Thread: Single axle to tandem?

You'll need a new set of spring hangers for the existing axel as it probably won’t be feasible to remove and re-use the existing. You'll also need another axel, springs, hubs, wheels, double length mudguards and re-registration and if you are here in West Australia you'll need brakes on both axels (I'm told that inspectors are enforcing this requirement) along with a new brake assisted coupling. And for all this gear you won't see any change from a $1,000.00.

Here's the link for WA requirements for brakes on both axels http://www.transport.wa.gov.au/media..._VS_IB_129.pdf

Why do you want to convert it?

VSB1 says for between 750kg and 2000kg (GTM), brakes are only required on at least one axle. Invariably for an 8x5 trailer, the axle trammels will be less than 1m, so the axle group rules are the same for a single axle. Only if the trailer GTM is too exceed 2000kg are brakes required on all axles.
Not knowing what your current GTM is, but tipping it is less than 2000kg with a single axle. To increase to 1999kg would require an engineering report. So even with the addition of the second axle, the GTM remains unchanged, even though the trailer may well be physically able to gross 1999kg or more.
Probably close to 20 years ago, I converted Dad's 7x4 single axle to tandem. The driver for doing this was I bent the stub on one side. My purchases were two new axles, one pair of hubs, bearings. 2 pairs of springs and 4 long spring hangers and two slippers and a pair of tandem mudguards. I didn't go the load sharing suspension set up as this means additional maintenence. I did not get the GTM increased, so still technically 749kg, although hauling firewood out of the creek at home, gross mass was probably over 2t, but no bent axle stubs.

So yeah, converting an 8x5 to tandem is worth it, if for nothing more than the added security of sharing the load over the running gear, the ability to limp the trailer somewhere for repairs should a bearing or spring fail. If engineered to increase GTM, then that is a bonus.

Cheers,
Wahoon.

Originally Posted by Dan

Why do you want to convert it?

Mainly for sharing the load as Wahoon stated.

This is the current one that I've got (PBL 13)

PBL Trailers

Thinking of upgrading the draw bars to thicker steel too.

Will keep all posted on my progress.

As Wahoon has touch on, the major hurdle to the conversion is the weight capacity that the trailer is registered to carry. If the trailer has ever been registered, then it will be on record that the VIN for that trailer has a lower capacity than it would have if it were tandem. (You haven't stated whether it currently has brakes or not).
The conversion itself is pretty straight forward, although a little involved. You need minimum an extra axle, additional spring set with long front hanger, and a pair of tandem guards. To get the axle centres right, you'll need to remove the old hangers and re-centre the whole set, so you might be better getting enough hangers to do the tandem set.

Originally Posted by Yonnee

As Wahoon has touch on, the major hurdle to the conversion is the weight capacity that the trailer is registered to carry. If the trailer has ever been registered, then it will be on record that the VIN for that trailer has a lower capacity than it would have if it were tandem. (You haven't stated whether it currently has brakes or not).
The conversion itself is pretty straight forward, although a little involved. You need minimum an extra axle, additional spring set with long front hanger, and a pair of tandem guards. To get the axle centres right, you'll need to remove the old hangers and re-centre the whole set, so you might be better getting enough hangers to do the tandem set.

Thanks for your reply mate. Was reading through your build and it was very helpful. The trailer is currently registered. Sorry, doesn't have its own brakes.

I've got a 6x4 trailer which I'll be getting some parts off to use for the build. By additonal spring set, do you mean the leaf slipper/leaf shackle spring set or the rocker springs set?

You can turn a Single axle slipper into a Tandem spring set by adding a pair of springs, and a set of hangers (short fronts, long centres and rears). To go a Tandem load-sharing set (Rocker, Rocker-Roller) requires a whole new spring set, and more expense.

A 6x4 axle is too short for an 8x5... or are you just using the springs?

Without brakes, the trailer can only still weigh 750Kg fully loaded, no matter how many axles it's got.

Originally Posted by Yonnee

You can turn a Single axle slipper into a Tandem spring set by adding a pair of springs, and a set of hangers (short fronts, long centres and rears). To go a Tandem load-sharing set (Rocker, Rocker-Roller) requires a whole new spring set, and more expense.

A 6x4 axle is too short for an 8x5... or are you just using the springs?

Without brakes, the trailer can only still weigh 750Kg fully loaded, no matter how many axles it's got.

Might just purchase new springs and hangers. Would you be able to link me to the correct type of hangers if it's not too much trouble please? Would rather buy the right thing in the first place. Yeah was just planning on using the springs from it.

Cheers

I'm not sure if you can still get them but I put "flexitors" onto my trailer;
all wheels independant from each other and no springs,
add a hydraulic over-ride brakes & the whole thing stops.

For the benefit of NSW members this swap would require an engineers report on the modification to the trailer.

So getting the capacity up to 1999kg could be a part of the report.

The report would cost you $500.00 plus!

Originally Posted by zuffen

For the benefit of NSW members this swap would require an engineers report on the modification to the trailer.

So getting the capacity up to 1999kg could be a part of the report.

The report would cost you $500.00 plus!

Not just NSW, you'll find that this is the case for most, if not all Australian states.

The stupid part about it is that if you modified the original trailer, converting it from single to tandem and adding brakes, and wanted to increase its registered carrying capacity, you'd require an engineer's report. But if you built exactly the same tandem trailer from scratch, you don't require any sort of certification whatsoever, and can register it to carry 2000Kg.

No one ever said our rules of construction ever made any sense.

Hot Rodding is the same. You can build a replica 1948 vehicle (well it will sorta look like one) and use 1 crossmember from the original vehicle and it's suddenly old enough to not have to pass any ADR tests.

These rules were written by some nong who knew nothing about motor vehicles or engineering.

Originally Posted by Unit_01

Might just purchase new springs and hangers. Would you be able to link me to the correct type of hangers if it's not too much trouble please? Would rather buy the right thing in the first place. Yeah was just planning on using the springs from it.

Cheers

This is the trailer suspension download from Industrial Springs in Adelaide, and Page 22 is the drawing for a Tandem Slipper setup. There's a few places in Brisbane that supply trailer springs, but the setup is the same. Different manufacturers may have slightly different length springs which will change the measurements that are on the pdf, but generally the rule in setting them up is to place the longer centre hanger 100mm rearward of centre (for an 8' trailer), and then set the other hangers up so that the slipper end of the spring sticks out past the hanger by 10mm.

Thanks for that! Any tips on fitting rocker springs? I went with the rocker setup.