Electric Trailer Brakes. (HELP)

Submitted: Sunday, Jul 04, 2004 at 17:09
ThreadID: 14368 Views:17890 Replies:12 FollowUps:11
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Help required. I have just purchased a Camper trailer and am having some issues with the electric Brakes. I am working with the trailer manufacturer to resolve this issue and yes we are getting there. I think we are just about at the point of replacing the Brake assemblys unless some of you guys can provide a beacon of light. I have documented the symptoms and trouble shooting done below. Please feel free to comment.

Cheers Cruisin

Fault finding done and fault symptoms of 12” Dexter Electric Brakes.


The symptoms below have been found using my Tekonsha Prodigy Brake controller in my own vehicle and also using Wayne’s standard ATS brake controller in his own vehicle

1. Brakes weak and inconsistent, will not lock the rear wheels up. With earlier testing we could sometimes get the wheels to lock up but was not consistent. Recent testing with two separate vehicles and controllers saw that neither vehicle could get any wheel to lock up with the controllers set to maximum..
This applys to both brake assemblys as we cannot lock up either side wheels.

2. Brakes are shuddering/surging when braking slightly harder than normal and in the last 50 metres prior to a complete stop.

As these symptoms where found using two separate vehicles and controllers we can assertain that the problem lies in the Electric Brake assembly or the wiring on the trailer. Wayne has not experienced this shuddering, or not being able to lockup the trailer wheels using his vehicle on any other of his trailers.

Trouble shooting performed.

1. Apon inspection of the trailer, 7 Pin plug, Wayne realised that his builders had used 3mm cable for the brake wires. I have since rewired the Brakes using 6mm Auto Cable. This has made no difference to the performance or symptoms of the brakes.

The following measurements were made using the Tekonsha Prodigy Controller with the output set to Maximum and applying the brakes using the manual lever on the controller.

Voltage measurements using 3mm cable wired to the brakes (Original Wiring)

At 7 pin plug, Pin 3 & 5 13.04 V
At RHS Brake Assembly 12.45 V
At LHS Brake Assembly 12.32 V
No current measurement taken

Voltage measurements using 6mm cable wired to the brakes (Current Wiring)

At 7 pin plug, Pin 3 & 5 13.45V
At RHS Brake Assembly 12.9 V
At LHS Brake Assembly 12.88 V

Current draw of Both Brakes measured at
Pin 5 of the trailer 7 Pin plug. 6.21 A

Current draw of brakes with the 6mm Cable was 6.21 Amps, this is normal for a two brake system.

2. Wayne has removed the Brake hubs and adjusted the brakes to 6 turns out as recommended by his supplier. This also made no difference to the performance of the brakes.

Wayne also inspected both brake assembly and could see no uneven wear on the brakes indicating shuddering or incorrect operation.


As we are seeing the correct voltage and current being applied to the brakes we cannot have an Earthing issue. With this much voltage on the brakes a correctly functioning brake assembly should easily be able to lock up the trailer wheels.
With the shuddering...If the Brake hubs were slightly out of round, this may cause some shuddering but should not stop the wheels from being able to be locked up.
All of this testing has been done with an unladen trailer weighing approximately 800kg.
One must therefore assume that we have a dud batch of Brake assemblys on our hands or a Pair of Magnets that are not operating as they should.
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Reply By: mike - Sunday, Jul 04, 2004 at 18:14

Sunday, Jul 04, 2004 at 18:14
Try backing the brakes off a little at a time, as I have found that this gives the magnet a chance to pick up more momentum & therefor is able to apply the brakes harder. It's worth a try.
AnswerID: 66412

Follow Up By: Member - Cruisin (QLD) - Sunday, Jul 04, 2004 at 18:33

Sunday, Jul 04, 2004 at 18:33
Hi Mike have done all that at many different settings.
Bottom line is I cannot lock the brakes up wherever the dial setting is. This obviously means that I am not getting anywhere near enough stopping power. Remember this is with an unladen trailer. What hope would I have with a laden trailer. The Brakes are 12" electric drums so there should be more than enough grunt to lock them up. The manufacturer reckons also.....Oh yea and then theres the shuddering issue.
These times are meant to try us.
Thanks for the thought though Mike.
Come on you brainwaves out there...I need some help

Cheers Cruisin
FollowupID: 327227

Reply By: mike - Sunday, Jul 04, 2004 at 19:08

Sunday, Jul 04, 2004 at 19:08
Have I missunderstood your reply? What I mean't was to back off the brake shoe adjustment inside of the brake drum to give the magnet more travel before the brake shoes come into contact with the brake drum
AnswerID: 66423

Follow Up By: Member - Cruisin (QLD) - Sunday, Jul 04, 2004 at 19:55

Sunday, Jul 04, 2004 at 19:55
Sorry about that Doug. I thought you were talking about the Voltage applied to the Brake from the Brake Controller
Initially the Camper manufacturer had adjusted the Brake shoes to be 2 full turns of the Star adjuster nut, from locking the wheel. The brake manufacturer was then consulted and he suggested to adjust the brake adjuster 6 turns away from locking the wheel. At 6 turns I can now here the brakes applying and releasing from within the cab. This also has made no noticeable change to braking performance.

