If the trailer brakes can be manually pushed but don’t lock under pull, chances are
they have a MECHANICAL issue that needs addressing. There are various things you
can try in order to isolate the source.
One way of checking voltage output from a 7-pin plug connector is to attach a
voltmeter in series with its power wire. You should see up to 12V here.
Brake Shoes
RV’s that use electric brakes must be regularly inspected and serviced for best
performance, however issues may occasionally arise that necessitate further
troubleshooting to determine why its brakes are not functioning correctly.
An electric trailer generally uses electromagnets that attach themselves to a
spinning drum to apply friction, then displace shoes away from it via lever arm
displacers to achieve braking. Current is supplied through a brake controller
connected to the trailer battery.
Sometimes removing the cover, cap or plug from a brake chamber requires
dismantling it and using an adjustment tool such as a brake spoon (or flathead
screwdriver) to turn the adjuster wheel in it manually. Even self-adjusted brakes
need periodic manual intervention if components begin wearing out over time.
Brake Pads
Symptoms If your brakes don’t lock when they should when instructed by the
controller, there could be an issue with their shoes or pads. Worn out brake
shoes/pads can’t apply enough pressure to engage break magnets to start up your
braking system and thus stop working correctly.
Electrical connections within a trailer plug may become corroded or blocked with
dirt over time, and using WD-40 to spray over them should help clear away any
foreign elements and improve the connection. You could also disconnect and
reconnect it three to four times to see if that helps further.
Another potential cause is a bad ground wire. If the main vehicle ground and brake
magnet ground wire aren’t attached correctly to clean metal surfaces, this can
reduce brake system voltage significantly and result in low brake system voltage. An
ammeter can help identify whether there is any potential grounding issue with your wiring.
Brake Pedal
Many trailers feature a mechanical pin which prevents the surge actuator from
compressing & building pressure when in reverse mode, which could prevent your
brakes from engaging when pulling forward. If this pin remains inserted when driving forward it could prevent your brakes from engaging when needed.
Checking this can be done either with a voltmeter or by simply looking. When
connected with the break away system active and the brake magnets connected to
full truck voltage (depending on your controller gain settings).
If the wheels turn when depressed, this indicates a mechanical issue which must be
rectified by disassembling both wheels & drums and inspecting both shoes & drums
for worn linings or scoring; raising and crawling underneath with special brake
adjustment tool as required to inspect shoes & drums thoroughly for wear linings or
scoring; this process should preferably be handled by a certified professional if
towing over rough terrains is involved.
Brake Controller
An electric brake controller that fails to power trailer electromagnets could be due to
wiring issues or defects. A voltmeter can help identify system voltage by connecting
to any of the lead wires of any of the brakes; for best results, do this while your
vehicle’s engine is running so a low battery won’t adversely affect readings; initially
it should start out at zero volts and gradually increase up to 12 as you activate magnet bars.
Test whether your red wire is connected correctly by having someone push the
manual override button on the controller. This bypasses the red wire and powers
your brakes directly; most modern brake controllers are proportional and respond
directly to any changes in brake pressure of a towing vehicle; older time-delay
controllers typically function using predetermined capacity settings and time delays;
proportional controllers offer more versatility since they adapt automatically as
conditions change over time.