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Electric trailer brakes not working, or one wheel locking

When electric trailer brakes are weak, dead, grab, or lock one wheel, the cause is usually adjustment, the controller setting, a wiring fault, or worn magnets. Typical prices around Ocala: adjustment $80 to $150, new brake assemblies $350 to $600 per axle. Check the controller and the plug first; they cost nothing to look at.

Check this first

  1. Look at the controller. With the trailer plugged in, does the controller in the truck show a connection? Squeeze the manual lever: does the readout move? No connection means the fault is between the controller and the trailer.
  2. Check the gain. Dexter says best braking is a controller setting just short of wheel lockup. Too low feels like no brakes; too high locks wheels, especially empty.
  3. Clean the plug. Corroded pins in the 7-way plug cut the brake circuit just as they cut the lights.
  4. Think about the load. If a wheel locks only when the trailer is empty, insufficient wheel load is on Dexter’s list of causes. Turn the gain down for empty runs.
  5. Feel the hubs after a short drive (carefully, they can be hot). One hub much hotter than the others can mean a dragging brake.

What is usually wrong

SymptomCauses, per Dexter’s troubleshooting chartTypical fix and cost
No brakesOpen circuit, under-adjustment, faulty controller, short circuit, corroded connectionsTrace and repair $100-$200; adjust $80-$150
Weak brakesUnder-adjustment, glazed linings, grease on linings or magnets, worn magnets, overloaded trailerAdjust $80-$150; new assemblies $350-$600 per axle
One wheel locksInsufficient wheel load, loose or broken parts, out-of-round drums, controllerAdjust controller; repair parts
Pulls to one sideWrong magnet lead wire, incorrect adjustment, grease on linings, broken wires, bad connectionsAdjust and repair
IntermittentBroken wires, loose connections, faulty groundTrace and repair, $100-$200
DraggingOver-adjustment, out-of-round drums, faulty breakaway switch, loose bearing adjustmentReadjust; repair

Full ranges are on the pricing page.

Why it happens

Dexter’s schedule says to adjust brakes after the first 200 miles, then every 3,000 miles, and to inspect magnets every 6 months or 6,000 miles. A trailer that hauls on and off for years without that drifts out of adjustment one wheel at a time. On trailers that sit outdoors, magnets and drum faces rust. Dexter says magnets must be replaced if worn unevenly or if the coil shows through, and replaced in pairs on an axle.

Why it matters

Florida requires brakes on all wheels of any trailer over 3,000 lb gross (s. 316.261(3)) and breakaway brakes that stay applied at least 15 minutes (s. 316.261(4)). A horse trailer that cannot stop itself is a danger to the horses and everyone around them.

When to call

If the controller and plug check out and the brakes are still wrong, it is time to pull the hubs. That is also the cheapest time to do the bearings. See trailer brake repair, wheel bearing service, and the bearing and brake calculator. If the breakaway is the problem, see breakaway battery dead or not holding.

Frequently Asked Questions

Why does only one trailer wheel lock up?

Dexter's troubleshooting chart lists insufficient wheel load, loose, bent or broken brake parts, and out-of-round drums, plus a controller set too aggressively. An empty trailer has less weight on each wheel, so it locks a wheel more easily.

Why do my trailer brakes do nothing?

Dexter lists open circuits, under-adjustment, a faulty controller, short circuits, grease or oil on the magnets or linings, and corroded connections. The controller and plug are the first things to check.

What does it cost?

A brake adjustment runs about $80 to $150 for the trailer. New electric brake assemblies, both sides, run $350 to $600 per axle.

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