Cheers Cruisin
FollowupID: 327235

Reply By: GOB & denny vic member - Sunday, Jul 04, 2004 at 20:15

Sunday, Jul 04, 2004 at 20:15
goodday cruisin
are all the cables terminated properly and not just a couple of strands as the voltages will change under load conditions (power not wieght)if there are only acouple of strands catching .voltage will appear ok until put under load this includes joins under trailer

AnswerID: 66429

Follow Up By: Member - Cruisin (QLD) - Sunday, Jul 04, 2004 at 20:24

Sunday, Jul 04, 2004 at 20:24
I have terminated all cables myself. I am a bit of a nut when it comes to correct cable sizes and terminations. All terminations on the trailer have been soldered e.t.c .
The voltages that I stated in my post are the voltages applied to the brakes under load. There is no voltage going to the brakes when the brakes are not applied. If I am getting 12.9 V at the rear wheels and the brakes are drawing 6.2 Amps, then Ohms Law tells you all connections are working as they should.
But something is still wrong !!!! Frustrating but I will get to the bottom of it.

Thanks for the thought.
FollowupID: 327240

Reply By: AT4WD ADVENTURES - Sunday, Jul 04, 2004 at 21:41

Sunday, Jul 04, 2004 at 21:41
Hey Cruisin,

How have you tested the rig?.....have you tested with a wheel jacked up and hand spun then brakes applied to see if you can get brake lockup? Have you applied 12volt direct to brake magnets as close to source as possible? Does this shuddering occur on both wheels or one?


AnswerID: 66445

Follow Up By: Member - Cruisin (QLD) - Sunday, Jul 04, 2004 at 22:07

Sunday, Jul 04, 2004 at 22:07
All the testing has been done on the road at speeds varying from 10kph and up to 100kph. The test you mentioned about jacking the wheels up then applying the brakes...I have done this and the brake is applied but it would not need much power from the brakes to achieve wheel lock with me only turning it. On the road the brakes do actuate every time and there is breaking force there but it seems there is just not enough of it. I have not applied 12 V direct to the magnets via a battery. But I do see 12.9V right at the brakes and the brakes drawing 6.2 Amps when applied. They say that each Brake should draw approx 3 Amps

Regarding the shuddering, its very hard to tell from which side if not both the shuddering is coming from. At speed I dont have any shuddering its only the last 50Meters or so of braking.

This is where this whole thing is a bit puzzling....As I said earlier I cannot lock up any of the wheels. If I had one side that wont lock then I would obviously look at that wheel but its BOTH ????.
My Brake controller is a new install, but this very camper has been tested on the guys vehicle who builds these campers and tows them around all the time. He knows that his controller is good. Whether its his vehicle or my vehicle towing this thing the camper brakes the same....therefore there must be something crook in the camper !!!

FollowupID: 327253

Reply By: AT4WD ADVENTURES - Sunday, Jul 04, 2004 at 22:34

Sunday, Jul 04, 2004 at 22:34
Hey Cruisin,

The question relating to the wheel jack up was more to determine if the brake magnets do actually work under no load?

I was also looking for you to clear up in my mind if the placement of magnets is correct and will throw the brake shoes even if under no load.

AnswerID: 66455

Follow Up By: Member - Cruisin (QLD) - Sunday, Jul 04, 2004 at 23:01

Sunday, Jul 04, 2004 at 23:01
Hi Stuart

Could you please explain how or why the Brake magnets should work under no load...What does this mean.
I have taken off the Hub and have moved the magnet in the direction of wheel rotation to see if all components are actually working and yes the actuating are expands the Brake pads and all appears visually correct on both sides.

Cheers Cruisin
FollowupID: 327265

Follow Up By: AT4WD ADVENTURES - Sunday, Jul 04, 2004 at 23:07

Sunday, Jul 04, 2004 at 23:07

By no load I mean that the trailer wheel is in the air and spinning by hand and an application of voltage to the brake magnets causes the brake shoes to move against the drum.

This just confirms the correct operation of all components like magnets, springs, levers, shoes etc. of the brake components.


FollowupID: 327266

Reply By: AT4WD ADVENTURES - Sunday, Jul 04, 2004 at 23:11

Sunday, Jul 04, 2004 at 23:11
Continued from above.........................

when voltage is applied to the brake magnets.....this would be my first test.

AnswerID: 66462

Follow Up By: V8troopie - Sunday, Jul 04, 2004 at 23:57

Sunday, Jul 04, 2004 at 23:57
Or it could be something really really stupid - like having the left side brake hub mounted on the right side and vice versa..... worth checking out.

FollowupID: 327272

Reply By: V8troopie - Monday, Jul 05, 2004 at 00:13

Monday, Jul 05, 2004 at 00:13
A further suggestion, wire in an Ampmeter (0-10A) so it can be seen from the driver. I did that with my electric brakes. Tells me instantly if the trailer plug is dirty again, since the poor contact causes a loss of amps in the brake circuit. (manual setting)

Its not the 'voltage' you measure in the circuit, its the actual AMPS flowing through the coil that builds up the magnetic field that works the brakes.
Since the same number of AMPS flow along every point of the circuit, from the controller to the magnet, its easy to see whats going on.
More voltage will give you more Amps, of course, but voltage measurement can be so misleading since it is different at every point along the circuit due to voltage drops.

