How to Test Trailer Brakes with a Multimeter

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Trailer brakes are often needed on a trailer when a tow vehicle has a GVWR or gross vehicle weight rating of over 3,000 pounds. In some states, trailers with a GVWR as low as 1,000 pounds might be compelled to have brakes. Brakes on trailers with tandem axles may be needed on both axles if the GVWR goes beyond 5,000 pounds.

You see, trailer brakes are vital as the added weight of the trailer might be over than the tow vehicle could safely and efficiently handle. Having that added set of brakes on the trainer also enhances braking stability and lowers the risk of it jackknifing in a panic stop scenario. 

Did you know that trailer brakes are often disregarded until a problem arises? That’s why it is essential to check the brake often and make repairs if necessary.

Take note that trailer brakes are not much different than light truck brakes and passenger car brakes. They often need the same type of repairs and maintenance. Corrosion is the major issue with trailers, particularly boat trailers.

Brakes on these trailers are frequently submerged when loading and unloading the boat. That makes them prone to sticking and rust. Saltwater is really tough on the brakes. Often, the brakes should be replaced or rebuilt after three or four seasons of boating. The wheel bearings are susceptible as well to corrosion and water contamination and might fail if they’re not properly cleaned, adjusted, or repacked with grease regularly. 

What Are the Different Types of Trailer Brakes & How Do They Work? 

Trailer brakes come in two major types: surge and electric. 

  • Electric trailer brakes

These brakes are triggered by an electrical connection to the brake pedal or modifiable dash-installed inertia switch in the trailer or two-vehicle. Whenever the brakes are applied, an electric current proportional to the rate of deceleration fuels a magnet inside every brake. 

That magnet triggers an activating lever to apply the brakes. The current to the magnet is cut off, and the brakes are released when the driver takes his foot off the brake pedal. The same situation applies when the vehicle begins to move again. The controller is adjustable to compensate for different trailer loads. 

  • Surge trailer brakes

On the other hand, braking is automatic in surge brakes and needs no electrical connection between the vehicle and the tow vehicle, except for the lights. The surge coupler is installed on the trailer’s tongue. 

Inside is a connection attached to a hydraulic master cylinder. The trailer’s forward momentum drives on the surge coupler whenever the tow vehicle uses its brakes. That causes it to move rearward and apply pressure over the master cylinder piston rod. 

Surge brakes are typically utilized on boat trailers, as the electrical brakes don’t hold up very well in wet conditions. They’re also utilized on most rental trailers, as they remove the necessity for any electrical hookups other than the trailer light. 

However, in some regions, these brakes aren’t considered enough for commercial purposes or heavier trailers. Electric brakes are still needed, meaning the tow vehicle should be geared with some controller to run the trailer brakes. 

You may also find another type of trailer brake, which is the air braking system. It’s very much identical to the drum brakes in a vehicle and employs brake shoes on every wheel to slow down and stop them. 

Common Symptoms of a Bad Trailer Brake

Whether you are planning a trip to the wilderness or want to ensure your trailer is working properly, you need to ensure the trailer’s braking system is in its best condition. That’s why you need to familiarize yourself with some of the issues with a trailer brake. Some of them include:

  • The trailer pulls to one side when braking

Does your RV pull to one side when you apply force on trailer brakes? It indicates the braking application is not balanced. 

  • Weak forward electric brakes

Another issue is feeble forward braking. That’s especially the case when you have electric brakes installed on your trailer’s four wheels. In an ideal situation, the round section of the brake’s actuating arm must point forward for the trailer brakes to function as intended. 

  • Trailer brake locks near the end of the stop

Do you also notice your brake’s lock before the towing vehicle comes to a halt? That issue roots in the braking control unit’s setting. It’s highly likely the drag on the brakes is set too high, which causes wear and tear on the brake shoes. 

How to Test Your Trail Brake? 

A worn-out or faulty trailer brake could affect the trailer’s ability to stop. Some trailer brake magnet problems will be obvious by just staring at it, but some are electrical issues that could impact performance.

For visual inspection:

  • Do you see any coil on the center of the trailer brake magnet? It means it’s worn out and must be changed.
  • Take a straight edge tool and lay it across the magnet’s top. The edge must be paralleled to the straight edge all the way across. Any changes or pitting in the magnet’s surface suggest abnormal wear, and it should be replaced. 
  • Check the magnet for any oil or grease residue. 

A digital multimeter that reads ohms and amps will be required to test your trailer brake. To test with a multimeter, kindly follow the following steps:

  1. Connect the multimeter inline along with the blue wire going to the back of the brake controller. Alternatively, you can also use the diagnostic readings of the brake controller. 
  1. Is the amperage higher than the indicated amount? Then it would help if you replaced the trailer brake magnet. If the reading is less than the indicated amount, it means the leads are bad, or the magnet must be replaced right away. 

Final Thoughts

To sum up, similar to brakes on any tow vehicle, trailer brakes require regular service and maintenance. Remember that the required service frequency depends on how heavy the tow loads are and how often you tow. 

Simply put, the more you tow, the more often you ought to be checking your brakes.

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