Spring over axle conversion.

Submitted: Tuesday, Jan 01, 2008 at 16:25
ThreadID: 53012 Views:16295 Replies:5 FollowUps:4
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I want to do a spring over axle conversion on new trailer but am wondering if I need it to have engineer certificate etc.
Not sure I'll do it if not legal.
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Reply By: blown4by - Tuesday, Jan 01, 2008 at 17:39

Tuesday, Jan 01, 2008 at 17:39
I can't see why it would be illegal if carried out in a professional manner as underslung or overslung are just optional ways of mounting the suspension. You will need to check if the axle is cambered, if not you can just rotate it 180 degrees to get the spring centre bolt locating packer plates on top of the axle. If it is cambered you will need to grind the welds off the packers and mount them on top of the axle and re-tack them in place once the 'U' bolts are tight and you have centralised the axle to the width of the trailer. When you re-tack them you only need about a 6mm tack at the front and rear of the packers. Do not weld them at the sides because this is like welding "across" the axle which is not a good idea. They must be tacked in place because it is they that prevent the axle moving sideways when the spring centre bolt head is located in the hole provided in the packer and the 'U' bolts clamp the whole assembly together. You will be raising the centroid of the trailer slightly by doing this.
AnswerID: 279238

Reply By: Dirty Dan - Tuesday, Jan 01, 2008 at 18:24

Tuesday, Jan 01, 2008 at 18:24
Thanks for all the great info. Have heard of people doing this mod but wasn't sure if it was only legal to hang axle this way because it was manufactured like it from factory etc..... But I think your right, if it can be made hung either way to start with I can't see why It couldn't be changed around with no consequence.
AnswerID: 279246

Follow Up By: Dirty Dan - Tuesday, Jan 01, 2008 at 18:42

Tuesday, Jan 01, 2008 at 18:42
sorry about that pretty new to this just realised the above should have been in one of these
thanks again
FollowupID: 543390

Reply By: 96 GXL 80 series - Tuesday, Jan 01, 2008 at 19:50

Tuesday, Jan 01, 2008 at 19:50
it is better to have it set up that way as it takes the actual carrying weight off the "U" Bolts as the spring is sitting on top of the axel.

Most trailers are made with the under slung spring to cater for the average car or station wagon as a tow vehicle.

Happy New Year
AnswerID: 279260

Follow Up By: Dirty Dan - Tuesday, Jan 01, 2008 at 21:49

Tuesday, Jan 01, 2008 at 21:49
Thanks for the info 96.
I never thought of it like that but it makes a lot of sense.
Takes all the weight of u bolts
It would make the trailer tow more level also.
Thanks again.

FollowupID: 543415

Reply By: rumpig - Tuesday, Jan 01, 2008 at 20:05

Tuesday, Jan 01, 2008 at 20:05
i've done it to my caravan and gained 5" of lift, as far as i know i don't need to get it engineered. just make sure you get new u bolts when you do it, they are cheap as to purchase from a trailer shop and make sure you retighten them after a short drive
AnswerID: 279265

Follow Up By: Dirty Dan - Tuesday, Jan 01, 2008 at 21:56

Tuesday, Jan 01, 2008 at 21:56
Thanks for the reply.
Part of the reason I wanted to do the mod was to raise the height of the top the trailer to suit the height of existing camper tent.
Did a few measurements and hopefully should be able to set up just using outriggers instead of having to raise trailer on blocks under wheels as before.
FollowupID: 543417

Reply By: furph - Wednesday, Jan 02, 2008 at 07:55

Wednesday, Jan 02, 2008 at 07:55
There can be pitfalls in this exersize:
Where the axle is over the spring the clamping plate is pulled up snug to the curvature of the spring by the U bolts.
When the axle is below, the clamping plate is tending to only bear against the top spring leaf at its ends, leaving a gap in the centre of the spring. Flexing of the spring pack as the axle pushes up can cause U bolt loosening and for the spring to break across the centrebolt line.
If you draw a single line sketch of the 2 setups you will see the difference.
The solution (as done on vehicles built with spring over) is to have clamp plates over and under the spring, machined with curves to match the springs.
AnswerID: 279299

Follow Up By: Dirty Dan - Wednesday, Jan 02, 2008 at 19:09

Wednesday, Jan 02, 2008 at 19:09
Thanks for the reply furph.
This is also something to take into consideration.
I'll get started on it this week if I get time and see how it looks.
Understand what u mean but will get a better perspective to see it on the trailer. If the gap is too much I'll have to look into the machining idea.
Thanks again for the info.
FollowupID: 543560

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