Purchased a boat last year, was told the master cylinder needed replacing. Didn’t get to messing around with it till now. The master cylinder was empty so I filled it, pushed the coupler in and tried bleeding the brakes.... didn’t go so well. The farthest brake gave me a couple of drops, while the other one gave me nothing. I’m guessing there’s a blockage, probably rust somewhere between the first brake and the master cylinder. So what do I do and where should I start?

Did you look inside the master cylinder before you filled it? Was there any sludge in the bottom. My old one was full of sludge, so I went to EOH.

Probably easier to replace the master cylinder, flush or replace all the lines and just for good measure, if drum, replace backing plates with all new loaded up and ready. Just bolt on, bleed them and go. If you have disc, new calipers and pads would be in order. Not really that expensive to do it all and you will know what you have.

can be a few issues..did you try vacuum bleeding the lines???

Also, If the master was dry of fluid and the brakes were used (well.... applied) it could have damaged the seals on the piston = proper pressure isn't delivered down the lines/ no pressure being developed = swap out to EOH.

I gave up on surge brakes many years ago. Converted to all electric just like all of my other trailers. All I do is unplug the trailer at the ramp. Other than that it's all the same and way more reliable.

Before you start replacing the complete brake system buy a power bleeder. https://www.summitracing.com/parts/m...RoCGqUQAvD_BwE

You can pressurize the brake system and crack open the hoses to see if you have flow or not at each location. This will let you know what you have to work on, possibly change.