Dexter brake actuator install

At last!  The new brake actuator arrived yesterday and with the help of friends it was installed today.  We’re back in action!

Those of you who followed the saga of our aborted trip to California know that our third Actibrake disc brake actuator quit without notice recently.  I’ve had a long and painful history with that product, which you can read about in the Tour of America archives and the Man In The Maze archives.  Suffice to say that this time we chose to switch brands, and after some research into the various products I chose to go with Dexter’s brake actuator, model K71-651-00.  It’s a 1600 psi unit designed specifically for disc brakes.

When the new actuator arrived I was immediately impressed with its design.  It’s a bit smaller than the one it replaced, and has a less-complicated 4-wire installation process (12v+, ground, brake controller, breakaway switch).  The previous one required five wires and I’ve seen some competitors that need six or more.

The mounting feet are integrated into the cast aluminum case, so I was able to toss the funky hold-down straps that we’d used before.  The whole thing seems tougher and neater, and from what I’ve read this Dexter unit has a good reputation for reliability, which is of course the highest priority in your braking system.

Removing the old dead unit was simple. The first step is to disconnect the trailer’s power, which means unplugging the trailer from shore power and removing the negative terminal on the battery.  Then I unscrewed the straps that held the brake actuator down, snipped the wires, and unscrewed the flexible hydraulic line.  It was out in five minutes, and it would have been quicker if I wasn’t working the confines of a closet.  I haven’t decided what to do with the old one yet.  My friend Rob suggested I send it to the Smithsonian.  I suppose it could be refurbished with a new circuit board but I don’t feel very good about passing on a proven unreliable product to someone else, given that I’ve had three of them fail.

Most of the job would have been fairly easy if it weren’t for that closet.  Having the actuator inside the trailer eliminates possible future problems from weather exposure, but it also means it ends up in some really awkward spot.  To get into the closet I had to lie on my side and wedge myself in, which was uncomfortable to say the least.  Fortunately, Rob came by and shared the joy by taking turns with me crimping wires in that tiny space (and he’s bigger than me).

The only other attachments needed were the hydraulic line, which just screws on with low torque (22 ft-lbs), and four wood screws to attach the Dexter to the floor. I pre-drilled the floor holes with a 1/16″ bit, screwed the actuator down, and we were basically done inside.

The next step is to fill the reservoir up with brake fluid, which required about a quart.  We reconnected the power, pulled the breakaway switch, and heard the reassuring hum of the actuator’s pump in full operation.

Once we knew it was working, we needed to bleed the air out of the brake lines.  This is the part I hate, because I have never managed to find a way to get a hose tightly on the bleeder valves so that it doesn’t leak.  I always end up with an armful of brake fluid, and this time was no exception.  But the bleeding went fairly quickly (there wasn’t a lot of air to be removed).  It definitely is crucial to have a buddy standing by at the breakaway switch to activate and deactivate the unit while you’re underneath getting doused with brake fluid.  We kept an eye on the fluid level but didn’t need to top it up until the bleeding job was done.  All told, we used about 1.5 quarts of DOT3 brake fluid to fill the reservoir and bleed the lines.

After that, the next task was to clean up the wires, which are a bit haphazard with different colors and multiple butt splices left from prior re-installations. The photo shows it before I wrapped things up.  I may also install a shelf so I have a flat surface above to store things, later.

At this point I lost my assistant, but the hard work was done.  All I need to do now is hitch up and go for a test tow.  When I do that, I’ll be checking that my previous brake controller settings still feel right for this controller (they probably will) and that I’ve gotten all the air out of the lines.  I’ll know if there’s air because it will take longer for the actuator to build up pressure and hence cause a delay in braking action.  Hopefully I got that part right.

If you are contemplating this job yourself, you’ll need these tools:

  • 2-3 qts of brake fluid
  • open-end wrenches to remove and re-attach the hydraulic line
  • brake bleeder wrench (5/16″ or 1/4″ —check your brake calipers for correct size)
  • yellow and blue butt splices
  • wire cutter/stripper/crimper
  • drill & small bits (to put new mounting holes in the floor)
  • clear tubing & bottle for draining brake fluid
  • rags or paper towels
  • headlamp (very useful in small spaces)
  • an assistant for the bleeding process
  • mounting screws
  • screwdrivers
  • a test light or multi-meter
  • wire loom and/or electrical tape

What a great feeling it is to have this done.  Not only are we ready to get back on the road, but I no longer have to worry about a random failure of the brakes. Dexter is a major company with a lot of experience, and they have a good product, so my confidence level in my disc brakes is high—for the first time in years.




  1. marie luhr says

    Rich- you’re not the only one feeling great about your safe brakes! Very sorry about your cancelled trip, though. If I’m right, it was good that it happened at home since you’ve had to wait so long for a new one? That’s my positive spin for the day! I assume you’ll be traveling again soon, what with all that food in the freezer!

  2. Terry says

    The best time for a brake failure is when you are pulling into the driveway after a trip. The second best time is as you are pulling out of the driveway. The worst time is when you are approaching an occupied railroad crossing at the bottom of a very steep hill.