Thursday, August 19, 2010

That's the Brakes

No, it's not a misspelling, just a poor pun in the title, but you will understand why after reading this post.

As I mentioned in the previous post, we are having new brakes put on the trailer.  A little background is in order.  Most RV trailer brakes are electric.  It is a system that has been around for many, many years.  It consists of drum style brakes on each trailer wheel that are engaged when an electrical current activates an electromagnet that tries to grab the turning wheel drum.  This in turn causes the arm attached to the electromagnet to turn, thereby mechanically applying the brake shoes through a gear and cam system.  The electric current is supplied from a brake controller on the tow vehicle.  This controller can be of various types but is most commonly a mechanical or electronic pendulum that senses when the tow vehicle is slowing, and applies a proportionate current to the trailer brakes.

There are many problems with this type of system, but one benefit.  It is cheap.  That's why trailer manufacturers use them.   The drawbacks are that they need constant adjustment, do not work well when hot, are not proportionate to the brake pedal pressure, tend to rust when not used, rely on electrical signals and a lot of wire that is exposed to the elements and passes through fuses and connectors, including the notoriously unreliable trailer plug where the lights also connect.  Although there are better brake controllers for the tow vehicle, they do not address most of the issues.

All cars use hydraulic brakes, and have since the 30's or 40's.  Hydraulic brakes use a couple cylinders and brake fluid that presses the brake shoes or discs against the braking surface.  Starting in the 60's disc brakes also replaced drum brakes on the front wheels of most cars (where most of the braking occurs), and now many cars have disc brakes on front and rear.

RV manufacturers have continued to use electric brakes, and do to this day.  In recent years however, some aftermarket manufacturers as well as some axle manufacturers have begun offering hydraulic disc brakes for RV's.  It is rare for them to be offered on new trailers except as an option on the heaviest or custom rigs, but many owners are now upgrading their rigs with the newer systems.  The resulting improvement in braking performance is remarkable.

There is still the decision about how to apply the brakes.  Disc brakes need hydraulic pressure and use brake fluid.  It is not possible or practical to tie into the tow vehicles braking system, and of course it is impossible when the tow vehicle has air brakes like we do.  The two basic approaches are to use an electrically operated hydraulic pump that is controlled by the same old inertial brake controller, or if you have a tow vehicle with  air brakes, use the air system to operate a hydraulic master cylinder, very similar to the way it happens in your car.

The advantage of the air actuated system is obvious.  There are no electrical connections to corrode, short out or fail.  The system relies on the same air pressure from the truck to apply the trailer brakes as it uses to apply the truck brakes.  The brake response is instantaneous (unlike the electrical type that must wait for the hydraulic pump to spool up) and proportionate.  The system is installed in the trailer and consists of an air tank, a master cylinder and a few valves.  Air is provided through the use of the same "glad hands" that all commercial trucks use to supply air to their trailers.  Those are the red and blue coiled air hoses you see connecting the truck to the trailer.

All those who have had this system installed rave about it.  It is a tremendous improvement in safety and driveability.  We are looking forward to reporting on our experience with it as soon as we get it installed.   And therein lies the rub, so to speak.  Although the brake controller system arrived from the manufacturer as promised, and is already installed on the truck and trailer, the disc brake manufacturer had supply issues and did not ship them until last Friday.  They are expected to arrive on Wednesday and should be installed Thursday and maybe into Friday.

So here we sit, hiding behind a building in an industrial park.  We do have 50 amp electric and water hookups, and we have internet and TV, so other than the view it's not too bad.  We'll let you know how it all turns out.

Update --

The parts arrived on Wed as scheduled and today was install day. Well, almost. Some of the parts were the wrong ones, so the correct ones have been ordered but will not be here until Monday. So we get to spend another weekend in the industrial park. It could be worse. I could be paying to park here.

Maybe we will take a ride on the scooter this weekend to see some more of NH.


  1. I admit I skimmed over some of the technical jargon in this post.

    I remember Dad had a little lever under the steering wheel for the brakes on our first trailer. In my mind's eye, I can see him pulling that lever to the right when stopping the rig. It sure swayed, though.

  2. I keep checking to see if you've put up anymore pictures but nothing new since Western NY. Didn't you take any pics in Boston?

  3. I read every word (well, I skipped one of the "the's" in the second paragraph, but I read all the rest), and it was interesting. I'm glad you didn't leave anything out -- I learned a lot.

    Interested to hear how the new brakes work.