive materials are usually more effective and more durable.  However, if your budget is tight, using standard brake shoes should that match original specifications should be adequate unless you are frequently pushing the maximum load on your trailer or towing it on a lot of mountainous roads.

Stop right!