Trailer brake locks up when empty

There's no ABS sensor on this axle

 

Remove the Honda Civic from underneath and wheels should rotate freely

 

Sounds like you've got a 2S/2M ABS system. 1 sensor and 1 modulator valve per side controlling both wheel ends on that side. Going out on a limb I'm guessing the axle that's locking up is the one without speed sensors?

 

That's correct

 

What's happening (if you do indeed have a 2S/2M system) is that the system can only read the speed on one axle. The ABS system has no idea what the other axle is doing. The theory behind the 2 sensor/2 modulator system is that it assumes both wheel ends on the one side will have similar amounts of traction. The modulator valve regulates air pressure to both wheel ends on the same side based on the speed signal from the single sensor on the one axle.

 

That would make you inside out. Would it not?

 

We used to have a lot of trouble with locking up trailer brakes when empty even with 4S/2M ABS. Ended up switching from Abex 685 23K lining to Abex 6008 20K lining. No one has complained about increased stopping distance and tire flat spotting has been greatly reduced.

 

What is abs? I always had light on dash but I pulled the bulb out

 

You are joking right?
ABS Anti lock Brake System

 

Yeah bro. But not joking about taking the bulb out