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Knee Independent Suspension


Coromal & Windsor Independent Suspension


A suspension mainly found on Coromal Caravans. It’s a simple independent suspension that needs very little maintenance. It rides on unique leaf springs and these springs only need replacing when they start to sag (anywhere from 60 – 80,000km). It is like the Simplicity system in that it is simple plus seems to virtually never wear the moving components it uses. The swing-arm on this system is different from the other Independent suspensions in that it hinges from the middle of the caravan, so when a spring is starting to flatten out it will let you know by wearing the inner edge of the tyre.



The Knee Suspension you've heard about, used to be called the Symons Suspension, and is a factory fitment to Coromal Caravans. It is manufactured by Melbourne Trailer & Caravan Supplies in Chelsea Heights, Victoria



You may be interested to know - the type of suspension on your Coromal is called a - 'Symons Knee'. (Possibly - 'Symonds')

I believe it was designed by a bloke named Brian Symons, back in the 1960's.
It was fitted on trailers initially and appeared on caravans in the 1970's.

The Symons Knee suspension has the advantage of not suffering from axle steer.

Axle steer is a problem with 'live axle' caravans (beam axle and leaf springs)..

A van is far more likely to roll over with a 'live axle' suspension.
With a live axle van, if the van sways to one side and the spring compresses, the axle shifts position on one side and steers the van offline, which magnifies the sway.

With a Symons Knee suspension, if the spring compresses the wheel doesn't change direction as it does with a beam axle (although the camber changes), so the sway isn't magnified.

The disadvantage of a Symons Knee suspension is the limited wheel travel and the somewhat high wear rate if used on rougher roads.

A well designed coil spring independent suspension overcomes both the wear rate and wheel travel problems and gives the contents of the van a much smoother ride - but at a price.

The only reason all caravans don't have independent suspensions fitted is price.

Beam axles and leaf springs are by far the cheapest - and the most inferior suspension.

It's interesting that Jayco are now very serious about fitting independent coil spring suspension on their vans.
It probably won't be too long before the new suspension is fitted right across the Jayco range.



Hi all,

Just had a win raising my silhouette camper & want to tell the world.

Anyone interested how we did it simply without buggering up the wheel geometry, ask & you shall receive.


As you probably already know the Coromals have a triangular frame pivoting from the van centre to a leaf spring set up at the wheels.

All sorts of suggestions have come up from increasing wheel size to building a separate hanging frame from which the complete suspension system attaches.

Have been pondering how to do it as you can't sling the axle under the leaf pack & there is nothing really substantial on the caravan frame where the pivots sit.


At the wheel end, the stub axle is welded in to the triangular frame.

Cut the old stub off flush with the end of the frame, leaves about 120mm stub, weld brand new stub axles to the bottom of the leftover originals. Weld your new brake backing plate supports to the new stubs. Fit longer U bolts. Dab of paint & she's done.

The amount of solid steel to weld to  (ie: the two stub axles) provides a really strong joint that can't be beat.

Making sure your measurements are written down before you start is helpful, taking some photo's for later reference once you've cut all the good bits off is also a good idea.

Total cost      2X 50mm stubs "B" type Ford      $60

                    2X brake backing plates, pre drilled   $5

                    2X extended U bolts   $9

                    Grinding discs, welding rods etc    approx.   $10                                          Total $84

If you're not confident doing the modification yourself a mate who runs an engineering shop estimates about 4.5 hrs from wheels off to wheels on. This makes the total cost for the mod approx.  $450 - 500 taking in to account you'll be paying a premium for the parts if the shop supplies them for you.

And it road tests beautifully, doesn't whack the driveway on the way in & now I need to buy a step for the door.



You got it. Gets 50mm minimum.

As the engineer said...........you could go up to 100mm by duplicating the set up with a dummy stub/spacer with a gusset to each side of the A frame. Plenty of strength there to absorb the twisting effect.

I'm more than happy with the 50mm plus running high wall L/T tyres gives me an extra 30mm.

 Keeps the camper roof just level with the ute canopy for aerodynamics.

Sorry, no pics.

However...............you can not move the axle below the spring pack. This upsets the wheel geometry.

The old stub axle (cut down) just becomes the 50mm spacer between the beam axle & the new stub axle.

Looking at the axle from front or rear of van you have the beam axle on the top. The cut down stub under it. The new stub axle welded to the bottom of the cut down stub axle so you have 3 layers of 50mm steel top to bottom, beam axle, spacer, new stub.

You achieve a 50mm lift.

Higher profile tyres an extra 30mm, overall lift 80mm

Good luck with it all