Advice re caravan electric brake fault

Submitted: Sunday, Sep 08, 2013 at 13:56
ThreadID: 104237 Views:3445 Replies:3 FollowUps:9
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I have a Tekonsha Primus brake controller. I have noticed for some time that applying the brake pedal is ineffective in braking the van [fitted with tandem axles]. To investigate the problem, I jacked the van and rotated the wheels. With the van connected to the car and after adjusting the Power Knob as recommended in the User Manual, I rotated each wheel and operated the Manual Slide Knob to its full extent. The brake on each wheel immediately stopped the rotation. When I operated the brake pedal, it had virtually no effect on any of the 4 brakes on the van. It does not appear to be a matter of brake adjustment.
Does anyone have a suggestion as to what the problem might be?
Alternatively, does anyone have a recommendation re a good automotive/caravan electrician in Alice Springs?
Thanks Guys.
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Reply By: Member - TheFox3305 - Sunday, Sep 08, 2013 at 14:11

Sunday, Sep 08, 2013 at 14:11
Read the owners manual.

The brake pedal does not activate your brake controller. It is inertia controlled, i.e., it is activated by the change in momentum of your vehicle caused by your vehicle's brakes.

The electrical connection to your brakes is for turning on the brake lights when you use the manual slide knob.



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Follow Up By: Member - Lynton B (QLD) - Sunday, Sep 08, 2013 at 14:25

Sunday, Sep 08, 2013 at 14:25
Fox3305: Thank you very much for your very prompt reply. I really appreciated it.
I could be interpreting the manual incorrectly, but it says "The brake control will 'HOLD' your trailer with 25% of power setting while you are at a standstill with brake pedal applied for longer than 5 seconds". In the light of this statement, does your comment still hold?
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FollowupID: 797534

Follow Up By: Member - TheFox3305 - Sunday, Sep 08, 2013 at 14:51

Sunday, Sep 08, 2013 at 14:51
I have the same controller. Never tested that. It may only come on after 5 seconds after normal inertia operation, not how you are trying to test it.

Would be a bit hard to know because the cars brakes would be holding the trailer anyway.

But the only way to test your functions is as per the manual - driving at slow speed and applying the brakes. Do your adjustment as per the manual.

After the adjustment, try one of the boost settings if you like, and that will might show you more of an effect. If you are not used to caravan brakes, you may be looking for a "pull" effect on your car that is not necessarily there. It should assist your braking, not do more than the car. I use my boost settings when going down big hills like Adelaide for a bit of extra confidence.

Most of the time, i cannot "feel" mine working. But when I unplug the controller (or forget to mount it!), I can certainly feel it not working. My van weighs 2.4t empty.
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Follow Up By: Member - Tony H (touring oz) - Sunday, Sep 08, 2013 at 18:56

Sunday, Sep 08, 2013 at 18:56
Hi,
I know with my P3 controller which is an 'inertia' type unit.... it has a critical mounting angle for correct function....bearing in mind Im not familiar with your unit.... but this could be an issue
Insanity doesnt run in my family.... it gallops!

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Follow Up By: Nomadic Navara - Sunday, Sep 08, 2013 at 23:15

Sunday, Sep 08, 2013 at 23:15
Quote "The electrical connection to your brakes is for turning on the brake lights when you use the manual slide knob."

That is erroneous information. That connection is a 2 way connection, it is also used to trigger the operation of the brake unit. When you operate the brake pedal there should be some voltage applied to start the braking effort. When the tugs and the vans brakes start to operate the rig decelerates and the sensor in the Primus detects this and applies more braking effort. The amount of extra effort is proportional to the amount of deceleration.

When the tug is sitting still you should get a voltage reading when you press the brake pedal. You also should be able to see some voltage at the trailer socket on the tug. Check to see what you are getting.

If you are getting voltage at the socket then plug the van in. Check the voltage at the brake magnets (between the two wires at each magnet.) You can also listen for hum at each brake. With the foot on the brake pedal there should be some resistance to wheel rotation.
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Follow Up By: The Bantam - Monday, Sep 09, 2013 at 09:47

Monday, Sep 09, 2013 at 09:47
Things may vary depending on the settings and the controller.

BUT

It may be entirely normal for there to be little or no voltage measured at the magnets and no braking effort with the vehicle stationary and the brake pedal depressed.

If the brake controller is an enertia activated uint.

The brake light switch activates the electronics.....the deceleration sensor ( this may be a pendulum, a ball on a track or something more sofisticated) comes into play.
The vehicle brakes provide the initial deceleration and the trailer brakes follow.

You MUST read the manual for your particular brake controller.

This manual will tell you how to test and set up your brakes.

When manually activated the controller should be able to lock the wheels on the trailer at low speed.

With the older simpler controllers things where realativly simple.

The smarter and more complicated controllers may present chalenges in understanding how they are behaving.

BUT #1, you have proven that the controller can manually activate the brakes.

Step 2 is to check the adjustments of the controller.

