How to Make "A" Frames better

[pappajohn]

Very helpful George oh:

hi Brian if the wheels are locked with the steering lock it is then controllable as a 4 wheel trailer, and the braking can be tested on each car to see if it needs any extra help like adding extra cable to the hand brake cable of the car to give more power to the braking, but most will be towing a small car which will have more than enough power from the overrun to be legal without the servo ..

FORDY

hi'
i must point out here that ALL twin axle trailers and caravans have a very short wheelbase in relation to their size so the turning effort is minimal.
two or three blokes can quite easily turn a twin axle caravan on its axis but try it with a car and you got no chance. four wheels in the middle:thumb: or one on each corner

ok, it will reverse in a straight-ish line but reverse or drive forward,with the steering locked, round a t juction and your front tyres will shred in no time as they are being pushed/dragged sideways round the corner but they want to go straight ahead. if ,on the other hand ,you allow the wheels to castor ,at least going forward, the front wheels will follow the correct track but going backwards they will ALWAYS turn to the opposite lock due to the front of the towed car being pushed the wrong way. ie- reverse left, front of car pushed right due to rigid "a" frame, car steering, in effect, thinks its turning right so turns to right.
the rear of the towed car will still turn left as it should but the front will scrub as its in the wrong lock.
over short distances this would be negligable and you should have enough power to overcome the friction but to drive with the steering locked means the tyres will never follow the correct track as they will always try to go straight ahead and will scrub forwards and backwards
it,s impossible to reverse without some tyre damage hence trailers have a very short wheelbase to minimise tyre wear.

as for brakes, i doubt if its possible to get the correct leverage to apply the servo brakes, without vacuum, to full efficiency. try this. find a gentle slope, stop your engine and pump off the vacuum, roll down the slope and see how much effort is required to stop. (make sure your handbrake works)

now for autoreverse brakes. the only way i can see of acheiving this is some type of electric selonoid, perhaps a pin to go through the sliding hitch, to lock the hitch triggered when reverse is selected, just an idea.

im sure someone out there can see my point.

john.

 

[pappajohn]

Hi yes that's the same as I'm talking about. and all good aframes have auto reverse couplers as far as i can see from looking at them and breakaway and hand brake
and overrun. so its just the backing up under control

FORDY

hi fordy,
the autoreverse mechanism is in the brake drums on caravans and trailers and has nothing whatsoever to do with the hitch which only applies the brakes.
when reversing, the brakes are applied as the hitch slide backwards but as the trailer goes backwards one of the brake shoes drops out of place allowing the wheels to turn backwards.
its black magic and i dont understand it but i'v serviced my trailer brakes and thats how it works.:thumb:

john.

 

[GeorgeTelford]

Hi John

Re the pin and soleniod idea ( I think we covered that somewhere, probably here )

anywhoo, it causes several engineering problem's first and major one is that depending one the hitch position you might never achieve the (hitch) positioning to locate pin (for instance) imagine the rig facing downhill pressure will already be pushing hitch into "braking" reversing would only add pressure and you would never get moving.

re the shoe dropping out of place, excelent discription, I did post a picture of the shoe and slider set up, here is a cutaway drawing

Link Removed

you can see how it works here, when the drum is going in reverse it pulls the rear shoe down of the "fish hook cut out" and so no braking, when going forward the drum drags the shoe into locked position henced brakes applied. Like all the greatest idea's its really simple.

 

[fordy]

hi fordy,
the autoreverse mechanism is in the brake drums on caravans and trailers and has nothing whatsoever to do with the hitch which only applies the brakes.
when reversing, the brakes are applied as the hitch slide backwards but as the trailer goes backwards one of the brake shoes drops out of place allowing the wheels to turn backwards.
its black magic and i dont understand it but i'v serviced my trailer brakes and thats how it works.:thumb:

john.

