The building of the Tri-axle Trailer for Piglet

The building of the Tri-axle Trailer for Piglet

Well after much deliberation we are going to build a new trailer, the reasons are many but principally to reduce the risk in carrying the 4x. With the design rules prohibiting moving the axle group far enough forward to reduce the draw bar weight and getting close to the maximum design weight it really should have been a simple decision. That said the logistics of building a new trailer are enormous.

The old trailer

– Tandem axle 3500Kg GTM with 14′ wheels and electric brakes, open deck.

– Low loading height, long ramps and easy of access to tie down the 4x


– Over loaded, over-length, and narrow due to the supporting rails inside the wheels (due to the wide side steps on the 4x)

– The tyres although have not failed, have become hot during use on long highway runs and  the fear is that with extended trips in central Australia that this will only get worse, their small diametre only compounds the problems as there is just not enough tyre to dissipate the heat.

– No dedicated storage places for tyres, tools, push bikes, Kayaks, Tinny, tinny trailer etc.

– No provision for reverse cameras, or reverse lights.

The new trailer – Tri-axle 4500 Kg GTM with protection at the front (critical as the 4x will now have to be reversed on to distribute the weight legally.)  the extra 1000Kg will be partly taken up by the weight of the extra axle, bigger wheels and support frame, but will add a little extra carrying capacity (approximately 600Kg I am hoping so the new carrying capacity will be about 3600 Kg )

Steel and axles ordered today

All nicely primed ready to cut into the required lengths, This Australian made steel was supplied from Orrcon Steel at Banyo and not only were they price competitive against the imports but when there was a issue with the lengths and taking them home on the trailer, they delivered it all for free.

WOW a lot of difference between the 14" and the 16" wheels

One of the main reasons for the new build was to move to a larger wheel, with the concept of a larger rolling circumference allowing better heat dissipation. The new 16″ wheel tyre combination have a load rating of 1400Kg each and in conjunction with the parallel Jap bearings will have a significantly higher service life. This is critical as the three axles will scrub heavily on tight turns and the integrity of these bearings is paramount to the security of the build.

Lining up the suspension

Normally the chassis would have been completed been built prior to putting the suspension together, however as it was important to get the widest possible chassis (to allow for the side steps on the 4x) I assembled the axles and suspension and measured the clearances prior to tacking and squaring up the chassis.

Detailed drawings are critical to the plan

The plans were a little more detailed than the mud map would suggest but it is handy to have some of the critical dimensions at hand to confirm during the build process.

The first tack

After a full day of measuring, assembling, adjusting and reassembling the first tack was used to ensure the outside rails remained parallel and in line with the axles, from there the chassis can be squared off and tacked to hold it all in position to reduce the distortion from the welding.

Welding the underside

Welding the Underside

All going great guns until a minor issue with the welding torch brought it all to a crashing stop, unfortunately cannot roll it over until the braces are completed and the last spring hanger is fully seal welded.

The draw bar is cut to length and will be positioned after some deliberation on what the exact length of the trailer will be. The pinch point of the corners of the front of the trailer and the rear of the motor-home has been moved considerably closer by virtue of the trailer now being wider (boxed section) than the original open design where it was the width of the bull bar that became the closest wide point to the rear of the Motor-home

Just a little more then ready to roll out

All will be ready to roll out upside down, then turn it up the right way, roll it back in and work on the top surface and structure that will hold the tinny and the protection screen at the front of the trailer.

After welding the underside it was time to roll it over, well that wass certainly easier said than done, previously I had only built tandem trailers and had just tied a rope to one side put up a post to act as a pivit point tied the other end to a car reversed and brought it right side up.

This however was a little more challenging, with three wheels on the one side it just wanted to slide across the grass and not dig in enough to let the other side rise.  Desperation is the mother of invention, and by pegging down the side closest to the 4x was able to get it to stop and slowly roll over.

Managed to get it vertical but it was too stable to bring over gently by hand sitting on the wheels. then by a little more from the winch was able to get it to the balance point, holding it long enough to then move in to slow the fall from that point. It bounced a little and was ready to push back into the shed.

Again easier said than done, even without any weight on it, turning it around without a car attached due to the three axles was near impossible.

