Electric brake advice?

[sundvl76]

I recently purchased a 4-year-old horse trailer and in checking it out front to back, discovered that one of the brake drums has severely overheated at some time in the past. There was apparently continuing problems with this brake, too, because the previous owner had just installed 4 brand new tires a month before I bought it, and the tire where the overheated drum is located shows obvious signs of having been locked-up and dragged (flat spots).

I've taken the drum off but see no obvious problems with the brake mechanism and the shoes were not adjusted too tight - the drum came off fairly easily. The shoes expand and retract OK by hand, so I don't see any hang-ups or frozen connections.

Could the electro-magnet be at fault? Seems fairly simple - either it is energized or not energized, but maybe the windings are messed up so they cause a stronger magnetic attraction?

Any experience with this from any of you?

Thanks,
Neal

[chandler]

It could be the servo is locking up unexpectedly. With that said, the opposite brake set up may be too loose, and is not engaging at all. I would pull that side as well to see what is up on it.

[retired wrench]

This could be the only one working. Apply the brakes and put something metal near the magnets and see if it grabs it.

[sundvl76]

Good suggestions - I had not considered either possibility, so I will check them both out.

Thanks!
Neal

[retlaw]

step1 check and adjust any free play in wheel bearings. or better still remove wheels and bearings and replace all bearings packing with the correct grease reassemble and adjust bearings.
2.check to see if all brakes are working ,they will normally hum when in operation standing still. make sure each brake is applying by turning each wheel when jacked up.
3.adjust brakes on each wheel.
4.road test and you may feel it dragging on one side but not always, but if a brake is locking on it will be hotter use caution feel brake drum.
5.other things to look for, correct brake shoes and springs ect. correct instalation and there is more but you may have a fix by now

[sundvl76]

Retlaw, thanks for the input. I pulled both left side drums and found that the rear one had blown a grease seal, which of course ruined the shoes. Purchased and installed a pre-assembled backing plate with shoes, springs and magnet. Repacked both left-side bearings with new seals. I also re-did the wiring connections where the main harness connects to the left-side brakes. Jumpers from the left-side drums feed the right-side drums.

Right side bearings seem adjusted correctly - no movement in the wheels as you would find if bearings were too loose.

Adjusted all brakes identically, and test drove. Now both fronts work well, but both rears are weak, even with new shoes and magnet on the left side. Fronts will lock up on gravel with controller turned to max, but rears will not. Wheels off ground, I find the rears are engaging, but I can still force the wheels to turn by hand. Not so with fronts.

Main harness is 14 ga. wire, wire to right side brakes is 16 ga. One might think this contributes to the problem, but as I found, the right front works well.

Still scratching my head. . .