Hi this is exactly why it works on with a car on an A frame it needs the force/momentum of the car to push the hitch in to activate the brakes on the car, but when you revers with an A frame you slowly back up and the hitch will not slide in and set the brakes, but if you were to slam it into reverse and speed backwards then it would put the brakes on. the point is that its not a trailer its an A frame and car,

FORDY

 

[GeorgeTelford]

Hi Fordy


The weight of the Toad and the force of the motorhome reversing will compress the hitch and cause braking, that is why the special shoe set up shown above is required to stop reverse braking, other wise they would just tell you to reverse slowly and not bother fitting autoreverse systems into the hubs.

George

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[fordy]

Hi Fordy


The weight of the Toad and the force of the motorhome reversing will compress the hitch and cause braking, that is why the special shoe set up shown above is required to stop reverse braking, other wise they would just tell you to reverse slowly and not bother fitting autoreverse systems into the hubs.

George

I SEEoh: so how have me and all the other people with aframes been backing up all this time if as you say its not possible i think you should try one first i am saying the brakes on my car do not stop me reversing the toad if you go slow and the toad is not a 2ton van or something although this still may work but i haven't tried it with this size vehicle just my small 800kg atoz i can only say what my setup will do but i know a lot of other a frame users that reverse very well with out the brakes coming on,,i think you will find that the hitch will need a considerable force to set the brakes maybe this is the auto reverse part??


FORDY

 

[GeorgeTelford]

Hi Fordy

If it doesnt brake on reverse then we are back to an ilegal brake set up, ie they have "over hitched" the A Frame which in turn means it will not be legal braking force.

ie if the weight of pushing against the Toad doesnt apply the brakes the Hitch is wrong weighting for the A frame.


How do you back up under control, why doesnt your toad randomly self steer?

George

 

[fordy]

Hi George I'm not saying my one is legal just what i can do with. it i can back up and the brakes don't come on i can stop and the brakes do when going forwards, and if i need to do any major maneuvering then i put the steering lock on with the wheels in line it may scrub the tyres a bit but its not like I'm driving it in reverse all day and tyres for an atoz are less than £20.00 so its not a problem for me, i just cant stand being told that its not possible to do what i am doing when you have not tried it
that's all whether it is legal or not is not a problem until someone gets prosecuted
as its not enforced as yet ,, still i hope you can come up with a way to make them all 100% legal

FORDY

 

[Road Runner]

Hi Fordy


The weight of the Toad and the force of the motorhome reversing will compress the hitch and cause braking, that is why the special shoe set up shown above is required to stop reverse braking, other wise they would just tell you to reverse slowly and not bother fitting autoreverse systems into the hubs.

George

Have you got an A Frame or a motorhome? I have both

Only today I needed to reverse my RV with car on the back about 15 ft and it's not the first time I have reversed with the car on the back of the busjust do it slowly:thumb:

No shoes or hubs (but do remember when old caravans had this system)

Often theory is only theory but in practise

 

[GeorgeTelford]

Hi John

Whethor I have a motorhome or A frame is a pointless aside, I do possess a brain which is more than adequate to think things through logically.

Just as a matter of interest, I tried pushing my car backwards on an apparantly flat surface and it went one way and then the other at random and I can hardly push fast.

But if a motorhome was equiped with a correctly weighted Hitch it wouldnt work and that is the stated point of this thread to Make A frames Better ie legal.

I also remember Dynamo's on cars but dont think its a good idea to go back to using them on new cars

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[Road Runner]

2 RV'er with hands on experience are telling you it's possible.

Only people who have frames and practical experience really know if it's possible.

It may not be legal or right to do it but it's possible

Hearsay and theory is all very well but actual experience is what really happens/matters no matter what your brain is telling you

Pushing by hand is something completely different than by pushing with a 7.5 ton 7500 cc V8 RV oh:

It does help to own something to review it or pass judgement:Sad:

 

[pappajohn]

Hi this is exactly why it works on with a car on an A frame it needs the force/momentum of the car to push the hitch in to activate the brakes on the car, but when you revers with an A frame you slowly back up and the hitch will not slide in and set the brakes, but if you were to slam it into reverse and speed backwards then it would put the brakes on. the point is that its not a trailer its an A frame and car,

