Your trailer's brakes are one of the most important parts of the equipment overall; without properly functioning brakes, you may see that your boat or other item you're towing winds up slamming into your car or truck every time you need to step on your own brakes. Unfortunately, some vehicle owners don't realize how trailer brakes work and how they need to be maintained and repaired. Since a trailer's brakes are vital for its overall safety and function, as well as for your safety, note a few tips for troubleshooting brake problems with your trailer.
Brakes don't release
If the brakes on the trailer seem to stay applied after you release your vehicle's brakes and you feel a resultant drag from your trailer, you need to locate the master cylinder of the trailer. Then, look for the orifice that releases brake fluid from this cylinder to the brake's themselves. If this orifice is clogged, the brakes may be filled with fluid even after you release your brake pedal as it doesn't return to the cylinder. In turn, the brakes stay engaged. Cleaning the orifice can fix this, or you may need to change the master cylinder altogether if the orifice is damaged beyond repair.
There is also what is called a steel push rod attached to the master cylinder. The master cylinder will move and contract to deliver brake fluid as needed; if this rod is bent or broken, the master cylinder won't return to its idle state and brake fluid will stay in the brake pads, keeping them engaged. This rod should be located under a piston attached to the master cylinder and if it's bent, it needs replacing.
Some wheels stop, but not all
If it seems that some wheels on your trailer brake as they should but you know that some keep rotating after you apply the brake pedal, first check the brake pads to the wheel that doesn't stop in particular. If the pad is worn, change both sides as they usually wear out at the same time; even if one pad on one side seems in good condition now, it will probably wear out soon enough.
If the pads are still thick and not worn, run your hand along the brake line from the master cylinder to the wheel that doesn't stop. If it's kinked or damaged, that wheel is not getting brake fluid. You can replace that line and the brakes to all wheels should then work properly.
An auto parts store should have the trailer parts you need to perform the repairs and replacements mentioned above.