DIY: Easy rider

Find­ing the ideal car­a­van sus­pen­sion and brake setup.

Motorhome & Caravan Trader - - CONTENTS -

Find­ing the ideal car­a­van sus­pen­sion and brake setup

De­spite there be­ing much more ad­vanced sus­pen­sion sys­tems, many car­a­vans are still equipped with beam axles, leaf springs and elec­tric drum brakes. This setup is sim­ple and durable, and is well-suited to heavy-duty ap­pli­ca­tions, but there are other ways of do­ing it.

If you al­ready have the typ­i­cal car­a­van setup and sim­ply want bet­ter body ground clear­ance and ap­proach and de­par­ture an­gle clear­ances, then an axle flip-over con­ver­sion will suf­fice.

The most im­por­tant thing about this mod­i­fi­ca­tion is to not do the work your­self if you are not the tech­ni­cal type. Give it to a qual­i­fied mechanic who is fa­mil­iar with car­a­vans and you will also avoid safety and le­gal con­se­quences down the track.

Most car­a­van beam axles have un­der-slung leaf springs – mean­ing the springs are bolted on with U bolts and at­tach un­der­neath the beam axle.

Some like the idea of tak­ing off the axle and fit­ting it un­der the springs; yes, you’ll in­crease ground clear­ance but this is not rec­om­mended, as you open up the risk of the axle com­ing loose on its U bolts and dis­ap­pear­ing down the road. What’s more, the un­der­body clear­ance won’t change as the beam axle is the same dis­tance from the ground, so you’ll still have clear­ance prob­lems on high-crown dirt tracks.

The only op­tion – with a typ­i­cal car­a­van axle, at least – is to flip the axle over to gain more clear­ance. You’ll still have the safety net of the axle be­ing con­tained within the leaf springs, and you’ll also gain more ground clear­ance than an un­der­spring con­ver­sion, as the wheel stubs will sit below the axle rather than above it.

While the axle flip job adds a rel­a­tively mod­est in­crease in van body height (de­pend­ing on the axle, about 50mm), watch for un­in­tended con­se­quences in­clud­ing hand­brake ca­bles and brake elec­tri­cal

con­nec­tions that are too short (th­ese may re­quire re­place­ment). An an­nexe that no longer reaches the ground and a drop step that leaves too much of a gap to the ground are also po­ten­tial prob­lem ar­eas.

To see if your van will have th­ese prob­lems, it helps to jack it up first to the ex­pected height in­crease and see how it mea­sures up.

There is also the mat­ter of van sta­bil­ity – as you are in­creas­ing the cen­tre of grav­ity you could be mak­ing it less sta­ble than it was.

Another type of beam sus­pen­sion is the tor­sion beam type. While quite sim­ple and com­pact, th­ese are gen­er­ally only seen on some lighter vans as they don’t tend to be as good as leaf springs for heavy haul­ing.

IN­DE­PEN­DENT THOUGHTS

Sim­ple, plain beam axles and leaf springs, when cor­rectly set, do a great job of load shar­ing, ab­sorb­ing road shocks – on smoother roads, at least – and gen­er­ally prove the most cost-ef­fec­tive and durable car­a­van sus­pen­sion setup. If you’re un­lucky enough to break a leaf spring, they can be rel­a­tively eas­ily re­paired to limp home or re­placed with a new one. It’s for th­ese rea­sons that they’ve proven so pop­u­lar.

But if you’ve found your­self tempted to ven­ture down more high-crown dirt roads, or even if you’re just head­ing along paved roads that are rough enough to throw your van and its con­tents around, it might be time to look at in­de­pen­dent sus­pen­sion.

Of course, mod­i­fy­ing your own beam-axle van with in­de­pen­dent sus­pen­sion is ex­pen­sive and would re­quire en­gi­neer­ing cer­ti­fi­ca­tion so, in­stead, it is more a con­sid­er­a­tion for when you are buy­ing your next van.

