Caravan Electric Brake Problems





Caravan Electric Brake Problems

Caravans and some heavier campers are continuing to experience braking problems in mountainous regions. Overheating drums are a significant concern for owners as they strive to improve their 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, own a Jayco caravan that they have owned for three years. "It a beautiful caravan and one I have travelled the length and breadth of the southern highlands. Our next trip is the North Island again, once I get over this cold."

There is one thing; however, that is a slight problem. The rear right-hand brake drums get hot when driving down "Lindis Pass Range in Central Otago". This link takes you to the beautifully rugged Southern HIghlands in NZ.

Brents setup is tandem axle suspension with Alko 2t drums and 12" electric backing plates. Brent has serious caravan electric brake problems.

Brent had no idea I was a Master Craftsman electrical when he told me of this problem. 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.

Editors Note: Problems with undersized brake cabling is a common problem across all brands of caravans. If you suspect there is a problem, ask your auto electrician for voltages at each brake. These should be identical or very close.

Contact the experts at Couplemate or our author, Steve Wotherspoon,  if you are experiencing unexplained electric braking problems.

Electric Magnets

electric brake magnetElectric magnets are formed by winding an insulated copper wire around a plastic bobbin and tied off 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 mould 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 baking plate (the hot one) is braking the entire load of the axle instead of two backing plates.

How can lousy 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.

Yes, the smaller cable was installed by the factory, and the factory is a famous brand.

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.

Magnet Arm

The electric brake magnet arm performs a vital role 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.
  • The square metal section under the top pivot pin 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: Offroad magnets have no clip, Alko recommends using the rubber band to hold the magnet in place 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.

Let's return to Brents Problem

Brent has problems with an overheating brake on the right-hand side but only when driving down a mountain pass.

The rig has 12" electric backing plates with 2t Alko Drums.

A caravan mechanic has looked over the drums and correctly adjusted the brakes and bearings.

Looking Deeper into Caravan Electric Brake Problems

  1. The last magnet in a wiring loom has the most significant voltage loss in an unbalanced system.
  2. The voltage loss occurs at the end of the line. Therefore the best short term remedy is to double the size of the wire from one side to the other or 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 1/2 the capacity.
  5. The long term solution is a balanced writing system that has cabling of significant size to cater to voltage drops at all magnets.

How to test

Measure voltages at all magnets by manually engaging the brakes at the brake controller.

Activating the breakaway kit eliminates voltage losses from the in-car brake controller and does not give an accurate representation of total voltage losses.

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

Quality Cabling

When purchasing cabling, I recommend buying cable from an Electrical Store as opposed to an Automotive store.

Electrical store cable contains 100% copper as opposed to 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 degradation of the cable material.

Polarisation

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

[embed]https://youtu.be/Q8rqpSLdNhw[/embed]

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.

Solutions

  1. Inspect the inside of the brake drum. If the magnet attachment area is scoured, then replace the drum.
  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 magnet and drum face is polarised, then a braking event will cause drums and magnet to repel each other.
  4. Transposing cables reverses the replying event into an attraction event.
  5. Your brakes will return to normal by transposing the wires provided the drum is polarised.

Finally, Debbie and I enjoyed the Southern Highlands of NZ so much we will be back to enjoy the other half at some point. Thank you, Brent, it was a pleasure to meet you, and I hope my advice fixes the electrical problem you have endured for such a long time.

 

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