FORDY

hi gary,
as i'm sure your'e aware all overrun hitch's work the same way, force applied to hitch, hitch drawtube slides and actuates linkage. brakes applied.
in this instance we can forget autoreverse as were talking about brake activation not a means of stopping the brakes being applied
i just looked in the manual for my IFOR WILLIAMS twin axle 3.5 ton trailer (650kg unlaiden wieght), still an overrun hitch and still the same method of applying the brakes, and it states
- quote" to check drawtube reaction test, push the coupling head as far back into the housing as possible (it will move slowly under steady pressure) on release, the coupling head should slide gradually forward under pressure of the gas filled shock absorber". end quote.
now in my eyes pushing a 800kg car backwards will exert a lot more than steady hand pressure.
i'm not being funny or wanting a slanging match (thats george's dept sorry george)
but i would get the brake linkage checked for correct adjustment.
put a ratchet strap around the a frame and hitch and tighten it up so pulling the hitch in, then try to push the car.

please dont take offence at this post as i'm only putting my point of view across.

john.

 

[pappajohn]

all other arguments aside,
apart from tyre wear, does it really matter which direction the front wheels point while reversing. the front of the car can only go where the "A" frame points it... if my old landy disco could push my 1ton suzuki jeep(on a homemade, unbraked "A" frame. ILLEGAL, who gives a stuff) backwards with the wheels in full lock i'm sure a 7 / 8ltr RV wouldn't even notice it was there.

john.

 

[justme AKA Grath]

all other arguments aside,
apart from tyre wear, does it really matter which direction the front wheels point while reversing. the front of the car can only go where the "A" frame points it... if my old landy disco could push my 1ton suzuki jeep(on a homemade, unbraked "A" frame. ILLEGAL, who gives a stuff) backwards with the wheels in full lock i'm sure a 7 / 8ltr RV wouldn't even notice it was there.

john.

Hi John.
Dont want to start any agro, but I wouldn't want to drive the car afterwards

 

[Suzy]

Neither do I

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[GeorgeTelford]

There are going to be no argumentative posts from me, Papajohn as already re affirnmed the same thing I did, so if you can reverse and its not braking then the hitch is not working properly......

Keep it lighthearted fun and informative

No need for personal comments at all.

 

[justme AKA Grath]

Why?

I am sure that you do not need to ask that question

 

[Road Runner]

I am sure that you do not need to ask that question

Why?

3 to 15 ft with the steering lock free and if any resistance stop immediately.

we all get into tight spots

 

[pappajohn]

Hi John.
Dont want to start any agro, but I wouldn't want to drive the car afterwards

SUZUKI SJ410's are never a problem, graham.
they're made of recycled girders and blacksmiths anvils and they run on iron brew. :thumb:

 

[justme AKA Grath]

Why?

3 to 15 ft with the steering lock free and if any resistance stop immediately.

we all get into tight spots

The post implied that the car would be reversed with the wheels on full lock so just immagine the damage to tyres and ????
Oh, I do sometimes drive the big a frames HGV so I do know what I am saying although I do not tow with my mh

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[Road Runner]

all other arguments aside,
apart from tyre wear, does it really matter which direction the front wheels point while reversing. the front of the car can only go where the "A" frame points it... if my old landy disco could push my 1ton suzuki jeep(on a homemade, unbraked "A" frame. ILLEGAL, who gives a stuff) backwards with the wheels in full lock i'm sure a 7 / 8ltr RV wouldn't even notice it was there.

john.

Does the braking system not operate in the same manner as the four wheeled trailer.?

When I reversed my twin axle caravan could almost rip the tyre off if going overboard.

You need to use a bit of common sense surely?

 

[justme AKA Grath]

:thumb:

SUZUKI SJ410's are never a problem, graham.
they're made of recycled girders and blacksmiths anvils and they run on iron brew. :thumb:

You could send me a bit of that Iron Brew

 

[Road Runner]

The post implied that the car would be reversed with the wheels on full lock so just immagine the damage to tyres and ????
Oh, I do sometimes drive the big a frames HGV so I do know what I am saying although I do not tow with my mh

But then you use common sense you can feel the car moving freely (i'e no resistance) cant do it everytime.

If MY post implies anything different I am sorry.

Best look at the next meet rather than argue eh?

