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Getting more flex from the front?


Chicken Drumstick

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Mountain goat vs multi purpose utility vehicle?

Anyway - for my purposes the suspension is fine. What I'd prefer they'd worked on, is the ability to tow a trailer through a muddy field. Differential locking or limited slip as standard, or traction control etc.

G.

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I don't want to question Bill as he's undoubtedly got the knowledge and experience (and is something of an engineering hero of mine), however I do feel it's something of a pet peeve of Bill's that's not as big an issue (for most people) as perhaps it is to Bill (...)

I don't think that makes anyone "right" or "wrong" on the subject, everything is a collection of compromises and

(...)

I've posted before on this subject an article from a US mag where they showed people how to convert their front-shackled vehicles to rear-shackles for various reasons, real or imaginary, so it cuts both ways.

^^ what FF said ^^

Now, these front vs. rear shackles theories really got me curious, I've chatted with Timm C for a while and he never suggested me to fit shackles up front on my 109",

given his experience and skills there has to be be a valid reason...however Bill says the contrary, for the reasons he explained already.

I'll have some more reading about the subject as I'm still new to leafsprings, hopefully I'll get a clue and make my own opinion...

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I relatively recently read an argument put forth by an American offroad identity, Bob Chenowith in favour of front shackles, which aside from some of the stuff I have already mentioned, also goes into the 'Leading'/'trailing' arm effect of the 2 shackle placements. I searched Pirate last night but can't find the article now. Anyway, he likened the 'front' shackle arrangement to that of a radius arm (rangeRover/defender) suspension, where torque produced at the front axle housing, via the radius arms produce a squatting effect at the front of the vehicle to counter the natural tendency of the front to unload on climbs. 'Rear' shackles were compared to a system where the radius arms were fitted the opposite way around and ran forward from the front axle to the chassis, and in this case,axle torque produces a lifting effect on climbs. One could argue as Jamie does that on steepish gradients, the front axle wouldn't have sufficient traction to produce the squatting/jacking effect, but I disagree. An unlocked leaf sprung Landy would struggle to climb even a 15 degree loose gravel slope in only rear wheel drive, but in 4WD would make a fair fist of climbing a 30 degree slope, so the front end is contributing a significant amount of torque to propelling the vehicle forward. Whether or not either system produces the effects mentioned may be debateable, but 2 things are reasonably clear, The trailing arm effect of 'rear' shackles doesn't produce front end 'squat', to counter the natural tendency for the front to unload on climbs. And the leading arm effect of 'front' shackles doesn't produce front end 'lift', to worsen the tendency of the front end unloading!

I also disagree that Landrover's traction and climbing ability in reverse gear is inferior to when driving forward. In my experience it is the opposite and much more easily demonstrated with short wheelbase versions, the main limitation to thorough testing between forward and reverse being the weak front halfshaft universal joints.

Whilst I have seen the occasional Toyota kink/break its front springs or shear off its transfercase in similar scenarios of hitting a railway sleeper at speed as Jamie described, it isn't that common when one considers the many thousands that thunder along our outback roads at 70+ MPH, and I put some of the blame for those failures down to the sliding joint on Toyota's propshafts being too precisely made, causing them to hydraulically lock when plunging as they need to do when impact forces move the front axle rearwards.

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Sounds very logical to me. The comparison to radius arms would mean that one would best be of trying to keep the part of the spring that fixes to the chassis as flat as possible. This would keep the roll axis as flat as possible and should help with climbing boulders and such, and good for onroad handling. So you almost have to go spring over to be able to run relatively flat springs.

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Sounds very logical to me. The comparison to radius arms would mean that one would best be of trying to keep the part of the spring that fixes to the chassis as flat as possible. This would keep the roll axis as flat as possible and should help with climbing boulders and such, and good for onroad handling. So you almost have to go spring over to be able to run relatively flat springs.

Yes, I agree that flatter springs and SOA work better not withstanding the 101 experience mentioned earlier. Due to plenty of clearance between front axle and engine, the issue with 101's can be addressed by fitting a RR/Defender radius arm to the centre of the axle, running back to a suitable mounting on the chassis.The radius arm chassis bushings have sufficient compliance so as not to conflict with for/aft axle movement with spring flex, and the 'leading arm' effect would counter the jacking effect of having the shackles at the rear.

