Which lockup pattern do you have?
| Pattern | Likely first area |
|---|---|
| Every wheel grabs with pedal/manual lever | Gain, boost, synchronization, controller mode or output |
| One wheel locks before the others | That wheel's adjustment, hardware, drum, magnet or bearing |
| Brakes stay applied with no command | Breakaway switch, short-to-power, connector contamination or wiring error |
| Lockup appears only on bumps | Intermittent wiring, loose components or unusual controller/mounting issue |
If every brake locks
Start inside the tow vehicle. Confirm the controller is set for electric rather than electric-over-hydraulic brakes. Return gain, boost and synchronization settings to the controller maker's setup path instead of guessing. A trailer loaded differently from the last trip may need a different setting.
Dexter's service guidance warns that locking and sliding tires is generally undesirable because it can flat-spot tires and reduce control. The goal is synchronized, firm braking—not proving that maximum gain can skid the wheels.
If only one wheel locks
Do not reduce whole-trailer gain until three good brakes are too weak. The controller does not normally choose one wheel; a one-wheel symptom points to that wheel position.
- Brake adjusted much tighter than its mate
- Broken, stretched or misplaced shoe spring
- Seized actuating lever or damaged adjuster
- Loose or bent internal component
- Out-of-round or damaged drum
- Contamination that makes application inconsistent
- Bearing looseness affecting drum alignment
Support the trailer by its approved procedure and inspect the brake and bearing together. Do not blow brake dust with compressed air.
If the brakes stay on without the pedal
Confirm the breakaway pin is fully seated and its cable is not pulling the switch during turns. Inspect the switch for impact or corrosion. Then inspect the seven-way for moisture and cross-contact and the brake-output wire for a short to an auxiliary power source.
A brake controller may send a tiny sensing signal to look for the trailer; that is different from enough continuous output to apply the brakes. Use the exact controller's diagnostics rather than assuming any measured voltage is a fault.
Heat tells you whether the brake released
After the trailer is safely stopped, compare the same location on every hub without touching it. One wheel far hotter than its peers supports a local drag problem. Smoke, burned paint, a strong odor, grinding or looseness makes it a travel stop requiring disassembly.
After a repair or adjustment
- Verify every wheel rotates and releases according to the axle manual.
- Confirm the controller shows no open, short or overload fault.
- Set gain with the loaded trailer in a traffic-free area.
- Make smooth stops and compare hub temperatures.
- Complete the brake maker's burnish procedure if friction parts were replaced.
FAQ
Why do all brakes lock at low speed?
Gain, boost or synchronization may be too aggressive, or the controller may be in the wrong brake mode. Follow its setup procedure before changing mechanical adjustment.
Why does one wheel grab?
Inspect that wheel for adjustment mismatch, loose/broken hardware, drum damage, contamination and bearing condition.
Can the breakaway switch keep the brakes locked?
Yes. If its pin is pulled or the switch/wiring is damaged, the dedicated battery can energize the brake circuit. Repair and test the complete breakaway system before towing.
Related brake help
- Complete trailer-brake troubleshooting guide
- Trailer brakes weak at high gain
- One trailer wheel is hot
- Breakaway switch test
Sources and review notes
Reviewed July 18, 2026. Controller gain, boost, mounting and test procedures vary. Mechanical adjustment and wear limits come from the exact axle manual.
All wheels, one wheel or no command?
Choose the exact pattern in the towing troubleshooter for a shorter test path.
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