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Master cylinder with bypass installs in your Demco actuator and wires into your tow vehicle so that your trailer brakes won't activate when you shift your vehicle into reverse. For use with Demco hydraulic surge-type disc brake actuators.
Features:
Specs:
Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.
Jeff: Hello everybody, this is Jeff at etrailer.com. Today we're going to take a look at the replacement disc brake master cylinder with the bypass electric lockout for Demco actuators. Now this replacement master cylinder is designed for use with the Demco trailer brake actuators that have the electric reverse lockout. It is designed to work with the Demco brake actuator model DA66D, DA86, the DA91, the DA10, the DA16, and the DA20 models. This is an electric reverse lockout, it'll let you back up without activating your trailer brakes.The solenoid right here will activate automatically when you shift into reverse. You can see the two wires, there's two black wires here, one will connect to a good clean ground, the other connects to the reverse light circuit and the wires are both black wires so either wire will connect to either function.
This does have the bypass configuration. Now the measurement up at the top, the bolt holes here, they measure center to center, three inches by two inches, and the overall dimensions at the top, it's going to be right at four and a half inches by three and a quarter inches.But that should do it for the review on this replacement disc brake master cylinder with the bypass electric lockout for Demco actuators.
Customer Satisfaction Score:
93% were satisfied with this product
7% of customers were not satisfied
Ratings & Reviews
Kate F.
7/13/2026
Sorry to hear the first one was wrong, but glad to hear we could help make it right Joseph! What kind of boat do you have, and what body of water are you out most on?
Johnk
3/11/2018
Product worked just find!
Mike L.
11/7/2018
I spoke with my contact in the Tech Support department at Demco, who tells me its pretty rare for those solenoids to fail after only one year. What is much more likely is that the solenoid is not getting sufficient power, or the ground connection isnt secure enough. Instead of grounding the solenoid to the trailer frame, tie it into the ground for the trailer connector which will ensure a good ground connection. Youll also want to check the solenoid power feed and make sure youre getting a full 12-volts. If its not a wiring issue and the solenoid needs replacing, we carry a replacement as part # DM5404.
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Michael
10/6/2026
Still working perfectly, very pleased!