Take the master cylinder plug off the top and operate the plunger from the screwdriver access hole on the bottom of the actuator. By holding up on the brake release bracket with one hand and operating the pushrod with the other, you should see a swirl or movement in the master cylinder reservoir. If you operate the pushrod and not hold up on the release bracket the brakes should lock. If you can still roll the trailer in the locked position the master cylinder is not operating or needs to be rebled. Replacement master cylinders are available through Waymires, 1-800-434-4824 or www.waymires.com
. Be sure to specify drum or disc brake. To change the master cylinder, disconnect brake line from under the actuator, and the blue solenoid wire if it is disc brakes. Then remove the 2 clips and washers from one side of the outer member and push the pins all the way out the other side. The inner member will now slide out the front. As you pull the member out, keep one of the pins in your hand and put it back in as each hole clears the outer member. This way you will have the whole thing still assembled to take to the bench. To change the master cylinder from this point, flip the whole thing upside down and remove the rear pin, then depress the brake release lever (just behind the ball socket), and pull the master cylinder/pushrod assembly out and flip them over to access the bolt that holds the pushrod to the master cylinder. Now the master cylinder can be exchanged with a new one. If you had a solenoid on the old one, remove and replace on new one using a zip tie on the bypass hose.