 

[justme AKA Grath]

But then you use common sense you can feel the car moving freely (i'e no resistance) cant do it everytime.

If MY post implies anything different I am sorry.

Best look at the next meet rather than argue eh?

No need to be sorry, but there is a difference between a person that has a feel for things and a person that would just use the brut force

 

[Road Runner]

No need to be sorry, but there is a difference between a person that has a feel for things and a person that would just use the brut force

OK you win

Mind you brut force and HGVs

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[Tony Hunt]

The number of motorhomers now towing small cars on A frames must run into thousands now judging by how busy the installers always are. I went the trailer route to start with and dismissed it as a totally unenjoyable experience much akin to towing a caravan. I sold my trailer after a year and went the A frame route with all the benefits it brings. During the several years Ive used it I have only had to reverse out of a tight spot twice, once when tom tom took us up a lane that ended up at a disused and locked level crossing and the other time when we entered a garage in switzerland and were confronted with a height barrier to get out which I didnt spot soon enough. On both occasions a quick uncoupling and a turn around solved the problem. Two or three times I have overshot fuel pumps and have reversed several yards with no problems.
Somebody mentioned earlier about the fact that the majority of caravanners cant and wont reverse their vans, god knows what they do in an emergency situation. I'm quite confidant that I could get my rig reversed and out of trouble If I had to in a similar situation.
This may all be a grey area as far as being legal, I will continue as will I'm sure every other owner who owns an A frame until a court of law decides officialy that it is illegal.
A similar grey area revolves around driving a large RV over 7.5 tonnes on a car licence legally. I have such a van at home that we live in on our nursery as a static because I only have a car licence and am not as confident on this issue and its legality as I am with the A frame.
I know on other forums over the years that George argued blue was black on this issue and was adament that there was no question of it being illegal to drive a large RV on a car licence and that nobody had ever been challenged on this one either in a court of law. We will all have to stay innocent until somebody is proved guilty at some time in the future.

 

[Road Runner]

Good point Tony and those at the rally will see I use a jockey wheel with my A frame and manoeuvre the car around with it on detached from the RV and in fact had to do this at Eurotunnel on the way home from France when they expected me to do a U turn onto the trainoh:

 

[pappajohn]

The post implied that the car would be reversed with the wheels on full lock so just immagine the damage to tyres and ????
Oh, I do sometimes drive the big a frames HGV so I do know what I am saying although I do not tow with my mh

my point is, how many times do you have to reverse and for how far?????
10ft........15ft.......and how many times.....once/twice a trip......once /twice a year..

dont forget the wheels will also rotate slightly due to castor/camber geometry as they are scrubed in full lock so you wont get flat spots.
if you have to do a screwturn in your artic do you need new trailer tyres after a couple of screwturns. no......how many times have you seen an HGV with a failed brake actuator or over adjusted brake leave 100ft of rubber on the road, do they fit a new tyre.....no...so a few feet backwards in full lock will be minimal tyre wear..
if you reverse in a dead straight line then fine, the wheels may stay straight.....but reverse round a corner and you get full opposite lock. period.

john.

 

[Road Runner]

I have only ever attempted to reverse straight backyards and only in an tight spot where it would be the easiest and quickest option.

By no means an everyday option (detaching is the best way)

I have only tried to say you can in certain circumstances.

 

[GeorgeTelford]

This may all be a grey area as far as being legal, I will continue as will I'm sure every other owner who owns an A frame until a court of law decides officialy that it is illegal.

I know on other forums over the years that George argued blue was black on this issue and was adament that there was no question of it being illegal to drive a large RV on a car licence and that nobody had ever been challenged on this one either in a court of law. We will all have to stay innocent until somebody is proved guilty at some time in the future.

Hi Tony

there is a major difference though, with the licence it is because it is not against the law, the AFrame is clearly contrary to the express regulations regarding braking etc.

So with the A frame I can clearly show the regulations proving its ilegal (does not need to be proved in court) and with the licence issue the other thread shows just as clearly why it is legal (tho not advisable) to drive a huge motorhome on a car licence)

Hope that clarifies the issues :thumb:

George

PS I have never argued black was blue, only that the regulations are clear

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