Now to work on the guards; unless I was to have some guards custom made at horrendous prices I was limited to buying guards for a tandem and modifying them, as the top is to be used as a walk area they would have needed reinforcing so to cut them in half and put some floor plate as the top surface was the plan.  It was at this stage that the guards were measured. the original allowance for 250mm wide was fine and the guards were 300mm wide, this would have resulted in them being over width (Whole trailer is limited by law to being 2500mm wide maximum)  This gave the opportunity (though much more work) to strip one side of the guard off that could then be used on the outside in the gap between the two halves of the original guard.  Now the guard would be sung against the chassis enabling an easier fill section later.

Guards in pieces

Guards cut up and tacked with centre piece

With the width now correct the guards tacked in place and ready for the top section and infill.

Guards tacked in position

To enable the chassis to be as straight as possible when loaded it is intended to create a camber in the section so that the chassis is dipped in the middle looking length ways. to assist the weldment contraction complete this the chassis was put on stands (each end) and will have the top section fully welded thus pulling the ends upwards.

The height of the pintle has been a source of contention throughout the build, without knowing how much the height of the trailer will decrease when fully loaded it is a bit of guess work (Spring compression and tyre bulge) so with this estimate made the height of the tow attachment checked against the motorhome the pintle could be finally tacked into the plate.  This necessitated in preparing it so it was flush with the top surface. As this required a full penetration joint for the connection it resulted in very large double bevel preparation, this in conjunction with the rounded nature of the cast steel pintle is going to require a substantial amount of weld metal. as this has to take longitudinal loads of up to 4500Kg and lateral loads of similar amounts there was no opportunities for compromise.

Pintle and attachment plate

The full penetration joint with limited gap was welded in the vertical position to maximize the penetration of the root run

As the drawbar has not been attached it was easy to turn it over and weld the attachment plate in position.

With the drawbar now tacked in position it is time to weld up as much of the joints as possible and start on the outer frame.

With the frame now secure the storage boxes can be positioned and the brackets for the wheels placed.

Cutting the floor plate to suit

Chequerplate for floor

With e floor plate cut and cleaned up the top surface of the chassis is ground flush and the joints that will be inaccessable later coated with a zinc rich primer.

Chassis primed ready for floor plate

The floor plate is then welded into the chassis and the guards have their top welded on and supports provided on the underside.

Mug shot -

Mug shot of a Mug

infill sections for wheel guards

The sections not only provide a barrier from the dirt and mud thrown up from the wheels but provide a substantial support for the guards, that will be the main walkway when the trailer is loaded.

Pintel connection and hand brake assy finished

By cutting into the attachment plate the handbrake can be mounted further to the front allowing more room for the mounting of the boat motor support that is to follow.  The jockey wheel is now welded in position again as far forward as possible.

The two main tie downs (front of trailer rear wheels 4x) will be taken from the old trailer, these are a sturdy easy to use system and by replacing the webbing they will be as good as new.

The other tie down (rear of trailer) will be a standard ratchet arrangement built into the floor so they are positively located and angled so they will not fray or rub.

As the vehicle has to be reversed on, and that makes it just that little harder to line up guiding rails are positioned so the vehicle will self align as it is reversed in the trailer into the tie down points.

Side showing tyre rails

Welding in the frame supports, as the top frame will have to be welded at a later stage (too tall to get out of yard fully assembled, As the access to the workshop is beside the house where there is a pergola the issue of height meant the top had to be created in two parts, to be welded together after passing through the pergola.

Designing the top framework so that the tinny can be taken on and off with ease was based on the tinny tosser on the 4WD system. by creating similar attachment points i was able to use the same ramps and make an extension piece.

top of trailer

Then the clearance lights and reflectors were placed.

Wiring and fixing the safety signage

Signs on back

then came the time to put the sheet metal around the front of the trailer. although this is just a stone guard it is important to keep it looking nice and a fair effort was made to bend the material (by hand) with the greatest accuracy possible.  Although there was a bit of compromise by not getting this formed by machine it enabled it to be built to a cost.

Unfortunately the Teflon runners were forgotten when the top was at ground level, so they had to be fitted . the rope run through the guides and ready to go.

Front of trailer showing panels

Now that it is basically completed just a couple of extra reinforcing pieces were added, the electric brakes wired and all tested, ready to take to the inspection house for the RWC and then Registration.



Taken leave of our senses, please leave a note for when we return
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