Thread: Single axle to tandem?

Just the standard rocker mate. Sounds pretty simple now that you've explained it. Trailer isn't going to be used to carry a lot of weight, primarily just for support so maybe down the track I'll upgrade the axles.

I've bought new hubs and axle and am not too sure how to put it all together. Would you have any links to help me assemble it?

Thanks for all your help so far mate

Here's a pic of where I'm at at the moment. Everything is tacked. The wheels are on as I was just checking the clearance with the side of the trailer. Does everything look okay? The centre hanger is exactly 52" back from the front cross rail. Also, am I able to use the existing drawbar (65x35x2 - showing in Pic 1) or should I opt for something bigger?

With the hub fitment to the axle, is there supposed to be a washer that sits between the small bearing and castle nut? The kit I bought didn't come with one.

The drawbar sounds far too light.

I'd be leaning toward 50x75x3 given the trailer is tandem and you'll load it up.

Remember a tandem trailer will put more sideways load on the drawbar than a single axle trailer.

I've never seen a hub that didn't have a flat washed between the bearing and castellated nut so I'd be onto the supplier..

Originally Posted by zuffen

The drawbar sounds far too light.

I'd be leaning toward 50x75x3 given the trailer is tandem and you'll load it up.

Remember a tandem trailer will put more sideways load on the drawbar than a single axle trailer.

I've never seen a hub that didn't have a flat washed between the bearing and castellated nut so I'd be onto the supplier..

Yeah went with the 75x50x3 drawbar

With the final setting up of the rocker springs, which bolts on the springs should have the 0.5mm clearance in it? The front and rear hangers?

Here's a pic of how it stands atm. Guards haven't been welded on as you can see. One wheel isn't on yet. Is there any way to reduce the gap between the wheels? Or is it fine like that?

Unit,
possibly the tandem rocker set up you have chosen is for 16" wheels, like the 205R16 used as standard wheel sizes on older 4WD utes. If suited for 16", then the what appears to be either falcon or commodore 15" wheels, there is a larger gap between the two.
If you look at the link to Industrial Springs that was provided by Yonnee, on most of the tandem set ups, measurement 'c' is the distance between axle centres (or wheelbase) varies between 778mm to 1065mm, so a variation of 287mm. I'd suggest your axle centres are towards the upper end of that variation.

As it appears your wheels are 15", I've picked the Bridgestone RE92 205/65R15 as an example, it has an operating diameter of 647mm. Therefore the measurement 'c' only need be 647 (2 x radius) plus clearence between the two wheels. The rocker set up with measurement 'c' of 778 would give you a clearence of 131mm (or 5") between the wheels, more than enough.
The closer you can keep the centres together, the easier the trailer will be to turn, plus reduces scrubbing when turning.

As you've allready welded, there is probably not much you can do, although you could artificially disguise the gap by putting 16" wheels on, or find a 15" tyre with a larger diameter.

My 7x4 trailer is tandem, but does not use rocker or load sharing suspension. It was originally shod with 215/R14 tyres. I've replaced the tyres with some LT tyres, have reduced the width, but increased the diameter so now I only have about a 50mm gap between the tyres.

Thanks Yonnee for the Industrial Springs link, it has been very useful.

Unit, I hope I've made sense.

Cheers,
Wahoon.

I'd agree that you may have been given a spring set to suit "Off-Road" (16") wheels, rather than a set to suit "Passenger" (14") wheels. Generally, the springs for 16" wheels have the centre bolt, on centre, whereas the springs for 14" wheels have the centre bolt off centre to bring the wheels closer together. The springs are the same length, so they interchange using the same hangers.

Good decision to up the drawbar size. Give yourself about 5' from the front cross bar out to the point where the two bars meet. Also, tie the outer ends to the front hangers by welding where the drawbar touches the inner vertical front edge of the hanger.

Yes, as Zuffen has stated, there should be a washer between the bearing and the nut.

Originally Posted by Unit_01

...which bolts on the springs should have the 0.5mm clearance in it? The front and rear hangers?

0.5mm?? Not sure what you mean.

Originally Posted by Wahoon

Thanks Yonnee for the Industrial Springs link, it has been very useful.

That's what I'm here for.

Wahoon- The wheels that are on it at the moment are off a VE omega which are 16" (225/55R16). My axle centres are at 970mm.. Everything is still tacked but is there anything I can do to reduce the distance between the wheels without buying a new spring kit?

Thanks for the help guys. Hopefully there is still some way that I can reduce the distance between the tyres

If they've supplied you the wrong springs, then you should be entitled to swap them out for the correct units. The confusing thing now with the trailer industry is that in years gone by, the difference between Passenger car wheels and tyres, and Off-Road wheels and tyres, was simply refered to as 14" and 16". Now, with a number of Passenger cars running 16" rims and bigger, the difference between the spring sets cannot be refered to just by rim size alone. And it's the unsuspecting end user who ends up getting the wrong parts because they're not asked the correct question.

The tray looks twisted in the pic in post #20.

Optical illusion?

Originally Posted by Dan

The tray looks twisted in the pic in post #20.

Optical illusion?

Haha the front left wheel isn't on.

So the tray twists when one wheel is loaded more than the other on an axle?

Hi Unit,
a couple of things you could try;
1. find the dia of your tyres and see if you can find a different profile which increases the diameter.
2. The rocker allready looks to be the short one, you could bring the outer spring hangers in a bit making the shackles at the hanger stand up more vertical than what they are, you'll still get the load sharing articulation.
3. I think Yonnee already suggested this, see if you can get different springs that will bring the centres closer together.
4. Once again, find the dia of your tyres, add 100mm for clearence and see if you can get a better set up than what you currently got.

I have been noticing tandem trailers with load sharing suspension and I think it is just a trait that the axle centres are apart. I've got 4 tandems (including my boat trailer) over my yard, but none of them load sharing, all just basic hanger and slippers so all are reasonably close together.

Most trailers would be flexible enough to twist when crossing kerbs ect.

Most cars have a certain amount of twist in them.

Trucks are designed to twist over obstacles/bumps. If they didn't their chassis would fatigue and crack. This is also why truck trays are bolted on and usaully over timber bearers.

My project car has to got though a test to see what its torsional rigidity is. It's allowed to twist but only at a specified input.

I would think the twist in that photo is quite normal.

Bit of an update on my build. This is how she stands at the moment. Primed and painted. I still have the standard lights but am looking at upgrading them to LEDs in the near future. Anyone got any helpful guides on the installation/wiring of these?