[corksil]

We all know that drum brakes are a very archaic mechanism and they have been around for many years without any changes to the design.

With that said, I'm trying to diagnose and fix electric drum brakes. Electric drum brakes are basically normal drum brakes, with the addition of an electromagnet on a lever which causes the shoes to widen within the drum and create friction which slows the rotation of the axle.

The amount of voltage sent to the electromagnet corresponds to the sticking force of the magnet within the drum, which translates to the outward force applied to the shoes. In simple terms, 1 volt causes brake to barely engage. A full 12 volts causes the brake to engage with the maximum amount of stopping force capable.

I am not able to get these brakes to lock up the axle and cause the tires to skid. I need these brakes to fully lock up the axle as a matter of safety. If the brakes cannot fully stop the rotation of the axle, they are deemed unsafe because the stopping force required to slow the load will be solely the responsibility of the tow vehicle. The combination of trailer [with weak brakes] behind tow vehicle with inadequate braking system to stop the tow vehicle AND trailer could result in all sorts of horrendous things which I would rather not get into.

I have already re-wired the entire braking system of trailer and replaced most of the truck wiring between dash-mounted brake electric brake controller and the trailer connection plug at back of vehicle [power for lights/brakes/turn-signals.]

I'm getting 10 volts at the magnets on the trailer brakes. The brake controller is putting out 12.5 volts at the back of the truck. I don't believe the voltage drop is due to insufficient wire size because I re-wired the braking electrical circuit entirely with 12awg wire and the trailer manufacturer used 14awg when the trailer was built.

The brakes USED TO lock up both trailer axles but they have become weaker over time. I need to fix this issue.

Any ideas?