On this page (6 sections)
Electric drum brakes and why they fade
An electric drum brake works by sending current to an electromagnet that drags against the rotating drum face. That drag pulls a lever, which spreads the shoes against the drum. Braking force is therefore proportional to current, which is why a brake controller output setting matters and why a bad connection anywhere in the circuit reduces braking rather than eliminating it. This is a system that degrades quietly instead of failing outright, and that is what makes it dangerous.
Magnets wear as a normal consequence of operation. The friction face gradually thins and the coil eventually shorts or opens, and a magnet that has worn unevenly will also score the drum face it rides on. Measuring magnet thickness and checking coil resistance against specification takes minutes per wheel and tells you exactly where you are. Replacing magnets in pairs across an axle keeps braking balanced, which matters more on a trailer than on a car because the driver has no pedal feedback to warn them.
Shoe and drum condition follows the same logic. Drums wear oval and develop a ridge at the outer edge, and shoes glaze from heat or contaminate from a leaking grease seal. A contaminated shoe cannot be cleaned back to usefulness and replacing one on a single wheel puts uneven force across the axle. Self-adjusters seize with rust on units that spend most of their life parked, so shoes that have never adjusted keep working with an ever-larger gap and less and less braking.
The wiring is the part nobody looks at. Trailer brake circuits run the length of the frame, ground through the frame at each brake, and terminate in a seven-way connector that lives behind the tow vehicle in road spray. Corroded pins, a chafed run over a frame flange, and a poor ground are the three most common causes of weak or one-sided braking, and all three read as bad brakes to the person feeling it from the driver seat. We measure current at each magnet with the controller commanding full output, which finds the fault immediately.
Electric over hydraulic and disc conversions
Heavier fifth wheels and toy haulers increasingly use an electric over hydraulic actuator, a Dexter DX series or Carlisle Hydrastar unit, which takes the electric signal from the controller and uses it to drive a hydraulic pump feeding conventional wheel cylinders or calipers. It gives smooth proportional braking and far more capacity than drum magnets can produce. It also introduces hydraulic fluid, bleeding procedures, and an accumulator to the maintenance picture.
Actuator faults usually announce themselves through a warning light or an audible pump that runs continuously. A pump that cycles when no braking is commanded is losing pressure somewhere, and the usual suspects are a caliper seal, a line fitting at a frame crossing, or the actuator internal check. Fluid condition matters too: brake fluid is hygroscopic, it absorbs moisture over years, and a trailer that sits for long periods accumulates water that lowers the boiling point and corrodes bores from the inside.
Disc conversions are a worthwhile upgrade on heavy units and they are not a bolt-on. The hubs, rotors, calipers, and actuator have to be matched as a system, the wheels must clear the caliper, and the controller has to be one that outputs a signal the actuator understands. Done properly the result is braking that does not fade on a long descent and that requires almost no periodic adjustment. Done as a parts-bin exercise it produces a trailer that brakes worse than the drums it replaced.
Bearings, seals, and the truth about grease fittings
A trailer wheel bearing is a tapered roller set, typically an inner and outer cone and cup with a grease seal behind them, and it fails from contamination and from heat rather than from mileage alone. Water intrusion past a tired seal emulsifies the grease and etches the rollers, and the resulting roughness generates heat that thins the remaining grease and accelerates the whole process. The end of that story is a seized bearing, a spindle welded to a hub, and a wheel that departs the vehicle.
Inspection means disassembly. Cones come out, everything gets solvent cleaned, and the rollers, cages, and cup races get examined for pitting, spalling, and heat discoloration. Cups that are marked get driven out and replaced along with their cones as a set, because mixing an old race with a new cone gives you the wear pattern of the old race immediately. Spindle condition matters as much: a scored or blued spindle from a previous failure will not support a new bearing for long.
The grease fitting in the end of an EZ Lube style spindle is genuinely useful and it is also the most misused feature on any trailer. Grease pumped in with the wheel stationary, or pumped too fast, pushes past the rear seal and straight onto the brake shoes, which contaminates them permanently. The correct procedure is to rotate the wheel while pumping slowly and to stop as soon as clean grease appears. A great many brake jobs we do exist because someone greased a hub the wrong way.
Reassembly is where torque specification earns its keep. Bearings are seated by rotating the hub while tightening to a preload figure, then backed off and set to a light running clearance and secured. Too tight generates heat and destroys a new bearing in a few hundred miles. Too loose lets the cone hammer in the race. Doing this by feel is common practice in this trade and it is the reason so many bearings fail early.