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I also disagree that Landrover's traction and climbing ability in reverse gear is inferior to when driving forward. In my experience it is the opposite and much more easily demonstrated with short wheelbase versions, the main limitation to thorough testing between forward and reverse being the weak front halfshaft universal joints.

I don't mean climbing a hill where the heavier front and different weight distribution come into play where, yes they do climb well backwards, I'd agree, probably better even but I mean in a flat field with the vehicle completely level try and drive up an 18" step with both wheels touching it. The only difference being the position of the shackles.

I'll go with the jacking / squatting effect described too, a resolution of the moments (torques) present would confirm this.

Say we want to look at typical forces of a two ton 4x4 driving up a steep hill.

Lets take a half ton or thereabouts force required to drive our two ton vehicle up a slope. You'd need to be in low range to develop half a ton of pull in a series, probably low second which if I'm aiming for optimum hop would be about right. Too steep and not enough weight, to flat and no hop.

Lets also go with Bill just now and say the torque on both axles is even, the front with the engine, winch, bullbar and lets throw on a high lift is heavier than the rear so we don't need to work out the exact slope and the relative weights of each axle.

Then each axle, both front and back is contributing a force of 250Kg at the tyre including any slippage.

Lets also say the effective radius of our tyres is 15" since we let some air out our 33" tall tyres as the series UJ's don't want anything bigger.

The torque the axle is applying to the leaf spring / radius arm is the tractive effort or rim pull x the effective radius of the wheel.

T= (250Kg x 9.81 (Force is in Newtons not Kg, 9.81 is gravitational constant)) x (15 x 0.0254 to make it metric like the force)

T= 2452.5N x 0.381m

T=934 Nm or 689 Lb ft of reaction torque on each axle housing

The front spring eyes on the chassis to the centre line of the front axle on a series is 0.88m if we say the front springs are symmetrical and under optimum hop conditions the front axle is in the middle of it's travel so the spring is nice and bent and lines up with the middle of the bumpstop.

Using our torque relation above we can say that if torque is force times distance (8Lbs ft =2lbs x 4ft) then we can also say that the force is the same as torque divided by distance (2lbs=8lbs ft / 4ft)

Our Landy climbing the hill of a steepness that requires 934Nm on the front axle then the reaction of the spring on the chassis is 934Nm / 0.44m = 216Kg

So 216Kg is trying to lift either the front bumper and / or 'pull down' the bulkhead outriggers depending on the suspension design.

If you're with me so far then you'll realise the significance of the above statement. It's essentially put numbers to what people call anti dive or ant squat depending on whether drive or brakes is involved. Instead of climbing a hill, exactly the same process is involved in calculating the numbers from braking force as well.

If we were discussing radius arms or link suspension you wouldn't be hearing any arguments from me about all this.

A solid bar like a radius arm on a coiler can indeed 'suck down' the front with a force in this case of 108Kg on each bulkhead outrigger (ignoring different lengths of arms and springs for the moment).

With a solid arm and spring rates like the coilers have then the front suspension will be pushed up or compressed by almost an inch or the wheel is actually being lifted by the grip it has on the ground. The more grip, the more the suspension compresses, less grip, the more it unloads. The inch or two the suspension is moving is not changing the relative position of the centre of gravity of the vehicle by any meaningful amount with springs as stiff as standard ones. On buggys and things with 100lb in springs then yes but on a standard vehicle with stiffnesses almost tripple this then nah.

A stage one has a spring rate of 314kg cm (273lb in) The spring would hardly move at all were it to be radius arms instead.

In the case of a leaf spring where both ends are connected to the chassis I dispute that there is any reaction present at all to give jacking or squatting behaviour. Whilst one end is pushing up, the other is pulling down with exactly half the same force as would be applied in a link suspension. Asymmetric leaf springs exist for this very reason. The Land rover with it's symmetrical front springs and vertical shackle position will produce a jacking effect at the front and a squatting effect at the rear of the spring which will balance out exactly the same as an independently sprung vehicle with wishbones. If you imagine the spring to be just a really wide wishbone then you'll see what I mean.

