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Caravan Electric Brake Problems Simplified

by | Mar 15, 2020 | Repairs & Maintenance | 0 comments

Caravans and some heavier campers continue to experience braking problems in mountainous regions. Overheating drums are a significant concern for owners as they strive to improve their electric braking.

I am writing from Timaru, New Zealand, where my wife and I stayed with local marriage celebrants Dave and Linda Moore. Friends of the family, Brent, have owned a Jayco for three years in which they have travelled the length and breadth of the southern highlands. However, Brent took the time to note one specific problem to me. “The rear right-hand brake drums get hot when driving down Lindis Pass Range in Central Otago.

Lightly braking the caravan down Lindis Pass still resulted in hot brakes, and checking the brake adjustments did not fix Brent’s problem. The caravan’s setup is tandem axle suspension with Alko 2t drums and 12″ electric backing plates, and evidenced by his story above was experiencing serious caravan electric brake problems.

When he told me of this problem, Brent had no idea I was an ex-electrician working in the caravan industry.

I gave Brent the solution and will show you the secret at the end of this post; firstly, let’s talk about what goes wrong with electric brake components.

Potential Causes of Electric Brake Failure

Electric Magnets

electric brake magnetElectric magnets are formed by winding an insulated copper wire around a plastic bobbin to prevent unravelling. 3mm cables are soldered onto the insulated wire and sleeved. The bobbin is then inserted into a steel holder and encapsulated.

Four dimples are moulded into the encapsulated section. These dimples serve as wear indicators. When a dimple is worn, the magnet needs replacing.

Magnets fail at the point where the wire exits the steel body. It has been my experience that electric magnets are not the cause of braking problems unless they are not working at all.

Magnets cause heat from friction when engaged with the brake drum. This heat is generally generated on one side of the axle when the other side of the axle is not engaging the braking arm.

In other words, the electric magnet has insufficient power to bind to the brake drum.

One electric backing plate (the hot one) breaks the entire axle load instead of two backing plates. For additional information on brake magnets’ issues, check out our Caravan and Trailer Brakes FAQ.

brake magnet arm

Magnet Arm

The electric brake magnet arm is vital in engaging the brake shoes.

  • The bottom metal protrusion holds the magnet. This holding tab is square on the top.
  • The braking arm is located into the backing plate by a centring pin. Note the hole in the arm. This hole elongates when worn and must be replaced.
  • Under the top pivot pin, the square metal section expands and contracts the electric brake shoes once the brake drum moves the arm.
  • A spring forces the magnet to remain square, and a clip holds the magnet into position on the arm.
  • Note: Off-Road magnets have no clip. AL-KO recommends using the rubber band to hold the magnet until the first braking event. The purpose of the rubber band is to stabilise the magnet until the drum is installed and tightened on the axle.

Quality Cabling

Problems with undersized brake cabling are common for all brands of caravans and camper trailers. Ask your auto electrician for voltages at each brake if you suspect a problem. These voltages should be identical or very close.

When purchasing cabling, I recommend buying cable from an electrical store instead of an automotive store. Electrical store cable contains 100% copper instead of automotive stores that could have a mixture of zinc or other alloys in their copper cable. Zinc and other alloys do not conduct electricity as efficiently as copper. This type of cable is also known to create hot joints due to the degradation of the cable material.

Additional information on electric brake wiring is available here.

How can ineffective caravan electric braking be fixed?

A simple fix is to install another strap of cable across the axle. This extra cable reduced voltage loss, thus ensuring full voltage to that lazy magnet.

In my opinion, the whole cable installation should be increased by two sizes of cable. Cables should be run down each chassis rail and not across the axle.

Looking Deeper into Caravan Electric Brake Problems

  1. In an unbalanced system, the last magnet in a wiring loom has the most significant voltage loss.
  2. The voltage loss occurs at the end of the line. The best short-term remedy is to double the size of the wire from one side to the other. Alternatively, you could run an additional supply to the last magnet.
  3. This is tricky because the hot drum is the second last magnet in the wiring setup.
  4. The hot drum is trying to brake the load from the whole axle. Its job is to brake half of the capacity.
  5. The long-term solution is a balanced writing system with cabling of significant size to cater to voltage drops at all magnets.

How to Test?

Measure voltages at each magnet by manually engaging the brake system at the brake controller. Activating the breakaway kit eliminates voltage losses from the in-car brake controller and does not accurately represent total voltage losses.

Where the voltage varies significantly between magnets, upgrade the cable size.

Tekonsha and Redarc tow pro elite are electric brake controllers you can trust. This type of controller is installed in the cab of the tow vehicle.


In rare cases, 10″ and 12″ drums become polarised from constant rubbing by the magnet on the brake drum. Review the post here.

What are the symptoms of polarisation?

  1. No braking.
  2. Braking has gradually become weaker over time.
  3. Replaced the entire backing plate and upgraded cabling with no improvement in the braking problem.


  1. Inspect the inside of the brake drum. If the magnet attachment area is scoured, then replace the drum. You can purchase new Couplemate brake drums here.
  2. If the drum magnet area is ok, reverse the cabling connections. The connections produce either the North Pole or the South Pole on the drum face.
  3. If the magnet and drum face is polarised, a braking event will cause the drums and magnet to repel each other.
  4. Transposing cables reverse the replying event into an attraction event.
  5. Your brakes will return to normal by transposing the wires, provided the drum is polarised.

Finally, a common cause of intermediate brake failure is connecting the negative cable to the caravan’s chassis. Connecting the neutral or the negative line directly into the plug has resolved many braking issues.


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