Member Since: 13 Oct 2014
Location: Nottingham
Posts: 1788
Learned something new and had a relatively lucky escape
Did you know, if you unhitch your caravan on an uphill slope with the handbrake applied, but with tension on the hitch, it operates the rollover brake and starts running down the hill when the tension suddenly releases. Neither did I until today.
Fortunately the curb angled in after about 15 feet, so the only damage was a neighbour's fence, a bit of a wall and a cracked window and panel on the back of my tintent.
Scared me s tless though, dragging me along as I desperately tried to release the overrun and reapply the handbrake. Lots of cars down the road it could have run into, and nobody about to injure so it could have been far worse.There are two rules for success,
1. Never tell everything you know.
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25th Apr 2017 7:41 pm
Russell
Member Since: 23 Aug 2007
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Heard that before but not sure I would remeberMY17 D5 1st Edition Namib Orange
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25th Apr 2017 8:02 pm
rrhool
Member Since: 28 Aug 2014
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Never unhitch with the car uphill. My twin axle trailer is the same, the auto reverse brakes are so sensitive, it will run backwards with no trouble, even with the hand brake full on. Richard
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25th Apr 2017 9:02 pm
Gareth Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26779
I didn't know this, but I thought that was to reason that the hand brake lever is sprung? On my current caravan (Elddis Affinity) the brake handle is Spring assisted, so once I lift the lever it applies itself. I unhitch all the time on a sloping drive (no choice), and as the van comes free from the car, it does roll back a bit, but as it does, the handbrake lever moves further into engagement, to a vertical position, and the van stops.
My previous van (Fleetwood) the handbrake had to be pulled on, but also had a spring which I had pull the lever until it had stretched the spring. Again, as the van came free, the Spring in the brake lever put the brakes on despite the overrun on the shoes.
So car uphill, van / trailer is lower down the hill, how is the auto reverse brake override system kicking in?
Think I'm lost here, surely the hitch is fully extended at this position, I.e in the towing position not in the reverse position that overrides the braking Altox GSM FBH controller thread
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25th Apr 2017 9:47 pm
Gareth Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
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In an uphill situation, before you unhitch the trailer or caravan, apply the hand brake. OP is saying that the reverse over-ride is releasing the brake and allowing the caravan to continue to roll backwards.
I thought that the hand brake had a spring that is supposed to overcome the reverse over-ride.
In normal manoeuvres such as reversing the trailer, the over-run hitch initially applies the brakes, but the shoes are designed to slip backwards on the brake backplate, and down a cam, to release them.
I might be wrong because I'm no expert, but I reckon there could be an adjustment issue.
I have the bad habit of engaging the motor mover before I try to unhitch as it is handy to shoogle the coupling to persuade it to release.A vaccine does not stop you catching a virus, or passing it on, or getting ill from it, really ill. It does reduce the likelyhood of you dying when really, really ill. Stay Alive - KEEP AWAY FROM PEOPLE.
25th Apr 2017 11:08 pm
Madrilleno
Member Since: 13 Oct 2014
Location: Nottingham
Posts: 1788
I *think* that a combination of factors caused the problem.
1. Hitch was under tension when handbrake was applied
2. On auto reverse hitches, the brakes do not apply until up to 10" of rear wards travel
3. My road has a significant slope, meaning that a significant amount of kinetic energy was gained in the 10" of travel
4. The release of the tension on the hitch reduced the tension on the handbrake allowing a further increase in speed
5. At this point the caravan brakes operated as though the vehicle was being reversed and the autoreverse mechanism was triggered
6. The caravan handbrake is not designed to function as a dynamic brake. Yes, it can be used as one, but it is not designed to cope with significant reverse speeds. Once the reverse mechanism has operated, you basically have no brakes at all until tension in a forward direction is applied, allowing the auto reverse mechanism to reset.
I will be following Navigator's method in future, and applying my motor mover before unhitching.
PARKING
The handbrake, in conjunction with the energy store, is used to apply the brakes when the trailer is parked.
As the handbrake lever is raised, its lower end makes contact with the lower end of the overrun lever and begins to apply tension to the brake linkage.
As the handbrake is raised further the energy store mechanism moves overcentre and pulls the brakes on fully. The spring energy store is pre-tensioned with a force corresponding to at least the actuating force applied during normal trailer braking.
If the trailer is rolling rearwards as the handbrake is applied, or if it is pushed backwards with the handbrake on, the autoreverse mechanism will be brought into action.
To overcome this, a greater actuating movement is introduced from the spring energy store, expanding the brake shoes further so that full brake effectiveness is maintained.
There are two rules for success,
1. Never tell everything you know.
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26th Apr 2017 5:49 am
Robbie
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Seems like madness in the design if it can move with the handbrake applied. An accident in such circumstances is foreseeable, opening up a path of litigation.Land Rover - Turning Drivers into Mechanics Since 1948
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I always leave the safety cable attached until I've completely unhitched on our horsebox. at least then, if it starts to roll the handbrake should apply before it gets too far..
Might be good practice to fit a chock when on a slope? hope you get all the damage sorted in house and you have forgiving neighbours Disco4 MY16 SDV6 Landmark Black
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26th Apr 2017 8:06 am
B16 KJR
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Brilliant thread and I've certainly learnt something today..... will treat trailer brakes with a bit more attention in the future!
Thanks Madrilleno for highlighting the issues!
26th Apr 2017 11:53 am
Madrilleno
Member Since: 13 Oct 2014
Location: Nottingham
Posts: 1788
Browny90 wrote:
I always leave the safety cable attached until I've completely unhitched on our horsebox. at least then, if it starts to roll the handbrake should apply before it gets too far..
Might be good practice to fit a chock when on a slope? hope you get all the damage sorted in house and you have forgiving neighbours
This time I was lucky, and the lesson is now well ingrained. I'm also lucky to have good neighbours who were far more concerned for my welfare than that of their fence.There are two rules for success,
1. Never tell everything you know.
I always leave the safety cable attached until I've completely unhitched on our horsebox. at least then, if it starts to roll the handbrake should apply before it gets too far..
Err - no!
That is the point of this thread. A trailer will roll backwards in certain circumstances EVEN WITH THE HAND BRAKE APPLIED. All that will happen in your scenario is that the breakaway cable will snap as well.A vaccine does not stop you catching a virus, or passing it on, or getting ill from it, really ill. It does reduce the likelyhood of you dying when really, really ill. Stay Alive - KEEP AWAY FROM PEOPLE.
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tless though, dragging me along as I desperately tried to release the overrun and reapply the handbrake. Lots of cars down the road it could have run into, and nobody about to injure so it could have been far worse.