A leaf spring with an unrestrained slipper like what trucks often use but without the restraint instead of a shackle would exhibit the behaviour of a link to some degree but isn't really relevant to the discussion.

PS, I'm not disputing that a hopping / tramping behaviour exists, just that I don't believe it's anything to do with the shackle position but rather a combination of the spring twisting, the damper position behind the axle and the tyre sidewall combining to make the hop, maybe a bit of shaft out of phase with the axle twisting back so a cyclic torque getting fed in, slipping gripping wheel, sticking slipping prop splines and so on. All axles must display some degree of tramp unless rigidly mounted.

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I should also add the difference between parabolic and multileaf where the parabolic behaves as a single fat spring but a multileaf as discussed would have the full spring rate for the front part whether shackle front or eye front and a lower spring rate on the rear part corresponding to three or four leaves depending on construction. This might give a very slight amount of dive/squat but we'd at this point be talking about 20kg or so in the above example so not enough in my opinion to make a difference.

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Interesting discussion Jamie. Don't agree with the shackle end of the spring pulling down with equal force to the fixed end though because it would need to unload the weight that it supports before it can do that,and even then only the 3 top leaves of the spring, retained by the first rebound clamp will be doing the pulling down because the second rebound clamp is a long way from the spring eye. Conversely, the fixed hanger end of the spring, being preloaded by the weight it also supports will more readily lift up the front .All 9 leaves of the spring (my Stage One) are working to lift the front up

I will come back to the thread when I have more time. Meanwhile I just found 2 long abandoned almost complete RRC's on an overgrown bush track on Crown land that require my attention to relieve them of many valuable components. :i-m_so_happy:

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I've come back to this discussion after a few days away to see it has become even more interesting! I do want to add a small observation though. While I understand the theory that having shackles at the front could help reduce the little dance that front axles can do in certain climbing situations, I've seen examples in which it is patently clear that hasn't stopped the phenomenon. One particular case I actually photographed involved a leaf-sprung Land Cruiser climbing a steep and loose hill under full power. The front tramped so violently under the large torque involved that it broke a CV joint (not unheard of!). The result was a very sudden flick to the right and a car tumbling quite alarmingly down the hill. Thankfully the roll cage did its job and the occupants were shaken but okay.

I also wonder if the dynamics of the transmission (amount of and location of free play, any give in the driveshafts) could create a sort of harmonic imbalance at these low frequencies which makes the problem worse? It's what it feels like in my Stage One.

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A quick post before I go back to my Rangey goldmine.

Jamie mentioned attempting an 18" step with both front wheels climbing together. I'd suggest if anyone has a mate with a leaf sprung LandCruiser to go out in the bush with both Landy and Cruiser and find a few banks on the side of the tracks and attempt them at oblique angles. Generally in my experience you will see the Landy front end hopping, skipping and jumping about, with all the attendant clunks and bangs from the transfercase, while the Cruiser, providing the overhang of the longer springs doesn't hang it up, with do a more competent job of conquering the obstacles without all the drama. Another thing ... Take a look at the front shocks on any leaf sprung Landy that sees regular challenging cross country use, and you'll likely see that the shocker bodies are all dented and bashed about from making contact with the swivel housing flanges. That will give some idea of how much these front ends do tramp, and the necessity to address this issue in whatever method, before attempting to gain better articulation.

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Ironically, there seem to be very few leaf-sprung Land Cruisers left! Here in New Zealand, they rusted away in an alarmingly short time. A friend had one for a few years though and, apart from the built-in bulldozer front end (compounded by a P.T.O. winch) which dug into many banks and ditches, it certainly was very competent off-road. He did the "lift and big tyres" thing which possibly helped a bit. Most impressive was when his air intake developed a small leak he didn't know about. The diesel motor hydraulic'd in a deep bog and bent a con-rod. He drove it home anyway!

