Trailer Brakes - Everything You Need to Know And Whether You Need Them Or Not

KT Trailers
Mar 9, 2023
5 min read

Updated: Jul 22

Introduction: What Are Trailer Brakes and Why Do I Need Them?

Trailer brakes are an essential safety feature that enhance control, improve stopping power, and help you tow with confidence. Whether you're hauling machinery, work gear, or your motorized toys — your vehicle’s brakes alone may not be enough. Trailer brakes work in conjunction with your tow vehicle’s braking system to provide safer, smoother stops, especially in emergencies or challenging road conditions like hills, wet roads, or strong winds.

Why Trailer Brakes Matter

Whether you're towing for work or leisure, brakes on your trailer help:

Distribute braking load, reducing stress on your tow vehicle
Improve stability, especially when braking suddenly or descending steep hills
Meet legal requirements, which vary by region and trailer weight
Prevent accidents, especially at higher speeds or in wet conditions
Extend the life of your tow vehicle’s brakes, tyres, and driveline

How to Determine if Your Trailer Needs Brakes

In New Zealand, the legal requirements for trailer brakes depend on the trailer's Gross Laden Weight (GLW)—the total weight of the trailer plus its load. Here's a breakdown:

Trailers Up to 2000 kg GLW

Brakes: Not legally required. However, if brakes are fitted, they must be in good working order and act on each wheel of at least one axle.
Safety Chains: At least one safety chain is mandatory.
Performance: The combined vehicle and trailer must be capable of stopping within 7 meters from a speed of 30 km/h.

Trailers Between 2001 kg and 2500 kg GLW

Brakes: Required on at least one axle. These can be either direct (cab-controlled) or indirect (override) systems.
Safety Chains: Two crossed safety chains are mandatory unless a compliant breakaway brake system is fitted.
Performance: Must meet the same stopping distance as above.

Trailers Between 2501 kg and 3500 kg GLW

Brakes: Direct (cab-controlled) service brakes are legally required.
Parking Brake: Must act on at least one full axle and be capable of holding the trailer at rest on a slope of 1 in 5.
Breakaway Brake: Mandatory. If a breakaway brake system is installed, safety chains are not required.

Clarifying Common Misconceptions

The 2000 kg Brakes Requirement: Legally, in New Zealand, trailers do not require brakes until they exceed 2000 kg GVM. However, most tow vehicle manufacturers specify that trailers over 750 kg GVM should have brakes to ensure safe towing and to avoid voiding warranties. So, even though the law allows unbraked trailers up to 2000 kg, in practice, trailers over 750 kg typically need brakes to comply with vehicle manufacturer recommendations and for safer towing.
Breakaway Brakes vs. Safety Chains: For trailers between 2001–2500 kg GLW, you can use either a breakaway brake system or two crossed safety chains. For trailers over 2500 kg GLW, a breakaway brake system is mandatory, and safety chains are not required.

What Type of Brakes Are Available — and Which is Right for You?

There are three main types of trailer brakes, each with different advantages depending on your setup, terrain, maintenance preferences, and towing habits.

Hydraulic brakes

Common in boat trailers and older trailers

How they work:

Braking pressure in the tow vehicle pushes a piston in the trailer coupling, activating hydraulic pressure in the brake lines to engage the trailer’s brake drums or discs.

Pros:

Responsive, progressive braking when maintained
No electrical wiring required
Suitable for wet environments like boat ramps
Often used with disc brakes which perform well in water

Cons:

Can feel jerky if the system isn’t tuned correctly
Requires manual lockout (flip pin or override valve) for reversing
Maintenance needed: checking for leaks, air in the lines, or worn seals
Repairs can be more expensive than mechanical or electric setups

Note: Newer systems may include reverse solenoids to eliminate the need for a flip pin when reversing.

Electric Brakes

Most commonly used on medium to heavy trailers

How they work:

Electric brake magnets engage when current is sent from the tow vehicle’s brake light circuit via a brake controller. At KT Trailers, we simplify this with our on-drawbar mounted electric brake controllers — no hardwiring to your vehicle cab required.

electric brake controller, mounted on draw bar of trailer — Electric brake contoller

Pros:

Smooth, adjustable braking force via controller
No mechanical lag
No need to exit the vehicle when reversing
Great for towing variable loads or long distances
Easy diagnostics and adjustments

Cons:

Requires electrical connections between tow vehicle and trailer
Sensitive to corrosion or poor wiring if not well-maintained

Mechanical (Cable) Brakes (Designed for 3.5T GVM Trailers)

Also known as: European Mechanical Overrun Brakes

How they work:

This is not your typical old-school cable brake setup. The system used on our 3.5T trailers is a purpose-built, precision-engineered mechanical overrun brake that provides smooth, proportional braking without the complexity of electronics or hydraulics. When the tow vehicle slows, the inertia of the trailer activates a sliding coupling head, which pulls a high-tensile brake cable linked to robust brake drums. The internal auto-reverse feature ensures the brakes disengage during reversing, eliminating wheel lock or dragging.

Why it’s different: This system is specifically designed and rated for heavy-duty 3.5T applications — not repurposed from smaller trailers. It delivers consistent, confidence-inspiring braking, even when fully loaded, and is known for its smooth towing characteristics, making it an excellent choice for commercial and agricultural use.

European mechanical braking system on a flat deck trailer — European mechanical braking system

Pros:

Engineered for trailers up to 3500kg GVM
Smooth, progressive braking — ideal for long hauls and frequent stops
No need for vehicle wiring or in-cab brake controllers
Auto-reverse hubs make backing up hassle-free
Integrated mechanical handbrake and breakaway cable for added safety
Low-maintenance and built tough for NZ conditions

Cons:

Braking force is not adjustable like electric setups
Cable tension needs occasional checks for optimum performance

Best for: Operators who want a robust, legally compliant, and easy-to-maintain braking system without sacrificing towing comfort or control.

Maintenance Tips for Trailer Brakes

To keep your braking system safe and effective:

Inspect regularly: Check pads, drums/discs, cables, and fluid (if hydraulic) every 6 months or before major trips
Test function: Apply brakes before setting off to make sure everything is working as expected
Keep it clean: Wash brake components (especially after saltwater exposure) to prevent corrosion
Look for signs of wear: Unusual noises, pulling to one side, or inconsistent braking should be investigated
Service by professionals: If in doubt, get your brakes checked by a certified trailer service provider

Troubleshooting Common Brake Issues

Problem	Likely Cause	Suggested Action
Brakes feel weak	Worn pads/shoes, air in hydraulic lines, loose cables	Inspect and replace or bleed system
Brakes lock up	Over-tightened mechanical cable, faulty controller setting	Loosen adjustment or recalibrate
Brakes not activating	Electrical fault, broken cable, seized actuator	Test connections, replace worn parts
Trailer hard to reverse	Hydraulic system without reverse lockout	Add solenoid or use lockout pin (and remember to remove it after!)