Bleeding Brakes After Replacing Surge Brake Actuator

Updated 09/24/2026 | Published 09/19/2026

Question:

I just put a DM8104311 actuator on my boat trailer. I have tandem axles with two bleeders on each caliper. And I’m not sure how to bleed the brakes.

asked by: Glen

Expert Reply:

Thanks for letting us help Glen. I'm going to include a link below to a help article we put together that walks through the surge brake bleeding process in detail.

This job is much easier with two people. One person can operate the actuator and keep an eye on the master cylinder while the other works at each brake caliper. It's very important to keep the master cylinder topped off with brake fluid throughout the entire process. If the reservoir runs dry at any point, air will be pulled back into the system and you'll need to start the bleeding process over. You'll want to begin with the caliper farthest from the actuator, which will be either caliper on the rear axle. From there, move to the opposite rear caliper, followed by the two calipers on the front axle, working your way progressively closer to the actuator. Since your calipers have two bleeder screws, use the upper bleeder screw. Air rises inside the caliper, so bleeding from the upper screw allows trapped air to escape properly.

Continue bleeding each caliper until you're getting a steady stream of clean brake fluid without any air bubbles, while making sure the master cylinder never runs low.

Any plans for your boat once you get your maintenance done?

expert reply by: Christopher H

Alan R.

9/23/2026

Before you start trying to bleed the calipers you must bleed the master cylinder first. The best way is disconnect the coupler shocks and add a short brake line from the brake master cylinder outlet and return the brake fluid back to the master cylinder. Pump the drop hitch until you get a clear fluid with no bubbles. After you get the master cylinder bled you remove the short brake line and connect the main brake line that runs to the calipers.if you miss this step it is extremely difficult to bleed the brakes. Then attach a pressure bleeder to the master cylinder and then start bleeding the calipers. It may take several times to get all the air out of the system. After you think you have all the air bubbles out then remove the pressure bleeder and reconnect the shocks. Road test to confirm the brakes are operating tonight have to renewed the system. It could take several times to get it right. Good luck with the project. When mounting the coupler to the trailer make sure you install all the bolts. Three 1/2 inch and two 5/8 stainless steel bolts.

Christopher H.

9/24/2026

@AlanR Really appreciate all of the detail here. Very helpful! Sounds like you've done this once or twice.

Alan

9/24/2026

@ChristopherH Another tip on bleeding calipers especially after installing new calipers. After the calipers are mounted use a pressure bleeder to fill the calipers before you start bleeding the brake system. Connect the pressure bleeder to the lowest bleeder screw and open the top bleeder screw to fill the empty caliper. This saves you a ton of time and aggravation. Regards: