A loaded trailer that pushes against the tow vehicle, pulls to one side or develops a hot hub is not a problem to leave until the next service. This trailer brake maintenance guide covers the checks that help keep plant trailers, car transporters, builders’ trailers and general-purpose trailers working safely. Most faults start small: a seized cable, contaminated shoe lining, weak breakaway battery or neglected bearing adjustment. Catching them early is cheaper than replacing hubs, drums and tyres after a roadside failure.
Start with the brake system you have
Before ordering parts or adjusting anything, identify the braking arrangement. Most braked trailers in the UK use an overrun coupling. When the towing vehicle slows, the trailer’s drawbar compresses and applies the wheel brakes through rods, cables and compensators. Some specialist trailers use hydraulic brake systems, while electric brakes are also found on certain imported and specialist applications.
The service approach changes with the system, but the basics do not. The brake must apply evenly on both sides, release fully when the trailer moves forward, and hold the trailer securely when parked. If one wheel is doing all the work, stopping performance suffers and the overloaded side wears quickly.
Check the trailer manufacturer’s handbook for the specified brake components, tyre pressures and service intervals. Axle and brake ratings matter. A part that looks right is not necessarily correct for the axle, drum diameter or gross trailer weight.
Trailer brake maintenance guide: the regular walk-round
A quick check before towing is worthwhile, particularly where trailers are shared across a yard or used hard on site. Walk around the trailer with it coupled, then uncoupled where safe to do so. Look for damaged cables, bent linkage, loose fasteners, cracked brake pipes and signs of grease or fluid around the wheels.
Operate the handbrake and feel for a firm, progressive pull. A handbrake that comes up excessively high may point to worn brake shoes, stretched cables or poor adjustment. One that feels solid but fails to hold can indicate seized linkage or contamination inside the drum.
With an overrun coupling, inspect the drawbar gaiter and slide mechanism. It should move smoothly, without heavy corrosion, excessive play or a harsh clunk. The damper should control the drawbar movement. If the coupling shoots in and out freely or remains compressed, investigate it before towing. Do not compensate for a sticking overrun unit by overtightening the brake cables.
The breakaway cable also needs attention. It should be routed so it can apply the trailer brakes if the trailer separates, without dragging on the ground or becoming tangled around the coupling. Replace it if strands are frayed, the clip is distorted or corrosion has weakened it. On trailers fitted with a breakaway battery, test the charge and terminals as part of the same routine.
Inspecting drums, shoes and hubs
A proper brake inspection normally means removing the wheels and drums. Support the trailer securely on suitable stands on level ground. Never rely on a jack alone, and chock the wheels that remain on the ground.
Once the drum is removed, inspect the brake shoes. The friction material should be securely bonded or riveted, evenly worn and free from cracks. Replace shoes as an axle set, not one side only, to keep braking balanced. A shoe that is glazed, oil-soaked or badly scored will not regain reliable performance simply by adjustment.
Look closely at the drum’s braking surface. Light marking can be normal, but deep grooves, heat checks, blue discolouration or an oval drum need further attention. A drum worn beyond its permitted limit must be replaced. Measure it against the manufacturer’s maximum internal diameter rather than making a judgement by eye.
Grease on the shoes usually comes from a failed hub seal or incorrect bearing greasing. Brake cleaner may remove surface residue, but it does not make contaminated linings dependable. Replace the affected shoes, cure the source of the leak and inspect the bearings before putting the drum back on.
While the drum is off, check the wheel cylinder on hydraulic systems for dampness around the seals and dust boots. Any fluid leak calls for repair before use. On cable-operated brakes, check the expander mechanism, return springs and adjuster. Springs lose tension with age and corrosion, and a weak return spring can leave a brake dragging after release.
Cables, rods and compensators need free movement
Overrun brakes rely on mechanical movement from the coupling to each wheel. This is why cables and linkage deserve more than a quick glance. Outer cable sheaths should not be split, crushed or corroded. Inner cables should move freely without sticking. If a cable binds, replace it rather than flooding it with lubricant and hoping it lasts.
Check equaliser bars and compensators for straightness and free pivoting. A seized compensator can make one brake apply ahead of the other. The trailer may then pull or snatch under braking, even though both wheels appear to be fitted with serviceable parts.
Lubricate only the points specified by the manufacturer. Grease has a place on pivots and certain coupling components, but it has no place on brake linings, drums or cable friction surfaces unless the instructions specifically call for it. Excess grease attracts grit and can create another fault.
Adjustment comes after inspection
Brake adjustment is often misunderstood. It is not a substitute for replacing worn parts. Adjust only after the shoes, drums, cables and linkage have been checked and confirmed serviceable.
On many drum brake assemblies, the adjuster is set at the wheel first. Turn it until the shoes contact the drum, then back it off enough for the wheel to rotate freely with only slight, even drag if specified by the manufacturer. Repeat on both sides. The precise method varies by axle manufacturer, so use the correct procedure for the brake assembly.
After the wheel brakes are set, adjust the linkage so there is no excessive slack but the brakes release fully. Test the overrun coupling and handbrake again. If the wheels drag after a short road test, stop and correct the adjustment. Dragging brakes generate heat rapidly and can damage bearings, grease seals and tyres as well as the brake components themselves.
Bearings and brakes should be serviced together
A brake service is the sensible time to inspect wheel bearings because the drum or hub is already removed. Spin each hub, check for roughness and feel for play. A rumbling bearing, damaged race or excessive movement needs attention before the trailer returns to work.
Bearing adjustment is especially important on taper roller bearings. Too loose and the hub can move, affecting brake operation and damaging the seal. Too tight and the bearing overheats. Fit new seals where required and use the correct grease sparingly. Packing a hub indiscriminately with grease can force lubricant into the brake drum.
After reassembly, tighten wheel nuts to the trailer or wheel manufacturer’s stated torque using a suitable torque wrench. Recheck them after the first journey following wheel removal, particularly on a newly serviced trailer.
Know when a professional inspection is the right call
Routine checks and replacement of like-for-like service parts are within reach of experienced owners. However, it is worth using a competent trailer workshop where there is uncertainty over axle ratings, hydraulic bleeding, damaged couplings, cracked mounting points or repeated uneven braking.
Do not ignore warning signs because the trailer is only used locally. A burning smell, smoke from a wheel, brake fluid loss, a sudden change in overrun action or a trailer that will not hold on the handbrake all justify taking it out of service. The cost of downtime is usually lower than the cost of a recovery, damaged load or collision.
Keep a simple record of brake inspections, adjustment, parts fitted and any defects found. It helps when more than one person uses the trailer, and it makes recurring faults easier to trace. For trade users, keeping common wear items such as brake cables, breakaway cables, wheel bearings, seals and suitable hand tools available can prevent a small defect from holding up a job. A trailer that stops straight, releases cleanly and holds securely is one less uncertainty when the working day is already full.