Surge brakes sticking

The brakes on my trailer seem to be sticking or locking up, when I hit the brake in my truck the trailer brakes pretty much lock and skid. They are just basic surge brakes, so no brake controller or anything like that. Any idea what the problem is?

Most likely rusted caliper creating friction with the piston or trash in your lines.
What brand brake caliper / rotor do you have?

I'll have to check on the brand. The trailer is a Sportsman (for a Sanger).

It also locks up in reverse backing up my driveway. I kinda looked into a solution for that but doesn't seem like the two problems are related from my research

I have same trailer. You have to lockout the ram on the brake actuator right at the hitch. Two ways to do that 1) use the mechanical lockout that is hanging by a small cable on the tongue and 2) tie in the electrical circuit to your backup lights - this will lockout the ram automatically each time you backup (preferred method)

As to the brake sticking, I'd check the guide pins and seals on the calipers. Sounds like the pads arent free to float as they should be.

Do the trailer have a 5 pin plug for the lights? The 5th pin is to disengage the trailer brakes while backing.

How many tires are locking and skidding?

So I dug into this more today. It was low on fluid so I bled the system but that didn't solve the problem. I tried adjusting the brakes with the starwheel (they are drum brakes) but it never got tight enough, even when adjusted all the way.

It seems like it has no brakes until you push hard enough on the tow vehicle brakes then it locks up. It releases when not on the brakes, but skids the tires with any moderate braking action.

I guess next step is to pull the drums off and see what's going on inside

I had the same issue with my SportBoat trailer on my sanger. If I gave it 3/4 braking due to an unexpected yellow light or someone pulling out in front of me they would lock up. I sold the boat but was considering just locking them out permanently since it wasn't that heavy of a tow. Sounds like system may need to be bled and like someone said maybe do a fluid flush to get new brake fluid in the whole system. Also try and hit the brakes a few times in reverse with a bit of speed since drum brakes self adjust that way. At least those are the cheap ways to try before tearing it down. I was never impressed with the sportboat trailer other than they look nice.

PLEASE LISTEN TO ME!!

After several years of battling surge actuated brakes on my trailer i finally switched to electric. I was having major brake issues two or three times a year where i was laying on the road trying to adjust the brakes to prevent lock up. Flat spots on my tires and replacing tires several times. Since switching to electric i have had ZERO issues for 3 years. If you are in any way mechanically inclined you can do the swap yourself. The only difficult part was welding the surge mechanism and then having to paint that part of the trailer. My $0.02