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What Is a Hydraulic Caliper?
A hydraulic caliper converts fluid pressure into controlled clamping force on a brake disc. Inside the caliper, one or more pistons move outward when pressure rises in the hydraulic line, pushing the pads against the rotor to slow the wheel. Although trailer calipers are typically more compact than those on tow vehicles, the principle is the same and reliability is critical. A seized or leaking caliper reduces overall braking performance and compromises safety.
Types of Hydraulic Calipers for Trailers
Single-piston calipers offer a simple, cost-effective design suited to many light and medium-duty trailers. They are easy to service and widely available.
Twin-piston calipers increase pad area and clamping uniformity, providing stronger braking for heavier duty applications and higher axle ratings when matched correctly to discs and hubs.
Cast iron calipers are durable and economical. They are a strong choice for general inland use where corrosion exposure is moderate.
Stainless steel calipers provide superior corrosion resistance. They are recommended for boat trailers and trailers used near the coast where salt exposure is common.
Cast Iron vs Stainless Steel Calipers
Cast iron calipers deliver robust, predictable braking at an attractive price point. Their main limitation is susceptibility to rust in marine environments if maintenance is neglected. Stainless steel calipers resist corrosion and maintain smooth operation for longer in harsh, wet or salty conditions. For boat trailers and coastal regions, stainless is the safer long-term choice; for general purpose and inland use, cast iron remains a proven, budget-friendly option. You can compare current options in our hydraulic caliper range.
How to Choose the Right Caliper for Your Trailer
Begin by matching the caliper to the trailer’s disc diameter and axle capacity so that clamp force and heat capacity are appropriate. Confirm compatibility with your actuation method, whether surge override or electric over hydraulic, and ensure hose and fitting interfaces are correct. Check that the overall braking capacity meets New Zealand requirements at your trailer’s GVM, including the use of a compliant breakaway system where applicable. If you are unsure, our team can help you select the right caliper for your hub, disc and actuator combination.
Maintenance & Service of Hydraulic Calipers
Regular inspection keeps calipers operating smoothly. Look for fluid seepage around pistons and hose connections, confirm that slides move freely, and remove built-up salt and road grime after use. Replace pads before they reach minimum thickness and renew seals if any leakage is detected. Fresh, correct-spec brake fluid protects seals and helps maintain consistent braking feel across the system.
Common Problems with Hydraulic Calipers
Sticking pistons often arise from corrosion or contaminated fluid and can cause one wheel to drag or brake unevenly. Uneven pad wear may indicate misalignment or restricted slide movement. A soft or inconsistent pedal can result from air ingress or worn seals that reduce hydraulic pressure. Early diagnosis and service prevent rotor damage and restore balanced braking.
Hydraulic Calipers in Bundled Brake Kits
Purchasing calipers as part of a complete kit ensures component compatibility and saves installation time. Our 2500 kg surge kits pair calipers with matched discs, hubs, lines and a surge coupling, while our 3500 kg electric over hydraulic kits include calipers, discs, hubs, hoses and an EOH actuator for heavier trailers. Bundled solutions reduce guesswork and help with compliance.
Where to Buy Hydraulic Calipers in NZ
Explore our selection of hydraulic calipers in both cast iron and stainless steel, or choose a complete hydraulic brake kit for a ready-to-fit solution. If you need assistance matching calipers to discs, hubs and your chosen actuation system, contact the Treadway team for expert guidance.