Axle underling

mark and kerry · Veteran Member

Axle underling

Possum3 · Guru

Contact Colin Young, Senior Automotive Engineer at www.caravancouncil.com.au/ He would be able to advise with correct information not a guess, or a brother's mate did ??????

CARAVAN COUNCIL OF AUSTRALIA
3 Margaret Street,
Parkdale VIC 3195
T: 0409 865 399
F: 03 9587 1828

caravancouncil@optusnet.com.au

yobarr · Guru

mark and kerry wrote:
Hi does any member know the legalities of under slinging van axles for insurance requirements Ive done mine correctly . I checked with the manufacture who said there was no problem but hesitated to put it in writing referring me to a blue plate man who wouldnt certify it as the Center of gravity is higher,I then rang transport who referred me to the same engineer I asked to certify it so Im going around in circles. Im concerned if I have an accident will the insurance company will knock back the claim Ill have to put it back to standard I guess unless any of you guys have had experience many thanks mark

Presumably you are hoping to put your axle in top of the springs,which is known as "overslung". As Possum has advised,this will raise the centre of gravity,but it also can be a problem if the 'U' bolts break or come loose,as the axle is then free to go walkabout.When the springs are underslung,if the 'U' bolts fail and the axle moves,it still is contained by the spring shackles. Don't know much about the law on this,but seems to me that the physics is all wrong.Will be interesting to see what advice you receive from people who know what they're talking about? Good luck.Cheers.

P.S What part of Australia are you presently in,as I have a couple of contacts who may be able to help.

-- Edited by yobarr on Thursday 12th of August 2021 02:55:56 PM

erad · Guru

There is more to the under or over siting of springs on the axles. There is also a centrebolt which is a bolt designed to locate the spring on the axle and stop it sliding fore and aft along the spring. This bolt goes through the centre of the spring and the head of the bolt locates in a hole in a plate welded to the axle. I was towing a trailer for a friend to Adelaide and I stopped for some lunch in a small town. While eating the snack lunch, I noted that the tyre was rubbing on the front of the mudguard. Luckily, I was in the only town on that stretch of road which had a garage and mechanic, and that guy did a fantastic job in replacing the centrebolts on both sides of the trailer. Not only did he replace the centrebolts he even had some in stock, although I am sure he would have been able to make up some bolts if he had to.

Regarding the under or over, mounting the axle OVER the axle means that the U bolts are under tension all the time. Any impact loads eg caused by hitting a pothole will be absorbed better than if the axle was mounted under the springs. UNDER the springs will slightly increase the twisting loads on the springs, but the U bolts do not take the weight of the trailer load. The trailer I was towing had the axle over the springs, and the U bolts had come loose over time, hence the centrebolt had failed in shear because the axle was able to move relative to the spring. When I got home, I checked the U bolts on my caravan and got a surprising amount of movement. One nut took two full turns to get it tight, the others were not quite as bad. So it is a good move to periodically check the tightness of the U bolts on your trailer springs.

Radar · Guru

Interesting topic.

If the sadles were manufactured and mounted to accept the spring you would think it be ok as my way of thinking heavy semi trailers are mostly and trucks are mounted ontop.

I was only last week talking with a fellow traveler, 4 years on the road and he was saying the only maintance he has done was a coulpe screws here and there but had the caravan transport to a workshop to have the overtop spring modification redone as the orignal caravan place had not done the job professionally now after 80000 ks of towing still going very strong.

Just make sure to have the job done right.

KJB · Guru

Radar wrote:
Interesting topic.
If the sadles were manufactured and mounted to accept the spring you would think it be ok as my way of thinking heavy semi trailers are mostly and trucks are mounted ontop.
I was only last week talking with a fellow traveler, 4 years on the road and he was saying the only maintance he has done was a coulpe screws here and there but had the caravan transport to a workshop to have the overtop spring modification redone as the orignal caravan place had not done the job professionally now after 80000 ks of towing still going very strong.
Just make sure to have the job done right.

If the suspension is assembled correctly it does not matter what position the axle is in - over or under. I prefer axle under the springs as it gives more ground clearance. Either way I always use "antiseize/copper coat" grease on the U bolt threads and cut off excess thread to prevent stone damage - this then makes servicing and or replacing springs or axle in the field , easy . If changing from one style to the other do not turn axle over as sometimes there is in build "toe in" and this will be upset and result in excessive tyre wear. KB