Note On A-Frames

Discussion in 'Motorhome Chat' started by 45eEver, Apr 15, 2009.

  1. 45eEver

    45eEver Read Only Funster

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    Well, I've been all through the A-Frame stuff, and I can't find a solution to the need for auto-reverse brakes that I added to the DfT stuff.

    [FONT=&quot]Any braked trailers manufactured after April 1989[/FONT] :Sad:[FONT=&quot]must be fitted with a auto reverse brakes[/FONT]:Sad:[FONT=&quot] to give braking efficiencies required by EEC Directive 71/320 (ECE13).[/FONT]

    Anyone got a solution to the apparent need for auto-reverse brakes on an A-Frame towed car please?

    Yes, I read the bit about a fine every so often being better than a trailer, I can readily go along with that, but so I daresay has my insurance company.
    I prefer not to give my insurance company a cop-out clause.

    I only sell trailers when I no longer have a use for them Jim.
    If I no longer need my Carcaddy, I'll let you know.
    A Carcaddy is a folding break-back trailer that will carry a medium sized saloon car, and fit in an average lock-up garage, and yes, I'd much prefer an A-Frame like I used in the old days.
     
    Last edited: Apr 15, 2009
  2. davejen

    davejen Funster

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    Hi, I tow a Smart with my m/h on a Towtal A frame. The brake pedal is connected by a cable to the hitch so when you brake in the m/h the brakes ion the Smart come on as well. Hope this helps
    Dave:thumb:
    o
     
  3. 45eEver

    45eEver Read Only Funster

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    Thank you for your reply Dave.

    Auto reverse brakes aren't exactly what it says on the box.
    With typical British expertise, whichever officials invented the name didn't understand what they were on about, and gave them a nonsense name.

    "Auto reverse brakes" automatically DON'T work when you reverse.
    As you can probably imagine, they don't fit them to cars.

    In the old days, we had to go round the back of the car and put a metal flap in the way to stop trailer brakes working when we backed.
    Otherwise we just pushed the trailer back with it's wheels locked, or stalled the engine.
    Inevitably we left the flap down when we drove off after reversing and caused accidents.
    That system became illegal on NEW trailers years ago.

    Incidentally, and I'm assuming you have vacuum servo-assistance on the brakes on your Smart Car, do you run an airline from your tow vehicle vacuum to your Smart Car vacuum Dave?
    To comply with your insurance company rules, you need (assuming you have vacuum brakes) to have a vacuum in your Smart Car vacuum system when you tow it.
    Otherwise, it's brakes won't meet efficiency standards, and your ins. co. can void your insurance.
    Another way to get the brakes on your Smart Car legal is to use an electric vacuum pump to suck air out of it's brakes.
    Unfortunately, I don't know the number of the EU directive that controls such a mods though.

    Oh, if you go/went the electric pump route, you need to run the vac pump off the tow car's electricity to avoid a flat battery on your Smart Car.
     
  4. Geo

    Geo Trader - Funster

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    This subject has been covered before and I conducted a few tests on our Mot brake rollers in response to that post
    Brake efficiency is NOT effected by the lack of, or failure of power or vacuum assistance :thumb:
    Geo
     
  5. 45eEver

    45eEver Read Only Funster

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    That's very astonishing Geo, that you found that a vacuum servo doesn't increase brake efficiency.
    How do you explain it please, it seems illogical?

    How did you simulate over-run braking on the coupling when you had the car/trailer on your MOT rollers please?

    My '40s car romps through the MOT brake test with a servo fitted, whereas it just about scraped through before I fitted the servo.

    Does your A-Frame only work the handbrake by any chance?

    Incidentally, since the DfT have included the caution about maintaining servo assistance in their note, which do you consider as more likely, that an insurance company would take the DfT's word, or that they would have independant tests conducted?
     
  6. davejen

    davejen Funster

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    I don't think a servo makes the brakes MORE efficient, but that it makes it EASIER for us weaklings to push the pedal! I will defer to Geo on this one though.
    Dave:thumb: ps the weight of the toad and inertia will put the brakes on on braking.
     
    Last edited: Apr 16, 2009
  7. 45eEver

    45eEver Read Only Funster

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    I went along with what the DfT said when I used the term efficient Dave.
    If I would have used the term more powerful of my own bat.

