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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
Looks like a quality part Fit exactly where the old one came out
Part fit perfect!!!!!
Fast delivery. Good product. Will buy here again and recomend my friends do the same.
Still working great after 1 year !
Really helpful
the solenoid failed I need to replace a gain.
It was a perfect replacement
This product will help when backing up the trailer. Replaced original perfectly.
Excellent Product and price,fit perfect,thanks for your speedy service.
Johnk
3/11/2018
Product worked just find!
Master cylinder fit perfectly. Great customer service. Thanks.
In less than one year the reverse solenoid went out. I saw in another review this same issue happened. My solenoid was wired directly to the vehicle ground supply and is getting 14.3 volts.
Your company did what it said it would, in a very timely time..The lights were as I needed, would buy from you again.. The brake cylinder also fits my trailer and the price was right.
Needed a new master cylinder for my boat trailer. They had it in stock and shipping was fast. Will definitely use ETRALIER in the future.
The initial product had a problem with the solenoid after about 6 months after installation. The solenoid did not respond to the 12V reverse signal. Although customer service could not replace the total unit, they were able to have the vendor send a replacement solenoid at their expense. The solenoid showed up later than promised, however, it did respond to the 12V signal. The unit now works. I now see that the solenoid can now be purchased individually. Thanks for the opportunity to share this review and I appreciate customer service helping to resolve this issue.
Still working perfectly!
Ordered wrong one first for a drum brake system, E Trailer helped me return and then ensured I got correct for disc brake system. The polymer housing is interesting but probably better for a boat trailer. Installation went smoothly , bled system with no issues and now trailer has brakes again. Very happy with this part and etrailer!
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?
Sara was a Great help.
we paid to have the part shipped via ups and you shipped it usps which caused issue with our customer because part did not come when expected and customer was not able to use his boat as expected. I tried to get help and kept getting the run around via emails.
Info for this part was:
At etrailer we provide the best information available about the products we sell. We take the quality of our information seriously so that you can get the right part the first time.
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.
Helpful Links
Accessories-and-Parts/Demco/DM5404.html