For your brakes to shudder, caused by an electrical fault, you would see the Ampmeter's needle pulsing madly. If the meter is steady and the brakes shudder you have some mechanical problem within the brake drums (see my suggestion above :-)
AnswerID: 66467

Reply By: Member - Jeffrey - Monday, Jul 05, 2004 at 07:32

Monday, Jul 05, 2004 at 07:32
Hi Cruisin,
I dont know if I can help,but years ago I had a similer problem with drum brakes,on my harley,it would'nt matter how hard you hit the peddle you would keep on sailin down the hwy,my brakes were brand new,reco, new linings,machined for out of round,anyway what I had to do was and I don't know if there the same,was ecentuate the leading and trailing bevel on the shoes and then I had to relese the locking mech on the drum the one that stops the drum from spinning when the brakes are applied ,spin up the wheel by hand lock the brakes up,keep them locked while you tightened up the lock nut,this then centralised the shoe contact with the drum.After that a bug landing on my peddle would lock them up.
Hope this helps
All The Best In Health And Wealth
AnswerID: 66476

Follow Up By: Member - Cruisin (QLD) - Monday, Jul 05, 2004 at 09:37

Monday, Jul 05, 2004 at 09:37
Good thought Jeffrey. Not sure if there is an alignment adjustment on the Brakes but will certainly investigate.

Cheers Cruisin
FollowupID: 327281

Reply By: andysgu - Monday, Jul 05, 2004 at 21:07

Monday, Jul 05, 2004 at 21:07
You didnt mention if it is a new trailer or old .
If old have you had the hubs machined on both surfaces some brake places are only equiped to do one .
Sounds like every thing is working as it should exept the magnet isnt getting enough grip .
Have you got the right magnets ?
l know you have checked the wiring but a poor earth can stuff everything up.
Another silly sugestion is you may need to bed the magnets in .

Good luck

AnswerID: 66584

Follow Up By: Member - Cruisin (QLD) - Monday, Jul 05, 2004 at 22:59

Monday, Jul 05, 2004 at 22:59
Brand new Camper

Cheers Cruisin
FollowupID: 327367

Reply By: AT4WD ADVENTURES - Monday, Jul 05, 2004 at 21:11

Monday, Jul 05, 2004 at 21:11
Hey Cruisin,

How are we doing after all these suggestions.

AnswerID: 66585

Follow Up By: Member - Cruisin (QLD) - Monday, Jul 05, 2004 at 22:58

Monday, Jul 05, 2004 at 22:58
Hi all and thank you for your suggestions.
The trailer is going back to the manufacturer tommorrow and he will investigate further. I think we are getting down to replacing both drums with another new set just to try something new. Its all it can be is something in there !!! I am taking the cruiser down to the manufacturer and will tow one of his other trailers to prove once and for all that my brake controller is Ok...I hope. It happened with the manufacturers truck also so I think I am safe there. Just nice to know and will give me a reference as to what a correctly working trailer should act like.
After all this is a brand new camper so it is the manufacturers responsibility. I have just been working with him as he is as mystified as I am.
Will keep you guys posted and thanks again for the tips.

Cheers Cruisin
FollowupID: 327366

Reply By: Member - Cruisin (QLD) - Tuesday, Jul 06, 2004 at 09:06

Tuesday, Jul 06, 2004 at 09:06
The latest news

I took the camper back down to the manufacturer today and I towed another one of his brand new trailers with my vehicle.... Smooth as silk...no shuddering and I could easily lock up the wheels. It was wonderful compared to how mine is behaving. We now know that my vehicle wiring is alright and that it is a hardware fault with the brakes. Manufacturer rang his Brake distributer and they seem to think that it might be the backing plates, that holds all the shoes and magnets together. They are supplying 2 new backing plates this morning and then they'll be fitted today. Time will tell but we are moving forward. Its nice to know my vehicle is wired Ok....as you always suspect your own work first !!!

Stay tuned
AnswerID: 66633

Follow Up By: Member - Cruisin (QLD) - Tuesday, Jul 06, 2004 at 20:25

Tuesday, Jul 06, 2004 at 20:25
Backing plate means all components except for the drums. If this doesnt work...drums will be replaced.
FollowupID: 327467

Reply By: Member - Cruisin (QLD) - Thursday, Jul 08, 2004 at 22:21

Thursday, Jul 08, 2004 at 22:21
Well its been a battle but the problem has been found.
2 Faulty drums....Brand new from the Dexter factory. Dont know whether they are out of round or what. To look at the drums with the human eye they appeared normal...no uneven wear marks...nothing. Replaced these with another set of drums and they are certainly working well now. Can lock em up no worries with 285x75x16 All Terrains on them. Smooth braking and no shuddering.

Thanks to all who offered suggestions.
Tough nut to crack.

Cheers Cruisin
AnswerID: 67049

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