Need some help please with trailer brakes locking sometimes

[tsuprum]

Hi, I have a 1987 ranger trailer. Single axle with disc brakes. The brakes, rotors and calibers are relativly new. This started last season:

I will be driving along and the brakes will start smoking. I'm guessing there locking up. So I stop let them cool down a bit. If I backup like 10ft it releases the locking. I can then usually go good until I have to stop. Then sometimes they lock again.
I noticed that if I backup first after stopping I'm usually good to go.
Anyone have any idea what this could be.

Thank you, Tony Suprum

[CatFan]

Does it happen after braking or just while going at a steady speed on flat ground?

If after braking, I'd be looking for a kinked line.

Is your hitch level?

[tsuprum]

When I'm travling on the highway it can happen anytime. If I'm on local roads and stopping it will happen more but not ever stop.
I will check the hitch level. I have a drop hitch but maybe it's not level enough.
That is something I didn't think of. Thanks

[DABS]

sounds like trapped fluid in the line. Putting it in reverse re-directs the fluid back to the master cylinder. May be time for a new master cylinder.

[tsuprum]

Great, thank you. I will check the MC.
This is one of those problems that drive you crazy as it doen't happen all the time

[DABS]

It's most common when the trailer has been parked without pulling the actuator back out. Once the actuator is stretched out, the piston in the master cylinder is against the snap ring and protects the honed sleeve from rust or corrosion. Usually this will occur after the trailer has been parked for a period of time. You can try cleaning out the master cylinder by pulling the piston in the bottom and cleaning the bore. If you actuate the piston with a screwdriver through the access hole on the bottom, you should see swirling in the reservoir where the fluid is delivering, and returning to the reservoir. If no swirl, replace the master cylinder.