If your electric brake system is working well and the rig is set up properly...it should be able to stop you on good flat road so hard you have to decide if you will keep both hands on the wheel or use them to hold ya eyeballs in.

cheers
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Follow Up By: Member - TheFox3305 - Monday, Sep 09, 2013 at 10:10

Monday, Sep 09, 2013 at 10:10
PeterD

I would say you are probably correct about there being some sort of 2 way connection, but I know my controller is functioning and I cannot detect any voltage at my plug as you suggest when the brake is depressed with the vehicle stationary with my Fluke meter.

There is a momentary change on the brake unit display, some voltage may appear for a very short period, but too quick for me to pick up and certainly not constant.

When you are mobile and apply the brakes, the digital display shows the volts being sent out. Not that I watch it all the time, but I rarely see it at or above 7 volts, but it drops off quick as the vehicle slows. Mostly I see 5 volts and below. I suppose there are times when it goes full voltage, but at that point i must be watching what I am about to hit!

My opinion is Lynton's test method is not really proving whether it works or not.
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Follow Up By: The Bantam - Monday, Sep 09, 2013 at 11:51

Monday, Sep 09, 2013 at 11:51
The other thing to remember is that the brake voltage is not constant, it will be a "pulse width modulated" output (series of pulses of varying width and duty cycle), AND it will vary during the braking cycle....the voltage indicator on the control unit will just be a donkey display, to give a vague indication.

As I say at full 12 volts it should lock the wheels.....and possibly at any speed......at full braking effort the pulses have become wide enough that it will be more or less continuous supply voltage.

If you look at the braking capacity of these systems, it would be a very rare situation that any where near full capacity would be required

When set up properly the tow vehicle continues to provide the primary braking effort.

The cycle works something like this.
You apply the brakes in the tow vehicle, the rig begins to slow, the controller detects this deceleration and adds braking effort in the trailer.
If you continue to increse braking effort in the tow vehicle the controller continues to increase braking effort in the trailer.

As you either maintain braking effort in the tow vehicle or back off, the braking effort in the trailer rapidly decreases.

if braking modestly, by the time you come to a stop all the braking effort is in the tow vehicle.

Braking tactics are very important with these systems to get the most out of them.

it is best to.
Bring on the brakes steadily.....this brings the trailer brakes into play smoothly.

Brake harder earlier, bringing on the effort progressivly rather than lighter and later....this brings on best distributed braking effort across the rig and keeping the trailer brakes in operation.

Then feathering off as you come to rest.

"Braking like you mean it" keeps all the brakes in operation and all making a contribution.

Light braking will keep the trailer brakes off more and work the tow vehicle brakes harder.

Stabbing the brakes will not result in smooth braking and good progression in and out of trailer braking.

cheers
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Follow Up By: Nomadic Navara - Tuesday, Sep 10, 2013 at 14:50

Tuesday, Sep 10, 2013 at 14:50
My controller is the Tekonsha P1 which is basically the same as all the others of the current vintage (except for the monitoring functions and displays.) I see some voltage at the socket when foot pedal is pressed. Maybe it's because I use a more suitable meter for the purpose (an analogue one,) or it could be because I use some boost setting.

From FollowUp 6 "I would say you are probably correct about there being some sort of 2 way connection"

Stop being a sore looser and read the literature. That line from the stop light circuit is definitely there to trigger the application of the brakes. If you still don't believe me leave your rig stationary for long enough for the controller to go to sleep. Then press the brake pedal and watch the controller wake up.

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Reply By: MEMBER - Darian, SA - Sunday, Sep 08, 2013 at 16:58

Sunday, Sep 08, 2013 at 16:58
I haven't tried that static function that you describe, but for mine.... I adjust the shoes on all 4 hubs (put on until the wheel can't be turned, then back off until just free)....adjust the Tekonsha Prodigy volts to about 6/7.....leave the boost on 0.....do a mobile test, where I pull the manual lever over fully while free rolling and expect to feel a decent drag from the van .... that's it. While touring, as mentioned above and when braking via the car, the van's contribution may not be noticeable. As for boost, I sometimes run boost in the city, where the need for hard braking can come suddenly. If the above produced nothing for me, I'd be into the electrical side of things.
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Follow Up By: Pelikan - Sunday, Sep 08, 2013 at 17:10

Sunday, Sep 08, 2013 at 17:10
I agree with what Darian said except that I use boost setting number one for a 1300kg single axle camper. The brakes should exert a small amount of braking when you press the brake pedal and you should see the voltage start to register on the display. The inertia sensor increases the braking power in proportion to your decelleration.

Peter H
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FollowupID: 797545

Reply By: Member - DOZER - Monday, Sep 09, 2013 at 06:51

Monday, Sep 09, 2013 at 06:51
check all connections, you will have a bad one somewhere. mine same same, turned out wheel to cable was full of water
b4 you bag me out, walk a mile in my shoes, then your a mile away and have my shoes :)

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