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Discussion Starter #1
Hi friends.

As usual i am with odd question: does anyone know how much power ( HP or kW ) average vacuum pump fitted to diesel cars is using. I am trying to figure out is it viable to fit 12v electric DC motor to a vacuum pump sourced from , lets say diesel laguna mk1. I am trying to supply brake servo with vacuum.
 

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Once sufficient vacuum is created it will not be under load so the energy saving when braking will be very little. Only when more vacuum is required will it need to work harder and during that time you will be braking anyway.
 

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Discussion Starter #3
What i am trying to do is to be able to use full strength of brakes while towing vehicle with a-frame fitted with brakes.
My thinking was to use such combination in order to comply with trailer ( as A-frame + car is recognised) brake strength regulations.

Cheers
 

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The effectiveness of the brakes is not determined by how much vacuum there is but by the overall effciency of the cars braking system.

The power gained form a servo is finite and is governed by the atmospheric pressure available on the surface of its diaphram.
 

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Discussion Starter #5
I know that. Let me paraphrase the question:

What size 12v dc motor will be sufficient to supply vacuum to servo so that brakes dont go hard after a couple of times pushing on the pedal. Ideally it would be running of reinforced stop light signal for trailer light board, so that vacuum pump would be running only when brakes are pressed on the towing vehicle.
 

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Discussion Starter #6
Anyone?

Just want your opinions.

Will i have to have car starter motor size dc motor or decent 12v battery drill dc motor will do the job.

Other ideas:

windscreen wipers dc motor
electric windows dc motor
radiator fan dc motor
internal blower motor
or
winch dc motor ( ouch- expensive )
 

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Discussion Starter #7
Now i just had another idea-
What if i was to modify Secondary Air Injection Pump from vauxhall vectra 1.8 year 1998 (I happen to have one - its couple hundreds miles away at the moment).

So i am considering 2 options:

reversing polarity on the dc motor, but i believe its centrifuge type of pump, so it wouldn't make much difference.

Than other idea is to modify its inlet.

Any ideas regarding this subject or am I on the right track?
 

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Technical Supremo, Platinum Member
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What about on of those electric pumps for blowing up and emptying inflatable boats and air beds? although I still don't get why you would want to.
Are you trying to fit servo brakes to your A frame? or to have the brakes of the vehicle on the A frame help with the braking?
The trailer I tow as brakes quite capable of momentarily locking the wheels on the trailer in a emergency stop.
 

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Why bother with another pump - diesel vacuum pumps run continiously anyway.

Why not fit air air cylinder to store more vacuum,

Either way you'll be restricted by the capacity of the servo. What you have to remember about vacuum servos is that they ain't powered by the amount of vacuum but by natural air pressure.

If the brakes currently cannot cope then either there is something amiss or the car is being used beyond its capacity which in itself is dangerous.
 

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Discussion Starter #10
I think you didn't get the idea.
I am going to tow a car with a-frame long distance.

Car that will be towed is classified as trailer over 750kg and has to have brakes.

My a-frame has attachment that uses overrun type hitch to push brake pedal in the car that is towed.

BUT what happens with pedal after you depress brakes 2-3 times without running the engine? - they become hard and useless.

I cant have that as I am going to tow like that internationally.

So in order to have brake pedal always soft I need to supply vacuum to the servo of a towed car while its engine is not running.
 

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Technical Supremo, Platinum Member
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Ah I get it now
 

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Yes know I see what is meant.

Obviously the car being towed will have to be braked and also modified to suit whatever type of fixed A-frame system is being used.

If I remember correctly such systems need to have type approval and introducing another addition to the method of braking is likely to mean the approval certificate would no longer be valid.

In the interests of safety I think the question originally asked may be better directed to the company who supplies the A-frame kit.

It may also be prudent to find out if such systems are legal in the countries to which you intend to travel.:)
 

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Discussion Starter #13
Its all gray area as most people outside Uk haven't seen a-frames like that. :d

So... with a copy of UK law about them I should be OK.
 

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There are a number of issues involved when towing a car with an A-frame.

There seems to be plenty of discussions on the mortorhome forums. I have read through a few of them and as yet I have found no definitve answer regarding the legal aspects in European countries. IT would seem the Spanish police tend to take a dim view.

Have a search of the web for motorhome sites and forums. Her's ome to get you started.

http://www.wildcamping.co.uk/forums...base/7508-frame-towing-definitive-answer.html
 
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