Electric brakes

Maybe a bit on how they work...IMHO

The shoes are 'leveraged' onto the drum

'Leveraged' from the arm connected to the pivot at one end and the
magnet at the other end

The magnet slides on the drum center (AKA spider, plate). It is smooth
and the mating face of the magnet is liewise smooth

When the brake controller sends voltage to the magnet...it grabs the
smooth surface of the drum's plate

As it 'grabs' the surface...the rotating tire/wheel/drum moves the
lever arm...that then pivots the other end of that lever to push the
shoes outwards

That then touches the drum braking surface to create heat by scrubbing
the friction material against it

The 'reach' of the shoe is limited and as the friction material wears...
it needs to be adjusted via the star wheel...which moves the shoe
closer to the drum.

The self adjuster, star wheel, is supposted ot auto adjust, but they
normally don't work well enough. So manually adjusting the star
wheel is the norm



Electrically...there is a relationship between voltage and current
(amperage).

The size/condition of the feed wires...to the wires coming out
of the magnets makes up the 'fed' circuit. If the wires are too small
or frayed, etc...it can NOT deliver enough amperage...even while it
may deliver full voltage under no or very light load (like spinning
it by hand)



Good controllers will have self diagnostic circuitry to tell you if
it thinks there is something wrong



The OP can learn if they havfe the proper manuals, tools and someone
who knows enough to teach...but this is a huge safety area and suggest
having a certified ASE Brake mechanic review the situatioun

You are correct that full voltage does not mean correctly adjusted brakes. Also, the fact that you cannot turn the wheel when the breakaway lanyard is pulled does not mean you have correctly adjusted brakes.

If you lift the axles, spin one wheel without any electricity applied and if it spins easily then the brakes need adjusting. Turn the star wheel via the slot in the rear of the drum until you cannot turn the wheel. Then back it off until there is a slight drag on the wheel. That wheel is now done and you can do the next.

We have a very good tutorial on the forum about adjusting brakes and repacking wheel bearings that is complete with pictures here. It should give you a lot of help. :)
Barney

Need help understanding the following:

Can brake shoes still be loose even though each shoe is receiving full voltage? Seems to me that full voltage is good but does not ensure correctly adjusted brakes.

Does not being able to turn the wheel when elevated mean that the shoe is adjusted properly? I tried that once-could not turn the shoe but rig was not stopping properly with all 4 brakes. No grease or oil on shoes.

Jack one side of the trailer to raise the wheels off the ground, then pull the break-a-way switch, now try to turn the wheels. If you can turn the wheel, you either have a brake problem or a blown seal and grease in the brakes. Do the same for the other side of the trailer. This method won't tell you if they're adjusted properly, but will tell you if they are functional.

This is the spec (I hope is correct) and is the only way to tell if up to spec

Just hearing it does not tell if up to spec

Get an amp meter to read the current (average)

K Charles wrote:
7 inch Diameter Brake Drum
Max Amps at 9-10.5 Volts Max Amps at 12-13 Volts
2 Brakes 4.7-5.6 6.3-6.8
4 Brakes 9.5-11 12.6-13.7
6 Brakes 14.3-16 19.0-20.6

10 and 12 Inch Brake Drums
Max Amps at 9-10.5 Volts Max Amps at 12-13 Volts
2 Brakes 5.6-6.6 7.5-8.2
4 Brakes 11.3-13.3 15.0-16.3
6 Brakes 17.0-20.0 22.6-24.5

jmtandem wrote:
In many cases it can be as simple as having somebody listen to the magnet while another person steps on the brake.

This, it's really that simple. If you can hear the magnet buzz then it's working. You can also put your hand on the wheel and feel a high frequency buzz.

I have done two things in my days, buying new and used trailers.

1. Manually activate the brakes to 100% via the brake controller when connected to the tow vehicle. Make sure each wheel with brakes locks up. This can be done from a stand still, or very slow speed in a parking lot.

2. Pull the emergency break away switch and pull with the TV. This checks the on board battery, and each brake at each wheel, to be sure they lock up.

Via my the above testing, I found one wheel not braking due to a loose wire on a brand new TT. And I found on an almost purchased used trailer, the break away switch not only had a broken wire, but also the small on board battery was junk. Zero voltage.

Moved from Forum Technical Support

^^ do this on both sides of the trailer

You can also put a compass near the drum to sense the change in the EM field.

In many cases it can be as simple as having somebody listen to the magnet while another person steps on the brake.