The short version
- The bearing work is identical. The brake assembly is what makes it a longer job.
- On drums the backing plate and shoes stay behind while the hub comes off.
- Grease and brake friction surfaces must never meet, and this is where they usually do.
- Electric brakes add a magnet and wiring. Hydraulic surge brakes add a line you should not disturb.
Repacking trailer wheel bearings with brakes fitted is the same bearing job with an assembly in the way. The complications are predictable.
None of them are difficult. All of them are easier if you know they are coming.
Which system you have
| Setup | What is behind the hub | Main complication |
|---|---|---|
| No brakes | Nothing | None, hub slides straight off |
| Electric drum | Backing plate, shoes, magnet, wiring | Magnet lead, shoe adjustment |
| Hydraulic surge drum | Backing plate, shoes, wheel cylinder | Hydraulic line, do not disturb |
| Hydraulic surge disc | Caliper over a rotor | Caliper must come off first |
Drums are the common case on road trailers. Discs are increasingly usual on boat trailers, because they shed water better.
The drum sequence
On trailer wheel bearings with brakes of the drum type, the drum and hub are usually one casting. The hub carries the friction surface with it.
- Chock, jack and support the trailer properly, then remove the wheel.
- Back off the brake adjuster if the drum will not clear the shoes. There is usually a slot in the backing plate.
- Remove the dust cap, cotter pin, castle nut and washer as on any tapered hub.
- Rock the hub so the outer cone drops into your hand, then slide the hub and drum off together.
- Leave the backing plate alone. The shoes, magnet and wiring stay on the axle.
Worn shoes wear a lip into the drum, and the drum then catches on the shoes on the way out.
Slacken the adjuster before fighting it. Levering a drum off against tight shoes damages both.
The rule that matters most
You are handling packed grease inches from brake shoes and a drum. Contaminated linings cannot be cleaned, only replaced.
Wear gloves, change them before touching the brake side, and keep the packed cones in a clean container until they go in.
Grease on a lining is not a cosmetic problem. It costs that brake most of its effectiveness and it is not recoverable.
The same reasoning is why overfilling a hub matters, as the grease quantity page covers.
Electric brakes specifically
Two things to watch, and both are easy to get wrong once.
The magnet lead. It runs through the backing plate and it is not long. Pulling the hub off without noticing can stretch or break it.
The magnet face. It rubs against the machined face inside the drum. Any grease on that face means the brake will not grip properly.
Inspect the magnet while everything is apart. A worn or scored one is far easier to change now than later.
Hydraulic brakes specifically
Drum or disc, the guidance is the same on one point.
Do not open the hydraulic line. Removing a hub does not require it, and disconnecting means bleeding the system afterward.
On disc setups the caliper comes off and gets supported so its weight does not hang on the flexible hose. A cable tie or a hook is enough.
A caliper left dangling puts its full weight on the hose, which damages it internally without any visible sign.
That failure shows up later as a brake that drags or will not release.
Extra checks while it is apart
The hub being off is the only convenient time for several inspections.
Shoe or pad thickness, and whether wear is even across both sides.
The drum or rotor surface for scoring, cracks or heat discoloration.
The magnet on electric brakes, for wear and for a scored face.
The wheel cylinder on hydraulic drums, for any sign of fluid seeping past the rubber boots.
The spindle itself, which is on the trailer replacement page.
Boat trailers with disc brakes
Worth a separate note because immersion changes the priorities.
Discs handle repeated dunking better than drums. Water drains off a rotor rather than sitting inside a drum.
The bearing side is unchanged though. Water still gets past seals as a hot hub cools in cold water, and that is what sets the service interval.
Why immersions rather than miles decide the schedule is on the trailer section, and pressurized caps are on the dust cap page.
Putting it back
Refitting trailer wheel bearings with brakes follows the standard procedure, with one addition.
Readjust the brakes after the hub is back on and the nut is set. Drums that were slackened to get the hub off will not brake properly until they are reset.
Then test at low speed before towing anything. The adjustment sequence for the bearings is on the repacking guide.
Common questions
How do you repack trailer wheel bearings with brakes?
The bearing work is unchanged. Back off the brake adjuster so the drum clears the shoes, take the hub and drum off together, and leave the backing plate on the axle.
Why will the drum not come off?
Usually the shoes are holding it, because wear has cut a lip into the drum. Slacken the adjuster through the slot in the backing plate.
What is the biggest risk?
Grease reaching the brake linings. Contaminated shoes or pads cannot be cleaned and have to be replaced.
What is different about electric brakes?
A magnet lead runs through the backing plate and is short enough to damage, and the magnet face inside the drum must stay free of grease.
Do I need to open the hydraulic line?
No. Removing a hub does not require it, and disconnecting means bleeding the system afterward.
What should I check while it is apart?
Shoe or pad thickness, the drum or rotor surface, the magnet on electric brakes, the wheel cylinder, and the spindle.
Anything to do afterward?
Readjust the brakes once the hub is back on, then test at low speed before towing.