question about drawbars

Submitted: Sunday, Feb 17, 2008 at 10:37
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i'm putting a new chassis under my caravan over easter and i'm trying to work out the drawbar that needs to go on it. does anyone know how you calculate a drawbar lenght, as in how far it needs to go back under the van in relation to how far it sticks out the front of the van. and does where the axel sits under the van relate to what lenght you need to make the drawbar.

any help would be much appreciated, or a good link to working this out.

cheers
RUMPIG
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Reply By: DCTriton - Sunday, Feb 17, 2008 at 10:54

Sunday, Feb 17, 2008 at 10:54
I guess a lot depends on the van itself... I'm no expert but I would be inclined to run the drawbar back to the spring hanger on each side and weld it to the hanger also, reinforcing the hanger itself... If it's a heavy van, perhaps a center bar also running as far back as is practical, it adds stability and is a great place to put the jockey wheel...
AnswerID: 287905

Reply By: Member - Doug T (FNQ) - Sunday, Feb 17, 2008 at 11:00

Sunday, Feb 17, 2008 at 11:00
Why not go ask an engineer/Caravan,Trailer manufacturer.

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AnswerID: 287908

Reply By: Louie the fly - Sunday, Feb 17, 2008 at 11:10

Sunday, Feb 17, 2008 at 11:10
Why wouldn't you duplicate what is already there? That is a generally accepted "engineering best practice". You need to make sure that the drawbar is secured to a few points on each side and the welding is of an acceptable standard. If you are not a competent welder my suggestion would be to employ one.

My experiences have shown that a longer drawbar does generally makes it easier to reverse the trailer, and as your bulk load is further rearward, the ball weight should reduce slightly.
AnswerID: 287914

Follow Up By: rumpig - Sunday, Feb 17, 2008 at 17:20

Sunday, Feb 17, 2008 at 17:20
i'd duplicate what is there, except for the fact it is an old van with a really short drawbar. i'm looking at putting a decent chassis under it which currently it doesn't have, aswell as extending / make a whole new drawbar for the van. problem with making the drawbar as long as possible will be that the axel will be set back a fair way on the van and i'm trying to get the ball weight down. i'm adding a storage box to the front of the van sitting on the new chassis, so due to this the longer the drawbar, the heavier the ball weight will be due to the axel location on the old van. hope that makes sense without seeing what i'm doing.
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Reply By: Derek from Affordable Batteries & Radiators - Sunday, Feb 17, 2008 at 11:13

Sunday, Feb 17, 2008 at 11:13
I would take it back as far as possible and strengthen where you can. A lower tie rail is common for strength too.

I came across this camper a few years ago. The guy obviously needed a better draw-bar. (Amongst other things)



Regards

Derek
AnswerID: 287915

Follow Up By: Crackles - Sunday, Feb 17, 2008 at 14:27

Sunday, Feb 17, 2008 at 14:27
A classic example of too much crap on the drawbar, an all too familiar sight these days on many campers. Also made the mistake of welding the drawbar to the front corners instead of right back to the spring hangers. I wonder what the ball weight was :-))
Cheers Craig............
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FollowupID: 553221

Follow Up By: Member - Hughesy (NSW) - Sunday, Feb 17, 2008 at 15:32

Sunday, Feb 17, 2008 at 15:32
Jeeesh!!! He's got enough gas there to launch a hot air balloon!! The kitchen sink must be inside....next to the dish washer.

Yep, you always have the drawbar extend right back to the spring hangers and never welded to the front corners.

Also need to have the axle positioned such that the ball weight is around 10%.

Good luck.
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FollowupID: 553233

Follow Up By: Skippy In The GU - Sunday, Feb 17, 2008 at 23:43

Sunday, Feb 17, 2008 at 23:43
What do you expect when you use angle line on the drawbar, don't forget this is how the engineers and trailer makers made them for years
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FollowupID: 553326

Follow Up By: Derek from Affordable Batteries & Radiators - Monday, Feb 18, 2008 at 00:28

Monday, Feb 18, 2008 at 00:28
I think it was 75mm sq tube my photo is not all that clear when I zoom and crop.




