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.
So..............
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.
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.
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.
Jim
-- Edited by JustJim on Sunday 27th of April 2014 02:20:31 PM
Thanks for that Jim, a little info doesn't hurt anyone eh?
This suspension is so simple & if you can't fix it with a welder & a bloody big hammer you're not doing it right.
I notice from your comments re; Jayco that they may be moving to a more complex suspension system.
All Ok I guess until you do break it, as you do.
Then it's a long way to the Jayco dealer as I'll bet the little thingamebob that fits in to the whatsit is exclusive to Jayco only & has to be imported from "that" country that makes everything for the whole world now.
Live axle & leaf springs are so............easy to jerry up &/or replace bits almost anywhere up the track.
Oh well, price of progress I suppose.
regards,
Foz
I've heard your reasoning many times over the years and it's an opinion still held by many. Maybe one day you'll see the benefits of better design and superior performance.
I did suggest using a 'well designed' independent coil spring suspension.. In any market imitators turn up, and there are some poor designs on the market, which give the good ones a bad name.
Keep in mind leaf springs are more likely to break than coil springs, especially with the harsh treatment springs get on rough tracks and corrugations.. If you're in the fortunate position to be able to weld if you're stuck in some remote place, you could probably weld any steel item.
Good design and good engineering should be paramount.Add correct rating, and it means failures are no more likely than the suspension on your vehicle.
Few people would be happy with a sixty year old suspension design on their vehicle, yet they defend an older inferior design on their caravan - mainly with the reasoning that when it breaks (not if it breaks) they can weld it up.
Vehicle manufacturers have been modifying and improving suspensions for over a century now. If they didn't we would still be using full elliptic leaf springs and tiller steering on our vehicles. Imagine that on your new Landcruiser.
Ask yourself why the better built caravans, and the so called 'off road' caravans are all using independent suspensions. It's not to save money - It's to improve performance and safety, to improve the ride quality, and with the right design it improves reliability as well.
Peter..
That gem is fact. When a van with leaf springs on a beam axle sways to one side and compresses one spring, the axle steers the van offline.
If you do some thinking about the function of a leaf spring under compression and rebound you'll understand about axle steer.
Think about what happens to the axle position when you flatten a semi-elliptic leaf spring, with the van swaying to one side.
Had a mate who was a school teacher.
Went to school for 12 yrs, uni for 4 yrs then started in the classroom.
Taught for 30 yrs..........then...................................... given the job as careers advisor as his life experience best qualified him for that role. Hah Hah Hah!
He was of the opinion each & every child should be a teacher, rather a narrow perspective.
There are many "school teachers" out & about eh?
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
