Potential Causes for Overheating Trailer Brake Drums

Updated 09/12/2017 | Published 09/10/2017

Question:

If the disconnect brake battery is bad could that cause overheating all four hubs get hot

asked by: Lee C

Expert Reply:

Trailer breakaway batteries are usually rated for 5-amp-hours and are designed to keep your four brake assemblies engaged for 15-minutes in the event of an accidental disconnect.

The only way the breakaway battery could heat up your drums is if it kept the brakes engaged as you drove. In the same way, if there were a short in the vehicle or trailer wiring that somehow let your 12V power feed reach the brake circuit, which would also keep the brakes engaged. Either way you would probably feel the drag from the trailer brakes as you drove.

If it happened that all four of your brake magnets went bad at the same time (unlikely) then that input power could heat up the magnets and even if the trailer were still there would be some waste heat build-up in the drums from the energized magnets.

I would more expect your issue to be from a mechanical problem than from the breakaway battery. For instance, if you recently greased your bearings and accidentally over-tightened the hub castle nuts this could lead to heat in the drums. If there is insufficient grease in the hubs, if one of the bearings has become damaged or if the magnet is damaged and is dragging on the drum surface these too could cause heat build up.

I suggest you pull at least one of the hubs to check for any signs of mechanical damage, a short in the brake magnet wiring or any other issue that would allow continuous friction to generate the heat you're finding. You can refer to the linked article for help on testing the magnets themselves by using a voltmeter like # PT89ZR.

expert reply by: Adam R