    I tend to agree with you along the lines that a vacuum servo makes brakes easier to apply.
    I can also agree along the lines that a brake servo makes brakes more powerful.

    Another advantage to a brake servo is that it allows manufacturers to use shorter brake pedal arms, and hence shorter pedal movement.
    Us weaklings use the brake pedal as a lever rather than push directly on the mastercylinder piston.

    Anyway, how does your A-frame apply the footbrake please Dave?
     
  8. Geo

    Geo Trader - Funster

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    Motor vehicles of various types were tested both with and without engine running ie with and without servo assistance
    in all cases the same readings were achieved, it is not possible to simulate over run on a brake roller
    Your 40s car will have had drum brakes all round and drums are more efficiant than disc brakes they proberbly reqd more effort to achive a satisfactory reading due to that paticular system's ineficianies.you would not get higher readings just by fitting a servo,just less effort to get what you got
    The Dft would have great difficulty in saying that the vehicle had poor braking because the servo was not working, if so how did it get type aproval:Eeek:
    When you think about it, all accidents are atributable to lack of braking power servo or not:Rofl1::Rofl1::Rofl1:
    I use an American Brake Buddy with my A frame:thumb:
    Geo
     
  9. davejen

    davejen Funster

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    Hi, 45eever, as I said in my post it is connected via a cable to the coupling head with a lever, so when you brake in the m/h the overrun effect pulls the cable and hence the brake pedal in the Smart. Asthe Smart weighs in at about 900kg you are getting that force on the pedal, so probably as much or even more than prssing the pedal with the servo working.
    Dave:thumb:
     
  10. 45eEver

    45eEver Read Only Funster

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    Thanks for that info about your experiments Geo.
    I'll try replicating them when I get my old nail tested next.

    The authorities seem to have double standards about cars on A-frames.
    On one hand, they say they are trailers, on the other hand, if the car isn't taxed, MOT'd, and insured, they reckon you can't take it on the road.
    I assume the DfT's statement about needing a working servo stems from the second view.

    Am I correct that a car fails it's MOT if it's servo isn't working please Geo?

    I assume the BrakeBuddy works off an intertia switch, am I correct please?
    Does reversing cut the BrakeBuddy out of the system please?
    Has the BrakeBuddy got Eu approval yet please?
     
  11. pappajohn

    pappajohn Funster Life Member

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    i beleive there are two types of brakebuddy.....
    the cheaper one works off the vans brakelight switch and is not proportional.....brakes either on or off, so if you brake very gently, as long as the brake lights are lit, the toad brakes will be fully applied regardless.
    by my reckoning...not a good idea as the toad will be braking for the van.

    the more expensive ones use a potentiometer to apply the toad brakes with the same progressive effort as the vans brake pedal exerts.

    reversing with a brake buddy is not an issue as there is no mechanical (rod or steel wire)link to auto-apply the brakes.

    i doubt very much if they will ever get type approval as electric brakes, as a sole means of braking, are not permitted. (as far as im aware at least. i did read it somewhere on a gov website)

    as for the servo and MOT.....i would say if the minimum efficiency is reached then its a pass.
     
    Last edited: Apr 16, 2009
  12. Geo

    Geo Trader - Funster

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    Its a good job this didn't appear in the quiz John:Rofl1::Rofl1:
    I'm not aware of a Buddy that works like your descriptions mine certainly doesn't. we weren't talking MoT and servo, but if we were, it does matter considerably, even if the efficiancy is met, it fails if the servo is inoperative:Doh:
    Geo
     
  13. pappajohn

    pappajohn Funster Life Member

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    taken from post #10

    Am I correct that a car fails it's MOT if it's servo isn't working please Geo?

    i bow to your superior knowledge as an MOT tester Geo.

    as for the other comment........ya know yer right:Blush: brains still at lochness......i was thinking about electric brakes on a 5er.:Doh:
     
  14. Geo

    Geo Trader - Funster

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    I see where you went wrong John
    I was answering the one above the one below at the side of the one you thought i was answering at which point we wernt talking mots till you brought it up in the one following the other that was not read till after that Just for clarity im repyling to post 10 now:Rofl1::Rofl1::Rofl1:
    Hi45e
    you arrnt half causing some confusion:Rofl1:

