Thread: Help with draw Bar opinions

Hi

great forums!.....ive been reading through all the threads and have formed my own opinion but am keen to hear others

I just bought a car trailer its only 2 yrs old.....the old owner just made a whole new extended drawbar for it only a few months ago

the problem i have is i think the bar could have been made bigger considering its length

from deck to drawbar end it is 2meters....and is made from 75x50x3.5 ....its quite thick but i still think he should have used 100x50

short of cutting it off and building a whole new one (really dont want to do this) i thought the easiest way to put my mind at rest would be to add a third draw bar of the same specs through the middle as per pic below 3rd pic

Install a truss on the underside of both drawbar rails using either 50mm flat or 12mm rod.

I saw this truss idea....one thing i noticed is its only as good as its design.... being it has to be made from decent materials and needs to run the whole length or close to the whole length of the draw bar to be effective.....also no welding across the bars

The implementation shown in that pic looks like the go.

Originally Posted by rod1949

Install a truss on the underside of both drawbar rails using either 50mm flat or 12mm rod.

I would go with this idea as well, it also cuts down on the weight issue. Putting in the centre bar did very little strength wise. If you don't like the idea of a truss underneath stitch weld some 50X50X2.5-3.2 about 3/4 from back of drawbar forward, but be prepared to get the trailer reweighed for rego purposes, as an insurance claim might be awkward.
Kryn

Originally Posted by rod1949

Install a truss on the underside of both drawbar rails using either 50mm flat or 12mm rod.

Now the way I did this was, cut two lenghts of 50mm x 3mm flat near enough the full length (and as you can see running back past and under the front of the trailer), then just lay them flat on the RHS draw bar and weld each end (I did it for about 300mm each end), then lift/pry up the remainder of the flat to measure and fit in a very tight fitting packing block and weld in place.

i like it ^^^ i might use 5mm though

judging by the pics i have seen on the net its extremely important to run them almost the whole length....at least the majority

also to attach then in exactly the same way you have....a good 20cms and stitch along the side

Obviously you can use whatever section you like, but 50x3 should be ample - the steel is in tension and is *tremendously* strong - consider how much force would be required to stretch it. As mentioned, the longer the truss's fixing points, the more effective it is.

I had an axle on an apple bin trailer that was undersized and bowing under full load - a length of 10x2 flat bar with an inch or so high spacer in the middle fixed it, and has held up fine being run daily over rough terrain.

Hey rusty .... Yeh just saw this one (couple of posts down)
Forum | Caravan & Motorhome | RV Tips, Travel, Camping, Swap, Social Chat. - View topic - Check your Caravans A Frame

So no one likes the third draw bar idea? Does anybody think the 75x50x3.5 is good enough as it is ? Some people that have looked at it reckon its fine but when carrying my pride and joy i prefer it to be overkill

Originally Posted by loveit

Hey rusty .... Yeh just saw this one (couple of posts down)
Forum | Caravan & Motorhome | RV Tips, Travel, Camping, Swap, Social Chat. - View topic - Check your Caravans A Frame

Actually, looking at that link, it shows where the truss chord has failed - it's where a spacer has been welded across the chord, and the steel has failed in the heat-affected zone - exactly why we are told to never weld across the drawbar, or the truss chord in this case.

Yet their solution is to replace it with a ridiculously thick section, and then go weld spacers across the chord again. They guy rabbits on about using fancy welding rods 'cause he wants it to be extra strong, but the fact is he's repeated the fundamental mistake that caused the original one to fail.

A third drawbar is a lot of steel for little benefit. A truss is a little amount of steel for a lot of benefit. If you're doubtful about the existing drawbar section, adding a truss is a quick and highly effective solution.

i totally agree.....he says he will repeat the dam thing again and completely missed the fact that it broke because of the support being welded across

its looking like im going to do the third draw bar to mount the spare and add some strength and also do the truss and for supports for truss ill be using 50x25 rhs welded along the drawbar and weld along the 50 (purchased some 40x5mm for truss strap today)

little bit of extra weight but the trailer is allready light and im getting rid of 80kgs of ramps for aluminum planks so not too worried.

I discussed this issue with Yonnee some time back and he suggested that this practice was not recommended as it did not allow the drawbar to flex and so caused fatigue. May pay to check the advisability first.

Dean

Saw a rental trailer tonight had a shorter 100x50 x2mm draw bar very decent bend in the drawbar

Im freaking out now cause my drawbar is so dam long .... Ssooooo much room for bending

The drawbar on a trailer, particularly one that long, needs to flex. If it's not allowed to flex, it will eventually fail. But having a drawbar too light with too much flex will end up just buckling the drawbar. If that drawbar is 3.5mm wall, then it will probably survive quite a bit longer than a similarly sized bar of thinner wall thickness. Adding a truss would certainly stiffen the drawbar, and if the truss was only spaced from the drawbar by only an inch or so, then the truss would possibly have enough flex to make the whole thing work. But the catch22 is that for this to work, the spacers need to flex and therefore need to be flat steel, but you dont want to be attaching them by welding the across the drawbar.
Alternatively, you could go another tack, and 'laminate' the existing drawbar by adding another length of 50 x 50 x 3.0mm underneath, and running 40 - 50mm stitch welds every 2-300mm down the length, effectively giving you a 50 x 125mm drawbar.

I dont mind the idea of the 50x50x3 underneath if you think that will be enough for me to never have to look at the thing again .... I guess thats the whole reason im doing it once its done i want a reliable trailer i dont have to worry about

Will that effectively give me a 125 x50 drawbar ? Or reley too much on the stitch welds