Troubleshooting Electric Drum Brakes Not Stopping Trailer Despite Voltage at Brake

Question:

I am having trouble with my electric brakes on my 2011 keystone sprinter. They are not stopping trailer even when I use the manual over-ride. I can drive down the street and push the override and the truck is not affected. I tested the voltage coming out of the truck at the 7 way connector and am getting 13v. I tested the wire coming into the electric brakes and am only getting 9.5 v. I figured even with 9.5 v I should get some breaking? I took off one wheel and bearing and the magnet was becoming magnetized when I pushed the manual overide. The plug coming from the trailer is pulling away a bit, exposing some of the wires, I was going to replace this as well. Are the trailer brakes just in need of replacement? I am not sure where to go from here.

asked by: John M

Expert Reply:

Thank you for the photo of your Sprinter's 7-way plug and the details of your trailer brake troubleshooting efforts. Both are helpful.

Your issue with the trailer's brakes not slowing the trailer (despite getting 9.5 volts of power at the brake) is most likely related to their pad pressure needing adjustment but since you also have exposed wiring on your 7-way this too should be addressed. If it is not a problem now it could be in the future. Water can migrate into the molded connector and cause internal corrosion that might be tough to spot. You can use part # HS381-9000 to replace yours. This kit includes the molded plug and a junction box for making your connections to the trailer's wiring.

The 9.5 volts you're reading at the brake is not enough power to lock up the brake but it is enough for it to engage and put drag on the drum. This is why I suspect the issue is pad pressure.

Your brakes have a star wheel adjuster for pad pressure. This can be rotated with a spoon tool # W80630 or flat-blade screwdriver. Rotating the wheel upward increases pad pressure. When adjusted correctly you should hear and feel slight drag on the drum as you rotate the tire by hand.

expert reply by: Adam R