caravan brakes

Submitted: Friday, May 17, 2013 at 19:19
ThreadID: 102269 Views:1894 Replies:7 FollowUps:6
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Hi I used to tow my 16ft van with a magna and had no problems now I have a Nissan navara and cannot get proper brakes, I have tried 2 different brake controls and have 13.5 volts at the plug and have put in new magnets but still have to have the brake controller turned up flat out to get brakes and virtually no brakes on the emergency slide, there is 12 volts at the wheels, and the brakes are adjusted properply any ideas Graeme A.
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Reply By: Michael ( Moss Vale NSW) - Friday, May 17, 2013 at 19:55

Friday, May 17, 2013 at 19:55
Graeme, run an earth out of the seven pin socket on the Navara to a bolt on the bulbar. If you have the gear, you could drill and tap a new hole for the new earth. You should already have a good earth from the chassis to the bull bar. Generally earthing is the problem. Its normal to have the voltage at 13.5 but is can drop if the earth is bad when load is applied. The problem is normally the earth , or earth or the earth! I hope this helps. regards Michael
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Follow Up By: Michael ( Moss Vale NSW) - Friday, May 17, 2013 at 23:11

Friday, May 17, 2013 at 23:11
Oops I meant tow bar, not bull bar! Michael.
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Reply By: Member - Keith P (NSW) - Friday, May 17, 2013 at 19:55

Friday, May 17, 2013 at 19:55
It is really hard to diagnose these sorts of issues from here....but the first thing that jumped into my mind was.."check the earths...." at both wheels ...and from trailer to tow vehicle thru the plug.

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Follow Up By: kookaburra - Friday, May 17, 2013 at 20:12

Friday, May 17, 2013 at 20:12
Id get another Magna,
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Reply By: rocky279 h - Friday, May 17, 2013 at 20:37

Friday, May 17, 2013 at 20:37
Over-Run brake systems are fitted to all caravans in the UK and all trailers that are rated above 750Kg weight capacity. So what are over-run brakes?

When you apply the brakes in your towing vehicle, there has to be some way in applying the brakes on the trailer or caravan you are towing. The brakes on a lorry trailer are activated by compressed air. Obviously this system cannot usually be fitted to cars (some Land Rovers can have an air system for towing) so a different solution was sought. As the possible combination of tow vehicle to trailer or caravan was huge, a simple system that required no modification to the tow vehicle was sought. The over-run system was originally called the ‘surge brake’ when it was developed.
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AnswerID: 511268

Reply By: Ross M - Saturday, May 18, 2013 at 00:06

Saturday, May 18, 2013 at 00:06
Beside the blue brake wire in pin 5 in the towbar 7pin socket , the earth wire should also be connected to the chassis and or battery negative or both for preference.

Appropriately, the power from the controller must go to the magnets AND also return to the plug earth. It seems this isn't happening due to poor connections or incorrect wiring.

Something I have seen is,
instead of the brake power and earth wires being Y connected therefore evenly distributing the controllers energy to both brake magnets, someone had connected the brake magnet coils in series instead of parallel. This effectively halved the power through each magnet and although they sort of worked they were ineffective, even when the controller was turned up full.
Has any work been done on your van's brakes since the Magna towed it?
Best to keep humans away from things that are working, if possible.

Ross M
AnswerID: 511287

Follow Up By: Ross M - Saturday, May 18, 2013 at 10:34

Saturday, May 18, 2013 at 10:34
The brake magnets have a resistance of around 3.0 ohms and two of them in parallel as is normal, should then read (along with the wiring) around 1.7 ohms at the plug if tested with a multimeter at pins 2 & 5.
If not close to this there is a problem.

Also another quick test is to use a battery supply 12v and briefly touch the trailer plug pins 2 and 5. The amps current flow should be about 7 amps. DO NOT DO THIS FOR VERY LONG only briefly. You will require an ampmeter for this measurement. Some multimeters will test this amount of flow safely.

Ross M
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Follow Up By: Ross M - Saturday, May 18, 2013 at 10:40

Saturday, May 18, 2013 at 10:40
SPECIAL NOTICE
MAKE THAT pins 3 AND 5 NOT 2 and 5

Why aren't we able to EDIT? EDIT? EDIT? EDIT? EDIT? Am I repeating myself?
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FollowupID: 789491

Follow Up By: Member - J&R - Saturday, May 18, 2013 at 13:44

Saturday, May 18, 2013 at 13:44
No need to connect the earth wire to both the battery negative and the chassis 'for preference'.
In all cars made in the last 20 years they are one and the same.

But the silliest thing to do is to run earths, for such things as auxilliary batteries, Anderson plugs almost anwhere, or for accessories back to the battery. You're doubling voltage drop. The battery is earthed at the chassis and the engine, usually both in the engine bay. The return of lowest resistance is the chassis.
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FollowupID: 789505

Reply By: steved58 - Saturday, May 18, 2013 at 16:30

Saturday, May 18, 2013 at 16:30
Is the wiring to the plug on the towbar of the correct size undersize wiring can cause insufficient braking check your controller instructions for reccomened minimum wiring size
Good luck steve
AnswerID: 511317

Reply By: graham B9 - Saturday, May 18, 2013 at 19:28

Saturday, May 18, 2013 at 19:28
I think what you are saying is that you are towing a different caravan to the one you had with the Magna.

You did not say what brand of van but I suspect that there is just one wire that running to all brakes. There sould be a seperate set of wires to each brake and then eathered at the brake. This wire should come from the plug where it is connected to the tow vehcile. I would check the wiring.
AnswerID: 511332

Follow Up By: Ross M - Saturday, May 18, 2013 at 21:36

Saturday, May 18, 2013 at 21:36
You can't earth the magnets at the brakes, if it is a leaf spring there is no connection to the chassis. All you might have a flapping cable for the hand brake and that isn't what anyone would call an earth connection.

There has to be a wire back to the plug for earthing and then to the vehicle chassis/battery negative.
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FollowupID: 789554

Reply By: Nomadic Navara - Saturday, May 18, 2013 at 23:44

Saturday, May 18, 2013 at 23:44
You say you have 12 V at the wheels. This should be only at one wire going into the magnets. The other wire should be at or near 0.0 V with reference to the chassis.

We have had situations on forums where the van that has had brake problems has had both wires to the magnets connected to the active wire. This is not your problem is it?

If the two magnet wires are not connected together but you have 12 V on both wires it means you have an earthing problem through your trailer connection as suggested above.
PeterD
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AnswerID: 511350

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