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Brakes?


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#1 meddyliol

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Posted 04 November 2010 - 12:04 PM

This is probably a stupid question but how do the brakes work on a caravan? What actually pulls them on?

Cheers

Brian

#2 philspot

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Posted 04 November 2010 - 12:15 PM

When your car slows, the caravan "overruns", its weight pushes it forwards and compresses the black "concertina" which covers the shaft that holds the towhitch. The shaft then pushes via a pivot and pulls the rod which runs all the way under your caravan to the axle. There, the pull is split to both side brakes via cables. These cables pull the brake shoes into contact with the drums. The caravan slows. This means the shaft that was pushed back will now move forward again, so releasing the brakes. And so on and on...
The shaft is damped to avoid all this turning into a bouncing contest.
More details from others, I'm sure.

#3 rustygates

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Posted 04 November 2010 - 12:26 PM

Hi Bri,

To keep it simple for you, the caravan brakes are called overrun brakes,they are mechanical and not hydraulic and rather basic. As you apply the tow vehicle brakes the weight of the van pushes forward the moving part of the hitch which in turn pulls the rod that is attached centrally to bowden cables which are attached to the brake shoes which then open up forcing the brake shoes against the brake drum and they are very efficient if adjusted properly and the handbrake pulls the same rod to apply brakes when stationary.

This is how I see it working, their maybe some on here that see it working different, we shall see.

rustygates.

#4 RogerL

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Posted 04 November 2010 - 01:30 PM

More details from others, I'm sure.

Not necessary - that's concise and straightforward.

#5 Gordon

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Posted 04 November 2010 - 01:51 PM

Spot on descriptions above. The only thing I would add is that most caravans now have auto-reverse brakes. That is to say that the "overrun" brakes disengage when the caravan is reversed. In response to a reverse rotation of the caravan wheels, the brake shoes are withdrawn from contact with the brake drum, as the operating mechanism "collapses" within the brake drum, such that compression of the drawbar does not operate the brakes, and prevent the caravan from moving. Normal operation is automatically restored as soon as the drawbar is extended, and the caravan moves forward again. This is also the reason why you should always fully apply the handbrake lever to the upright position. This action compresses a spring, and the energy stored is used to overcome the collapsed brake mechanism, and apply the brakes should the caravan try to run backwards when unhitched!

A bit of history:
On very early models this operation was manual, and the brakes had to be disengaged by operating a locking mechanism on the drawbar. On the earliest models this also had to be reset manually, and could easily be overlooked, resulting in a caravan with no operational brakes, even when towing forwards. However on later models the brakes were automatically reset as soon as the caravan was moved forward, so the caravan brakes could not be left not working, but this could be inconvenient if the outfit had to be manoeuvered back and forth several times, as the brakes had to be turned off again avery time the outfit was reversed.

Gordon.

#6 CommanderDave

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Posted 04 November 2010 - 02:14 PM

A bit of history:
On very early models this operation was manual, and the brakes had to be disengaged by operating a locking mechanism on the drawbar. On the earliest models this also had to be reset manually, and could easily be overlooked, resulting in a caravan with no operational brakes, even when towing forwards. However on later models the brakes were automatically reset as soon as the caravan was moved forward, so the caravan brakes could not be left not working, but this could be inconvenient if the outfit had to be manoeuvered back and forth several times, as the brakes had to be turned off again avery time the outfit was reversed.
Gordon.

Those were the days before bellows when you had to jump out and push a curved half round flap over the draw bar to stop the drawbar compressing and pushing the brake lever as you say you soon found out when you tried to stop that it was still on now we take auto reverse for granted .
Dave

#7 Gordon

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Posted 04 November 2010 - 02:34 PM

Those were the days before bellows when you had to jump out and push a curved half round flap over the draw bar to stop the drawbar compressing and pushing the brake lever as you say you soon found out when you tried to stop that it was still on now we take auto reverse for granted .
Dave

How right you are Dave! Happy days (Not)
Attached File  VintageTowhitch.jpg   23.99KB   12 downloads

#8 bigjimmy

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Posted 04 November 2010 - 05:17 PM

As the caravans are so damned expensive and as motor technology has moved on so very far, I just wish that caravan and trailer brakes had moved on a quantum leap more so as to keep pace.

But hey ho who are we to ask for better mechanical equipment..............................and by the way Gordon, CommanderDave and others, some excellent explanations on the way they work.

#9 BrianI

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Posted 04 November 2010 - 05:29 PM

See here
http://www.al-ko.co....g-operation.htm
Brian

#10 Cruzer

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Posted 04 November 2010 - 05:29 PM

As the caravans are so damned expensive and as motor technology has moved on so very far, I just wish that caravan and trailer brakes had moved on a quantum leap more so as to keep pace.

If they had caravans would be even more damned expensive than they already are. There are some benefits to good old technology.




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