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FollowupID: 553335

Reply By: Geepeem - Sunday, Feb 17, 2008 at 17:02

Sunday, Feb 17, 2008 at 17:02
HI Rumpig,

I'd also check with your Registration department as they would probably have the specifications. I recently registered an unregistered van in Queensland and as well as obtaining a road worthy and gas certificate I had to physically take van to the Motor Registry inspection depot where they measured all sorts of distances - front of drawbar to first axle, second axle, overhand last axle to rear of van, width etc etc. Presumably there are standards which must be complied with. If you are making it different to original design I would check with them else you may have trouble if it wasn't compliant and had an accident etc. It seems like the simplest way is to just duplicate old drawbar.
Cheers,
Glen
AnswerID: 287968

Reply By: rumpig - Sunday, Feb 17, 2008 at 17:13

Sunday, Feb 17, 2008 at 17:13
thanks for your comments so far,
the drawbar will be connected to the chassis in 3 different places as it goes back under the van (chassis will be a big rectangle, with a few spreaders inbetween), so connection of the 2 won't be a problem at all. as for laws relating to what i can do, i've found a couple of sites that help me out with those. just trying to research more about drawbars themselves. the comment relating to a engineer makes sense, but being a self employed tradie i find it hard to get time away from work during the week, this being the reason i'm after any good website links to help me out.

cheers.
RUMPIG
AnswerID: 287970

Reply By: Dunaruna - Sunday, Feb 17, 2008 at 18:03

Sunday, Feb 17, 2008 at 18:03
We do this kind of job regularly and for the most part we just duplicate although sometimes we add 300 or 600 mm to the overall drawbar length. A stress rail is almost a must these days, we won't do the job if the customer won't pony up for the extra cost.

As for axle positioning, you are governed by the mudguards unless you are going to do major structural and cosmetic modifications.

I suggest you get her weighed so that you can determine the ball weight ratio, don't forget to add luggage/water etc to your final figure. Also, measure from the tip of each axle spindle to the ball coupling, this will tell you if the original chassis/axles are square and true (you would be amazed how many are not). This will give you a reference guide for the new chassis.

Finally, I see cracked and bent chassis all the time. Correct welding/gusseting is a must.
AnswerID: 287984

Follow Up By: Isuzumu - Sunday, Feb 17, 2008 at 18:27

Sunday, Feb 17, 2008 at 18:27
Hi Dunaruna,

I have been thinking of replacing the chassis on my 15 Viscount 1978 model, could you tell me what the cost would be?. It already has a suspension up grade eye to eye leaf springs with shocks solid 2 inch round axlel and 15 inch rims.
Any info be most helpful.
Cheers Bruce
Cheers Bruce
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FollowupID: 553271

Follow Up By: rumpig - Sunday, Feb 17, 2008 at 21:21

Sunday, Feb 17, 2008 at 21:21
sorry if this sounds stupid but that's why i'm asking questions before i tackle the job. what's a stress bar and what's it do? my guess is a bar running lenght ways down the middle like mentioned in an earlier posting, but i've really no idea what it is and what it does.
my plan is to make a complete rectangle shape chassis out of 125mm x 75mm x 3mm RHS (prefer 150mm x 50mm, but it's to high where my step goes), about 700mm back from the front i'll have another "spreader" for the back of the storage box to sit on, aswell as another spreader near the middle of the van somewhere.
so the drawbar will have 3 points at which to attach to the chassis, (1) front cross piece (2) back of box spreader (3) lenghtwise chassis rail back near spring hanger. would i still need a stress bar that you mention?

thanks for all your help
RUMPIG
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FollowupID: 553297

Reply By: Dunaruna - Sunday, Feb 17, 2008 at 20:49

Sunday, Feb 17, 2008 at 20:49
Every job is different, some need a new 'A' bar, some need the whole shooting match, some need raising. Rotted floor ply also throws a spanner in the works. We only quote after a detailed inspection but to give you a very rough ballpark - somewhere between $1000 and $4500.

BTW, I'm one of the grunts in the workshop, the blue-bloods in the office do the quoting.
AnswerID: 288011

Follow Up By: Isuzumu - Monday, Feb 18, 2008 at 07:47

Monday, Feb 18, 2008 at 07:47
Thanks for your answer.
Cheers Bruce.
Cheers Bruce
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Reply By: Dunaruna - Sunday, Feb 17, 2008 at 21:55

Sunday, Feb 17, 2008 at 21:55
The stress bar runs from just behind the coupler to underneath the van, both sides of the 'A' frame underneath. What it does is it turns your drawbar into a stress truss so that it does not bend.

If I get a spare minute tomorrow night I'll post a pic.
AnswerID: 288049

Reply By: Derek from Affordable Batteries & Radiators - Sunday, Feb 17, 2008 at 22:47

Sunday, Feb 17, 2008 at 22:47
Here is a good shot borrowed from another website. Grey-Nomad

Shows the strengthening truss rail and you can also see how far back they have taken the A frame.



Regards

Derek.
AnswerID: 288061

Follow Up By: rumpig - Monday, Feb 18, 2008 at 17:27

Monday, Feb 18, 2008 at 17:27
thanks for posting that pic, explains everything. i'll have to have a look at a few vans on the weekend and get some ideas i think. that A frame goes back alot further than the jayco van i looked at on the weekend, every company seems to do it different.
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FollowupID: 553433

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