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msar-riders - Re: [MSAR] Trailer one brake locking up

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  • From: "IRVIN LICHTENSTEIN" <ilichten1@verizon.net>
  • To: "'Mounted search and rescue'" <msar-riders@lists.ibiblio.org>
  • Subject: Re: [MSAR] Trailer one brake locking up
  • Date: Sun, 15 Apr 2012 21:48:57 -0500

The usual problem with electric brakes is not coming on due to a broken
circuit.
Assuming the wiring is not feeding just one wheel the rest of the system is
a mechanical drum brake. It depends on a magnet to move the leading edge of
the shoe against the drum which then pulls in the rest of the shoe. They are
retracted by springs. There is an adjuster on each set of shoes that can be
manually set to handle wear on each set of shoes. Normally, when my trailer
is inspected they pull the wheel and drum together by taking the bearing
retainer nut off so they can check the shoes and bearings at the same time.

First step is to jack the trailer up and hand spin the wheels/tires. They
should turn easily but not spin real easily. Then apply 12VDC to the breaks
by unplugging them from the tow vehicle and then pull the breakaway. If the
battery is good (or use another 12VDC source) the wheels should not turn
easily or at all (brakes are on).
Third test is restore the breakaway and pull the wheels. The drums should
be removable by hand (if the trailer has been sitting a few mallet taps may
be needed). Look at the bad wheel and a good one for comparison. The tight
brake may be excessively adjusted in or the other 3 might be out too much.

In the past any problem I have had has been in the wiring -- bad grounds
stopping a brake from coming on or a bad connecter letting the 12VDC utility
line leak across to the brakes, locking all 4. Once the battery charger for
the breakaway shorted out. It is rare for a foreign object to get into a
drum brake system because the drums cover the system.
If it was a short activating it, the brake would be on all the time the
power was on. Most likely it is a bad adjuster or springs letting the shoes

get out of line and hang up.

Depending on the tow vehicle the brake lights may control the trailer brakes
or the controller is plugged into the anti-lock system on most GMC/Chevy's
and Ford's. It is very unlikely that a controller could hang a single brake
as it powers all 4 from a common source and to a common wire back to the
trailer. This is true even if you get brake pulse from the hazard warning
lights.

-----Original Message-----
From: msar-riders-bounces@lists.ibiblio.org
[mailto:msar-riders-bounces@lists.ibiblio.org] On Behalf Of Una Smith
Sent: Sunday, April 15, 2012 1:42 PM
To: msar-riders@lists.ibiblio.org
Subject: [MSAR] Trailer one brake locking up

Not MSAR relevant except that it concerns readiness for safe emergency
response.

This is a dual axle trailer with electric brakes that hasn't been used
for months (winter) and now is not 100%. One brake is locking up at
the slightest touch of the brake pedal that actuates the brake lights.
Could this be a wiring fault? Or could some object be embedded in the
brake pad? Or?

Anyone have relevant experience?

Una Smith
New Mexico
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