The in­de­pen­dent sus­pen­sion gen­er­ally car­ries less un­sprung weight than a beam axle, so it ab­sorbs bumps more quickly and smoothly, and it does

not rely on the springs to lo­cate the axle, re­duc­ing the chance of bump steer, that is, trans­fer­ring some of the shock load­ing on the op­po­site wheel caus­ing it to move. Th­ese ad­van­tages all per­mit the in­de­pen­dent sus­pen­sion to pro­vide a bet­ter ride.

There are a cou­ple of in­de­pen­dent sus­pen­sion arm de­signs and four dif­fer­ent types of spring that can be used.

In­de­pen­dent sus­pen­sion has typ­i­cally ei­ther a trail­ing arm de­sign, or an A-arm de­sign. Th­ese sus­pen­sion arms use tor­sion bar springs, coil springs or leaf springs.

If you wanted the sup­plest, money’s-no-ob­ject sus­pen­sion setup for your car­a­van, air springs and A-arms are the way to go. How­ever, load shar­ing of the van’s weight is not as good as a linked in­de­pen­dent (or beam-axle – roller-rocker type leaf spring) setup for tandems.

That’s the the­ory but, like so many of th­ese choices, it comes down to the de­sign in­tegrity of the setup. If it’s poorly de­signed and in­stalled, it’s not go­ing to im­prove on a ba­sic but well-en­gi­neered leaf spring beam axle setup.

BRAKES

Many vans have ba­sic, elec­tri­cally-ac­ti­vated mag­net drum brakes. Th­ese brakes, like the beam axle and leaf springs, are rel­a­tively sim­ple but some peo­ple find they’re not the most ef­fec­tive or sat­is­fy­ing brake sys­tem to use. They’re not al­ways trou­ble-free ei­ther, but that’s most com­monly due to poor main­te­nance or abuse.

Elec­tro-hy­draulic disc brakes give a bet­ter brake ‘feel’, bet­ter re­tar­da­tion and fade-re­sis­tance than drums but, like the in­de­pen­dent

sus­pen­sion, you’re pay­ing a lot more for the priv­i­lege.

The over­ride (in­er­tia) hy­draulic brake sys­tem can be used for trail­ers up to 2000kg, be­yond which the le­gal re­quire­ment for break­away brakes ob­vi­ates the abil­ity to use this de­sign. But it’s not per­fect, as you don’t have any con­trol over the trailer brakes from the driver’s seat (other than slow­ing the tow­ing ve­hi­cle, ob­vi­ously) and the trailer brakes’ ac­ti­va­tion is de­layed by the time re­quired for in­er­tia to act on the hy­draulic ram on the cou­pling. This leads to a rather jerky brak­ing ac­tion.

The law doesn’t stop you us­ing over­ride brakes on a trailer heav­ier than 2000kg Tare, as such, it’s just that it is a le­gal re­quire­ment that the driver has the abil­ity to con­trol the car­a­van brakes in­de­pen­dently from the driver’s seat and also for the car­a­van to have a break­away sys­tem – and there aren’t any means of do­ing th­ese things with the sim­ple over­ride sys­tem.

The next op­tion up the lad­der are elec­tro­hy­draulic brakes, which use elec­tric ac­ti­va­tion of a hy­draulic sys­tem, mean­ing you get the in­stant re­sponse when brak­ing and the stop­ping power of disc brakes. This sys­tem is con­trolled at the ve­hi­cle with an elec­tric brake con­troller, and can have a break­away sys­tem in­stalled just like a van with elec­tric brakes. This sys­tem is not cheap ei­ther, but if you want the best, you have to be pre­pared to pay for it.

Top left: A con­ven­tional leaf spring over- slung beam axle sus­pen­sion setup. Above: flip­ping an axle can be done but it shouldn’t be un­der­slung.

Clock­wise from top left: Tor­sion spring beam axles are quite rare on car­a­vans; in­de­pen­dent trail­ing arm sus­pen­sion with coil springs and dampers is the ul­ti­mate setup; over­ride brakes are the de­fault ba­sic brak­ing sys­tem but are not seen much th­ese days; elec­tric drum brakes are the stan­dard car­a­van brake setup; beam axles with coil springs gives a good ride qual­ity but isn’t com­mon any­more.

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