Axles, hubs, and the hardware that holds the wheel on
Dexter and Lippert supply most of the axles under North American towables, and both build in a slight upward camber so that the beam deflects to straight under load. An axle that has been overloaded, or that has struck something hard, loses that camber permanently and the tire then rides on one edge with the tread crowned in the wrong direction. Straightening is possible on some beams and inadvisable on others, and we say which applies after measuring rather than promising a cheap outcome.
Hub and spindle damage from a bearing failure usually means replacement rather than repair. Where the spindle has scored, the axle has to come apart or come out, and on some designs the spindle can be cut and welded rather than replacing the whole beam. Whether that is the right call depends on the axle rating and how much life is left elsewhere in the assembly, and it is a decision we make with the customer rather than for them.
Wheel attachment hardware is the last item and it deserves more respect than it gets. Lug nuts on trailer wheels must be torqued in a star pattern to specification and then retorqued after roughly fifty miles, because the wheel seats slightly against the hub face under initial use. Missing that retorque is the leading cause of wheels working loose, elongating the stud holes, and eventually shearing studs. We retorque before delivery and we tell owners to do it again once they are on the road.
What is included
- Magnet and shoe measurement
- Friction face thickness, coil resistance, and drum condition checked at every wheel against published specification.
- Brake circuit current test
- Current measured at each magnet with the controller at full output, which finds a corroded pin or a bad ground immediately.
- Full bearing service
- Disassembly, solvent clean, race and roller inspection, new seals, and preload set to a torque specification.
- Hydraulic actuator service
- Pressure and cycle behavior verified, lines and calipers checked, and hygroscopic fluid flushed on units that sit.
- Axle and spindle assessment
- Camber measured, spindle condition evaluated, and a straighten, replace, or re-spindle recommendation given with reasoning.
- Wheel hardware and retorque
- Studs and stud holes inspected, lugs torqued in a star pattern, and the follow-up retorque interval explained.
Signs you need this work
- The tow vehicle does nearly all the stopping and the trailer feels like it is pushing
- A squeal or grinding from one wheel that changes when you apply the brakes
- One wheel hub noticeably hotter than the others after an hour of driving
- Grease slung across the inside of a wheel or streaked on the fender
- A brake controller that reports a short or an open circuit intermittently
- The trailer pulling to one side under braking
Frequently Asked Questions
How often do trailer bearings need repacking?
Annually or roughly every twelve thousand miles is the accepted interval, and sooner for anything launched into water or driven on salted roads. It is not really about mileage. It is about seal condition and moisture, and a trailer that sits nine months a year in a coastal climate can accumulate water in a hub without turning a wheel. Storage does not pause the clock on this one.
Why does my trailer barely brake at all?
On an electric system, braking force follows current, so weak braking usually means the circuit is not delivering it. Corroded seven-way pins, a chafed frame run, a poor ground at one backing plate, or a controller set too low all produce this. Worn magnets and out-of-adjustment shoes do too. Measuring current at each magnet separates a five dollar connector problem from a full brake job in about twenty minutes.
Is a disc brake conversion worth doing?
On a heavy fifth wheel or a toy hauler that sees mountain grades, yes. Discs do not fade the way drums do on a long descent, they self-adjust, and they need far less periodic attention. The cost is real and the system has to be matched end to end, including an actuator and a compatible controller. On a light single axle trailer used locally, well maintained drums are perfectly adequate.
Can you tell if my axle is bent without special equipment?
Often, yes. A bent beam shows up in tire wear pattern, in measured camber at the hub faces, and in the clearance from tire to fender compared side to side. Confirming it takes measurement from fixed reference points rather than a look. Where the beam has lost its built-in camber from an overload, tire wear will tell you long before anything else does.
I greased my hubs and now the brakes barely work. What happened?
Grease almost certainly pushed past the rear seal onto the shoes. It happens when the wheel is not rotating during greasing or when the grease goes in faster than the cavity can accept. Contaminated friction material cannot be cleaned or burned off in any lasting way. The repair is new shoes, a new seal, and a cleaned drum, and the correct greasing procedure demonstrated so it does not repeat.
Do you service brakes on motorhomes as well as trailers?
On gas and diesel motorhome chassis we handle what falls inside our licensed scope, and for anything in the chassis brake and drivetrain system on a commercial truck we refer out. Towable brakes, axles, hubs, and bearings are fully in house, including tandem and triple axle setups. Call and describe the unit and we will tell you which side of that line it lands on.
Related services
- Leveling and Suspension
Hydraulic and electric leveling, air bags, and ride height correction.
- Frame and Structural Repair
Frame straightening, chassis alignment, and welded structural repair.