dirty work JOHN ROOTH

4 x 4 Australia - - Contents - JOHN ROOTH

Back in the March is­sue of 4X4 Aus­tralia we had a look at the sort of dam­age copped by the front panel of a 40-Se­ries Land Cruiser that’s used and abused on cor­ru­gated roads. I may have men­tioned we’d be hook­ing in and re­plac­ing all that pretty soon with some new trick en­gi­neer­ing. Yes, and then Chooka showed up look­ing for a counter lunch and the job slowed down.

Life is like that, but with the school hol­i­days on and the lads keen to help (keen to eat more like it!) we got back out to the shed and got stuck in. I’m pretty lucky like that be­cause my sons have reached an age where they’re re­ally use­ful. When they were younger they’d come out and spill paint ev­ery­where and drop my span­ners down the open drain just so they could see the splash!

Metal fa­tigue is what kills many old trucks and sees bits fall­ing off in the dirt seem­ingly for no rea­son at all. Most peo­ple with some bush ex­pe­ri­ence of ma­chin­ery are well aware of it but, if you’re not, well, you prob­a­bly will be soon un­less you live in cot­ton wool.

The best way to ex­plain it is to grab a piece of wire – a pa­per clip is good for this – and bend it up and down. Two things hap­pen: it gets hot at the bend, it gets harder to bend and then even­tu­ally it’ll snap. Hang on, that’s three things. And you thought the only thing I could count was a shout.

Right, what’s hap­pen­ing is that the metal is chang­ing at an in­ter­gran­u­lar level. One sur­face is be­ing com­pressed, the other stretched, and then we bend it back and re­verse the process. En­gi­neers call this fa­tigue load­ing and, like Fat

Kevvy after too many prawns, the re­sult is that even­tu­ally some­thing’s got to take a lit­tle lie down. In the case of metals – and all metals have dif­fer­ent prop­er­ties here, which is why you don’t see too many die-cast alu­minium shock ab­sorber mounts – elas­tic­ity is lost and cracks are the re­sult. Fa­tigue load­ing in­vari­ably means that cracks start on the edge of the metal first – this is what we call a stress frac­ture.

There’s a clas­sic ex­am­ple of that in Milo’s mud­guard in­ner panel. You can see the metal’s copped plenty of dam­age – it’s been flexed so much that it’s cracked in three places all around the mount­ing bolt hole with­out crack­ing the hole it­self. Why’s that? Be­cause there were thick wash­ers on each side of the hole, which held it se­cure. Given time, that bolt, wash­ers, the hole it­self and the nut would have all dropped off to­gether, leav­ing the mud­guard free to beat up the next bolt down the line.

The orig­i­nal Toy­ota 40-Se­ries en­gi­neers re­alised fa­tigue load­ing and that con­se­quent stress frac­tures might be a pos­si­bil­ity in a ve­hi­cle de­signed to be used on rough roads most of its life. So they took sev­eral steps to slow it down. You’ll note I said “slow it down” and not stop it, be­cause noth­ing stops metal fa­tigue apart from leav­ing a ve­hi­cle in an her­met­i­cally sealed bag and never us­ing it.

They used thick, mild steel pan­els for starters. At about one mil­lime­tre in thick­ness, they’re three times as thick as mod­ern pan­els, but strength means weight and that means they had to mount them to al­low for some move­ment. Hence the hinge you’ll see down the front of the front panel on an old Tojo. For the same rea­son, the chas­sis on the old jig­gers were al­ways riv­eted to­gether rather than welded – rivets al­low a lit­tle flex.

In fact, a long-wheel­base 40-Se­ries chas­sis can be jacked up on one cor­ner and you’ll get about 50mm of flex across its whole length.

This flex­i­bil­ity was even more im­por­tant in the days when sus­pen­sion was merely a de­vel­op­ment of the stuff they used un­der horse-drawn wag­ons. Yes folks, the in­tro­duc­tion of coil springs and de­cent shock ab­sorbers was pos­si­bly the largest step for­ward in the bat­tle against metal fa­tigue on off-road ve­hi­cles. Land Rover first in­tro­duced them in the 1970s. But by 1988, when Nis­san re­leased the GQ Pa­trol, met­al­lurgy had caught up – pro­cesses such as coil scrag­ging and shot peen­ing were used to re­duce sur­face ten­sion on the coils that led to re­li­a­bil­ity prob­lems such as break­ages. Man­u­fac­tur­ers ev­ery­where re­alised you could have strength with sup­ple­ness. Real sus­pen­sion was born.

But it was way too late for Milo and, while I have thought of do­ing a coilover con­ver­sion, adding com­plex­ity to some­thing that’s sim­pler than the av­er­age axe has al­ways put me off.

Okay, so now you can ap­pre­ci­ate why good sus­pen­sion is such a crit­i­cal thing for 4x4s that get used se­ri­ously off-road. You see, the more of that con­stant cor­ru­ga­tion pound­ing you can ab­sorb in the sus­pen­sion, the less that gets trans­mit­ted to the chas­sis and then the body of the truck it­self.

So if you want to save money you’ve got to spend on good sus­pen­sion.

Or spend plenty of time in the shed like my lads and I do.

It’s not all beer and skit­tles keep­ing an old truck on the road. Beer is def­i­nitely very en­joy­able when the day is done and you’re some­where very re­mote, though.

1 2 3 1. My son Joe has worked out a way to make brush­ing the rear floor more in­ter­est­ing – he’s lis­ten­ing to pod­casts! Noth­ing knocks a hole in a lot of work quicker than a few help­ing hands.

2. The front panel we talked about a cou­ple of is­sues ago isn’t go­ing to jump out on its own, de­spite be­ing more bent and bat­tered than a ba­nana frit­ter. Lock­ing the mud­guards and in­ners to the chas­sis through a hinge – it’s kind of im­por­tant there’s some struc­tural in­tegrity.

3. With holes cut for the in­ter­cooler and hoses down below, there’s not a lot of the old front panel re­main­ing. It’s been strength­ened with an­gle iron along top and bot­tom sec­tions, but the rest is more bent than a coun­cil full of real es­tate agents.

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