The last two times I've had to tow my boat the trailer brakes were dragging after a few stops. The last time the brakes locked up solid and I had to crawl under the trailer and crack a bleeder to release them. The trailer is a 2004 eagle with tandem axle Kodiak disc brakes and titan surge tongue. Calipers, rotors and brake fluid were replaced last year due to wheel bearing failure. The brake fluid looks nasty, moisture contamination? Bad master cylinder? Any input is appreciated.

Could be sticking caliper piston, surge brake cylinder. The nasty fluid is not helping. How old are the calipers? I went with the full stainless caliper and rotor kit 2-3 years ago. They still look like new. Worth the extra $$$.

they were replaced june of 2018. when I cracked the bleeder all 4 calipers released.

Bad master cylinder? ...sounds like it to me

Was it a disc brake system before, or did you change over to disks from drums?

Original disc. Replaced with OEM brakes from kodiak.

Agree

Remove the master cylinder and disassemble, then clean and flush

If you have a backup solenoid, it may also be clogged up

Im gonna try to do that this week. I'd rather clean everything and flush it and try it before I just start throwing parts at it.

Is the coupler returning to full out when towing
There should be some type of return spring that keeps coupler relaxed until braking.
solenoid is only active when backing up to release pressure.
My suggestion flush the fluid, but leaning towards master cylinder if coupler moves correctly.

I'm not sure. I gotta take it apart. Just wanted to get a few ideas here of what to look for.