    Am I correct that a car fails it's MOT if it's servo isn't working please Geo?
    Yes you are

    I assume the BrakeBuddy works off an intertia switch, am I correct please?
    It has a fully ajustable inertia setting depending on towed mass

    Does reversing cut the BrakeBuddy out of the system please?
    It is claimed you cant revers with an A frame, I can, and have reversed 40 foot in a straight line from between two parked lorries in a service area, the Brake Buddy did not come in (there is a signal given on my dash when it does)
    Has the BrakeBuddy got Eu approval yet please?
    No! its an all American toy
    Watch this space
    Coming up very shortly for there first MoTs are a new breed of electric motor over cable parking brakes on many vehicles, I await any special instructions regarding these,
    We have also been told NOT to fail Import quads with only hydraulic parking brakes
    these clearly fly in the face of Dft requirements but have been EU type aproved:Eek!:
    Geo
     
  15. pappajohn

    pappajohn Funster Life Member

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    and now in english please Geo:Rofl1::Rofl1::Rofl1:

    but why would the buddy kick in when reversing.....there is no inertia unless you dump the clutch:Doh: forgot....you aint got one have you:Wink:

    surely there would be less inertia reversing than than there would be by just taking your foot off the gas going forward under normal driving.
     
    Last edited: Apr 17, 2009
  16. des

    des Read Only Funster

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    the brake buddy instructions say it doesn't operate until about 10mph, but as there is no way it can sense the speed, there must be a threshold of deceleration below which it doesn't work. with regard to the brake pedal force, this is adjustable, and requires the vacuum reservoir to be emptied before setting off. the new vantage model does this automatically by pumping the brake 5 times when first connected. and allows the sensitivity (threshold) to be adjusted from the cab when on the road. great system, no doubt not legal, but in my view the best. sadly, bl@@dy expensive over here.

    des
     
  17. 45eEver

    45eEver Read Only Funster

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    Thank you for your answers to my questions Geo.

    I am very surprised someone doesn't get the TowBuddy approved, Europe's a big market, and tow-frames seem here to stay.
    As you point out, someone got it for hydraulic parking brakes.

    Does your TowBuddy come on when you descend a hill please Geo?

    I gave your brake tester experiment some thought.
    Applying the brake via the A-frame is reasonably simple.

    Assuming the coupling handbrake pulls the same cable as the over-run brake: -
    If you remove the spring assistance to the handbrake, you end up with a simple lever.
    If you pull on that lever with a spring balance, you pull the car's brake on.

    The hitch manufacturer will supply the operational max and min for the relevant hitch.
    It's then a simple calculation to apply the proportional max min via the handbrake lever.

    If the parking brake lever doesn't operate the service brakes, then a more powerful spring balance and a small winch directly pulling directly on the cable would do the job.

    Fag-packet designing an A-frame that steers the towed car/trailer isn't difficult, although the engineering calcs aren't simple, and would vary for different types of cars.

    Reversing a towed car/trailer in a straight line picks you out as the top banana Geo, can you reverse one through an S-bend though?
     
  18. Reallyretired

    Reallyretired Funster

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    Whether or not the brakes are on or off when reversing is a bit academic to me. I have a small unbraked trailer that I take rubbish to the tip in. Because it is proportionately very short, as is my toad smart car, it jackknifes almost immediately on reversing. I have no problem reversing with a caravan, which being much longer is easier to reverse.
    The gist of this rambling post is that if I had an autoreversing brake, I still couldn't actually reverse it.:Sad:
     
  19. 45eEver

    45eEver Read Only Funster

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    Nearly Retired, you can reverse your caravan because you can see the caravan sides long before they get out of line.
    Your caravan, unless was made before April '89, has auto reverse brakes.

    You can't reverse your trailer because you can't see it until it's too far out of line to recover it.
    I suggest you get 4 of those things cyclists have on the back of their bikes so motorists can see them.
    A reflector on a stick.
    If you mount them on the corners of your small trailer body,, stick out sideways, you will be able to see what your trailer is doing.

    The problem with reversing a car on an A-frame is that as soon as you turn slightly with the tow car, the front wheels on the towed car swing over to full lock.
    A bit like the supermarket trolley effect.
     
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