Debates raged back in the leaf-sprund days about which car was better but the truth was one was better at some things, the other better at other things. It's all a compromise.

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The problem of wheel hop on a series, can IMHO not be ignored. My LWB S3 with 5l V8 and 33" tyres with standard front leafs hopped so badly on a mild hill that it destroyed my front Rover diff. It stripped 6 teeth off the crown wheel. As mentioned in the Jeep article, it is not as simple as running front or rear shackles but also whether you use flat or curved springs in combination.

If I were building exclusively a trail vehicle, I would do front shackles. ( and flat springs in SOA setup)

For a daily driver or overlanding vehicle I would go rear shackles with anti tramp bar.

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And there the conversation come full circle -just fit anti-tramp and don't worry about front or rear shackles.

:)

Not really full circle ! Not as far as the OP's intent of this thread in gaining more flex from the front end . But 'bang for buck', a good antiwrap device wins, and if designed correctly could counter the front end 'jacking' issue.

One more anecdote from me on front shackles. About 40 years ago I met a bloke at an outback fuel stop with a high mileage 1958 Series 1 station wagon . I noted he had done a shackle reversal and I asked him what benefits it gave him. The type of terrain he mainly drove on didn't involve steep mountain goat stuff, but many thousands of miles of flattish corrugations. He told me that he got sick of replacing front propshafts in these conditions because the 'rear ' shackles cause the sliding splines to 'plunge' and wear rapidly, whilst with 'front ' shackles, the sliding joint 'telescopes', and the shaft lasted so very much longer.

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I hate to disagree but I have to chime in again and disagree with what ought to be a common sense argument but my experience is different. I've never changed a front prop on a leafer due to wear on the splines, on the other hand, every single 70 series Toyota Land Cruiser on my last fleet that was over 100k Km's of which would have been about 80 vehicles had an amazing amount of slop in the front prop sliding splines. To the point we actually had to change quite a number. I put it down to religious use of the free wheeling hubs and the props rattling about. That said, a similar sized and aged fleet of Defenders which have the same front suspension didn't display the same wear. Perhaps the turning shaft received better lubrication.

It stands to reason and intuition would certainly dictate that rear shackles should wear a prop spline out faster but maybe the wear is happening over a much larger surface area so is less evident. The constant large movements maybe keeps distributing the grease better.

Another factor potentially against rear mounted shackles would be bind on the front prop splines during times of rapid plunge and high torque like accelerating on rough ground. I cant say for sure I've ever experienced it but it must happen to some degree?

Keeping on track and relevant to the OP I think we all agree some kind of anti tramp bar is a good idea for any long travel leaf spring arrangement with potentially low spring rates regardless of shackle position?

Offsetting it as Bill has suggested in other threads seems like a good idea even on a leaf arrangement. Easier to configure in a rear shackle arrangement.

We agree the original dampers and the original mounts are the reason for the short travel available at the front of a standard Landy leafer?

I disagree about the flat springs and would instead suggest that soft springs with lots of free camber that sit flat at static ride height on level ground will produce more useable wheel travel regardless of shackle position.

I'd also argue that well lubricated multi leaf springs are capable of more travel than parabolic springs due to thinner leaves of the same metal with the same yield point being closer to the neutral axis of each leaf and thus able to bend more before failure. The thicker section of the parabolic certainly does not like to get bent backwards like a multi leaf can.

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One question from a leafer-newbie (that's me)...given the approach angle and the front leafspring mounts being the first to get in contact with an obstacle, what happens with front mounted shackles?

I see the shackle being push backwards, and therefore the axle, correct?

With the stock setup/arrangement instead, maybe the vehicle can be easily (?) pushed forward until tires make contact...does it make sense?

:unsure:

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Pushing the shackle backwards by hitting it directly will result in the spring bending non uniformly with the front part of the spring bending until either the shackle inverts and the spring goes into tension or the spring breaks. By having the flat leaf springs referred to earlier then the spring is able to withstand compressive loads on the end of it better. It's like pushing a bit of bent wire rope and a straight bit. The position of the top shackle bolt is critical. It can be positioned so that the shackle will take some compressive load from the impact directly into the chassis and give maximum swing and travel or it can be the opposite and go into tension almost immediately preserving the spring but reducing wheel travel.

