How To Test That Demco Hydraulic Brake Actuator DM72VR Is Working Properly

Published 08/13/2021

Question:

I just installed a dm72 vr on a 1998 four winns trailer. I thought it went okay but when I use a wooden bar clamp to compress the coupler back, the brakes do not tighten. But when I pull on the break away cable with the top plate off the brakes apply normally. Is there a better way to test the actuator or am I missing something? Thanks much.

asked by: Jim M

Expert Reply:

Since the break away lever on the top plate activated the trailer brakes on your 1998 Four Winns Trailer it sounds like brake fluid is at least getting sent to your brakes which means the master cylinder is working correctly.

Chances are when testing the coupler with a wooden clamp not enough force was added to the coupler to cause it to apply the brakes. This can be pretty difficult to test, so I recommend raising one wheel of the trailer while blocking the other wheels, and having a friend manually engage the coupler. A long 2 x 4 or something similar may be needed to get enough leverage to activate the master cylinder.

You should try to spin the wheel once the actuator is engaged, and it should not spin.

Another option would be hooking the trailer up to your tow vehicle, and taking it for a drive to see if you feel the trailer pushing the vehicle when stopping, or if you can feel the brakes working. You wouldn't want to go on a busy street, but would want to find an empty parking lot to test this.

I included a video of the # DM72VR for you to take a look at.

expert reply by: Samuel C