How to raise a trailer suspension
It is not unusual for caravan owners to increase the load in their rigs over the years with new appliances and whiz-bang new parts.
Low mudguards touching tyres are a major problem for the boat trailer and box trailer owners.
Increasing caravan load will increase leaf spring compression further lowering your caravan.
The question many owners face is ‘how can I lift the trailer suspension and return it to normal?’
What are the things that can go wrong?
A strange, occasional noise was a tyre hitting the top of the wheel arch when a pothole jumped up and smacked it!
Cause: An increase in tyre size reduces the gap between tyre and mudguard. Shock loading from a pothole causes the tyre to impact the mudguard upon spring rebound.
Video
A good video on what to expect from a caravan expert when flipping the axle to raise the suspension height.
Lift the Van
The solution to the tyre hitting the mudguard problem is to remove the axle from on top of the leaf springs to a new position, under the leaf springs. Commonly called an underslung axle or axle flip.
When flipping an axle, all of the braking equipment needs to be de-installed then re-installed. Axle spaces welded onto your axle will auto-locate it under the spring centre bolt.
As a precaution, we recommend replacing the standard set of U-bolts with a heavy-duty set of U-bolts.
Purchase a set of replacement U-Bolts here.
Creating more ground clearance works a treat, or did I open up a can of worms instead of fixing the problem?
Finally, when lifting the caravan, you will also need to review the tow ball position in relation to the towing coupling. The receiver bar may need to raise.
Annexe
Raising the height of your caravan could prevent your annexe from reaching the ground.
Inverting the caravan axle will lift your annex and perhaps prevent you from pegging the sides into the ground.
Measure your annex before inverting the axle to avoid surprises.
Warranty
Caravan manufacturers install axles on top of the leaf springs for safety reasons. The U-bolt clamps correctly installed and re-tightening, after the settling period, should last forever.
When u-bolts are manufactured incorrectly, u-bolt breakage can make everything go wrong; u-bolts may suffer from hydrogen embrittlement. It occurs when steel is bent and not de-stressed.
Hydrogen embrittlement and retightening of u-bolts is another issue we talk about in this article.
Axles installed on top of the spring are secured within the boundaries of the springs, should u-bolts break.
Should an under-slung axle detach from the caravan upon u-bolt breakage, disastrous consequences occur.
One way to ensure against the unforeseen is to install a set of heavy-duty u-bolts. Purchase here.
Flipping the axle has been a hot topic for decades, but now you have industry opinion.
There are other alternatives you may want to learn about your caravan height, read on.
Shock Absorbers
Caravan Shock Absorbers – Click the image to purchase.
Axle inversion will lengthen the shock absorber stroke lengthened.
Therefore it is likely a new set of shock absorber will be purchased and installed by your service mechanic.
The top hanger may need to be moved to achieve the correct stoke or a longer shock absorber will be required.
Please watch the video for further identification of the issues here.
Springs
Check your spring height, the spring pack and the thickness of each leaf spring. Ring your manufacturer and ask him about your spring camber height.
Then, draw a line across the top of your spring eyelets and drop a perpendicular from the centre, this measurement is your camber.
Camber can be as much as 120mm. If your springs are flat, then your answer may lie in spring replacement because you have little or zero camber.
Check with your engineer about lifting heavier caravans you may need engineering certification when upgrading.
Learn more about springs here.
Longer shackle plates
Another myth is longer shackle plates will lift your caravan height.
No, that does not work either. Hangers are welded into position according to your spring length, rocker centres, and shackle length. As a result, any change alters your spring dynamics and performance characteristics.
Check this article to address spring hanger locations and how to position hangers correctly. Incorrectly located spring hangers are not uncommon. This information will help you better understand your suspension.
Is there a Safety Standard for U-bolts in Australia?
No, there is NO Safety Standard for U-bolts. However, Couplemate decided to make a testing standard due to stress fractures caused by hydrogen embrittlement.
How does Couplemate test U-Bolts?
Yes. U-bolts are batch tested after galvanising and then de-stressed in an oven. This process removes the stress fractures that develop during galvanising and heating process.
Consider an upgrade from 1/2″ u bolts to 5/8″ u bolts. (CM600-CM604)
The rating for 5/8″ u bolts kits is 2.25t.
The Ultimate Solution
Finally, purchase a pair of small safety chains, if you do decide to under-sling your axle. Weld the chain between the axle and the front spring holder, behind the backing plates.
The safety chain will prevent the axle from causing a create deal of damage and even death as a result of the caravan becoming detached from the tow vehicle through u-bolt breakage.
Hello Bill,
Overlay axles can be inverted on Caravans and Trailers provided they are not used in an offroad situation. Normal highway use does not apply unforeseen forces on stub axle welds, however, additional shock loading forces can occur offroad. We do not recommend inverting overlays in this situation.
after 40000k i find that front right tyre only a little worn , has been scuffed to about a 1/3 of the tread , now useless , is this a instead of on top problem that occurs with the springs being under the axle
Hello Denis, You are quite right, if your axle has a camber then scrubbing of tyres occurs. Couplemate does not build overlay to drop axles with cambers.
Hello Denis, Thank you for your question. Scuffed tyres can be caused by many issues including overloading, alignment, camber and faulty manufacturing of an overlay axle. Call your local caravan repairer and ask if he can perform a chassis triangulation. This will exactly identify the problem.
can your layered axles axles be used to raise a caravan ? ie on top of the springs with short stubs down.
Hello Bill,
Overlay axles can be inverted on Caravans and Trailers provided they are not used in an offroad situation. Normal highway use does not apply unforeseen forces on stub axle welds, however, additional shock loading forces can occur offroad. We do not recommend inverting overlays in this situation.
Hello Bill, The short answer to your question is no. Some manufacturers install camber into their overlay axles. This procedure was popular many years ago. Couplemate does not build in camber as we prefer to match the axle setup to the customers desired load. We suggest customers build their setups to 15% under their ATM. But back to your question, if you invert your existing axle, it is likely you will increase tyre wear.