Pushing the wheel backwards by an impact will result in the rear part of the spring with the fixed eye bending until either the shackle at the front goes into tension before the spring breaks or the spring breaks and your transfer case takes the hit via the prop shaft.

The same happens when winching or braking, the forces being smaller just leads to instability, especially combined with a large free camber in the springs.

Herein lies the largest part of the argument. Do you want the instability and lack of axle control whilst braking and hitting things or whilst trying to achieve forward momentum and maintaining traction. Flat leaf springs as suggested earlier get round most of the problems of front shackles whilst maintaining the optimum (for leafs) amount of tractive effort.

It takes a fair old knock to do as I describe the broken spring scenario, in most cases the spring simply bounces and takes the hit with no ill effects. I've broken lots of springs in all kinds of vehicles and find it a fascinating subject.

You are correct that in the stock scenario the vehicle will either push forwards until the wheel makes contact or the vehicle stops (in 99% of situations, so would the front shackles). It's like pulling a bit of rope instead of pushing it. A hard knock breaks the U bolts. Santana U bolts and spring plates are a good upgrade for Land Rovers.

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Eeeh it's all gone terribly technical! A bit much for me as I'm not going to be chopping mine about to make alterations, one must think of originality and all that!

Anyway, I've had a dig through my archives and turned up the contents of the original Gon2far website, so I've uploaded a few things that may be of interest, in no particular order:

88_infield.jpg

bottomshockmount.jpg

coilbeating.jpg

findarock.jpg

gallery1.jpg

gallery2.jpg

p1010133.jpg

p1010136.jpg

parabolic.compressed.jpg

parabolic.xtend.jpg

photo_01.jpg

spring-piv.jpg

spring.xtend.jpg

springpivots.jpg

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I can't comment on the axle tramp issue as I have never experienced it before myself, I guess my mechanical sympathy is a little OCD :)

That spring in the second pic doesn't look too good, I wonder how long it will live when it gets bend like that on a regular basis. I know from experience that the el cheapo parabolic springs from paddocks (presumeably a blue box part...) are able to take a LOT of this sort of punishment without any side effects.

We can make it all a bit more technical and talk about how short springs that arch a lot can have a jacking effect on the chassis when fully articulated as seen in the picture quoted below. This a rear spring which is already a lot longer than a front spring, but look at how steep that angle is from axle to chassis mounting point of the leaf spring. If that wheel has traction it wants to push the axle forwards and is trying to bend the spring and push the chassis upwards. Quite annoying. Longer springs allow for more articulation for a given curvature in the spring.

I've used 63" long chevy rear springs, partly because of this, partly because longer springs are generally softer. The angle from axle to leaf mounting point is not so steep while it has way more articulation.

2012-05-20101124.jpg



p1010136.jpg

parabolic.compressed.jpg

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I agree it doesn't look too great, however Nigel from G2F abused the hell out of both trucks and never to my knowledge broke a spring. He used TIC, and later CPC springs. My truck is running TIC and flex photos show the springs taking the same abuse - although with 37's and portals the springs are working a fair bit harder on rough tracks and (touch wood) nothing has snapped yet.

7s_Flex_Close.jpg

Seems to me there are two threads to this thread - maximising the capability of the "standard" setup, and how far you can take leaf suspension if you are willing/able to make "major" mods like moving chassis mounts, going spring-over, etc.

The Gon2Far kit was bolt-on, with the exception of the front front spring mounts which had to be welded on, albeit keeping the spring eye in the standard position. It retained standard springs in their standard positions, which can avoid legal implications around chassis mods.

Interestingly, Nigel reported that fitting revolver shackles to the front springs made little difference.

Notably although both front & rear have massively longer shocks, I do remember Nigel saying his 1st experiment of unbolting the stock shocks & ramping the truck made nowhere near as much difference as he'd hoped.

I don't know if anyone rescued tech threads from the "old" forum (LRE as this place was a million years ago!) as there was a lot of discussion on it back in the day.

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