Four year old trailer with four wheel surge disc not working at all. Not even when manualy put into Brakes on Dont tow setting. The rese. is full, lines look good. Mostly fresh water dunked. What could it be. Thanks.

I would try and bleed them first and that will tell you if there is any air in the lines plus prove whether or not the system has any pressure.

If all is good there I would look at the brakes on the hubs for problems but unlikely that all four are bad.

Good luck

Thanks I'll give it a try.

Master cylinder might be bad. They are about $100.

I had a lockout solenoid go bad and cause the same symptoms. Another thing to check if everything else pans out.

Ditto - I had a neighbor at the lake with exactly the same problem on an almost new trailer.

throw some electric brakes on and forget about it, you wont be sorry for the extra jack you spend.