Axle wrap/tramp control

[Gremlin]

There is no need to go with trailing links from a coiler if you are using 2 rods. I would use somrthing smaller which would help with packaging the links.

Have a look at a hilux with a solid front axle, they had 1 link on top of the axle to get an idea of size. Go to a scrap yard and rummage under some modern cars, they all have some sort of links which may be very usable for what you want to do. Some even come with rose joints with rubber caps and adjustable! I have one from a toyota of unknown origin, which i have been saving for this purpose.

G

[Soren Frimodt]

Sorry guys, but I really think some of you are making rocket science out of a spoon!

These two pictures show how I've done mine on my 80" and it really does work! No binding or premature wear on anything and the joints themselves see a dab of oil a couple of times a year and still work as if they were new!

The only real "tech" is that I've made the distance from the two joints exactly the same as on the spring from center axle to center chassis-bush, and the height as well so it runs parallel to the spring.

[dirtydiesel]

Sorry Soren but,

You need to resist buying another leaky rust bucket and treat yourself to a tube bender!

[Soren Frimodt]

Haha I do have a tube bender, even one that could bend this tube. But because I knew I had to reinforce it heavily at the kink (which shouldn't be there at the first place but had to because of my steering ram) bending instead of cutting would make no sence. I've slid another tube in there at the kink for greater wall thickness so had to cut it anyways. You guys don't need this kink, so don't go restless because of it please! I did it on my 88" without the kink.

[bill van snorkle]

Whilst Soren and others have had satisfactory results with a single bar without compliant bushings running forward and,I am probably being a bit anal here, but it is really quite wrong from an engineering viewpoint. Whilst it probably works well enough for single wheel bumps, where the spring on the bump side can still move back and forward as it flattens and rebounds, for situations such as corrugations, where both front wheels strike bumps at the same time repeatedly thousands of times over significant distances like we have here in OZ, I can see the rose joints having a fairly short life, as well as cracked axle casing/crossmember or the mountings themselves, not to mention a relatively short life for the springs main leaves, The bar should have at least some compliance in the bushings to allow both springs to flatten and rebound (cycle) simultaneously without distortion. The only way to insure that, is to disconnect one end of the tramp bar, load up or ratchet down the chassis so that both bump stops are sitting on the axle. Then see if you can reconnect the tramp rod.If you can't and the bolt holes in the mount and the bushing are misaligned by significantly more than the bushing compliance can accomodate, then you need to add more compliant bushings, otherwise something somewhere is being strained.

The problem with compliant bushings is that they will still permit a degree or three of axle wrap/tramp, and this is where the radius type arm with swinging shackle is once again superior, in that you can have completely solid bushings at the axle end.

[FridgeFreezer]

That sounds similar in principle to what Fridge did on his rear axle. I am still hoping he'll contribute to this thread!

OK then

TBH I'm not sure what I can contribute, my anti-wrap is already documented on here, still works, I haven't touched it other than to notch the front x-member for the P38 sump. I still think my front arm is too short but I haven't really had time to re-think it - despite TSD creating an excel spreadsheet that accurately calculates the movement of a leaf spring and draws a picture of it so that I'd stop talking about it I can probably e-mail a copy to anyone who's interested enough.

I'm also with Bill - the single-bar approach may be "ok" or better than nothing, but it's not correct when you account for the movement of the spring and is probably forcing things to move in a way they don't quite want to.

[Soren Frimodt]

Wise word from both of you, and I can see what you mean. But as you say John, a single bar is better than none, and it really is. My very scientific way of testing mine was to go onto the tarmac, build some revs and drop the clutch! This resultet in instant wheelspin and no other dramas whereas when I did it without the bar the car would almost launch itself to the moon because of the grip and wrapping of the springs. With regards to bushes the one bar version could easily have one or two, but as bill says it will introduce some hopping issues again. Just look at the front end of a coiler, it bounches almost as badly a leafspring.

[Snagger]

That compliance issue is why I want to use something with bushes at the back. I have a pair of old front spring plates, so could attach them to the top of the bump stops and use their damper mountings and a pair of 109 Ambulance rear anti-roll bar links for the control arms, with standard damper bushes. With these arms running roughly parallel to the front halves of the springs, they shouldn't need to allow too much compliance and the damper bushes should easily suffice. As for the fact that this would still permit a small amount of wrap, well so do the bushes in coilers' radius arms up front and the trailing arms and front of the A-frame at their rear. A small amount of wrap isn't an issue - this is no comp-safari racer or rock crawler; I just want to prevent damage to the suspension and steering.

[Daan]

I don't agree Daan.I believe your thinking is discounting the swinging shackle. The ladder bar or radiuus arm with swinging shackle isn't forcing the axle to do anything. Torque reaction is forcing the axle housing to rotate around the axle shafts. The ladder bar/RA is merely resisting that rotation. The natural movement of the axle with arched springs is actually up and rearward, down and forward, and that is what the swinging shackle will accomodate.

I am not discounting the shackle, the shackle will allow movement of the axle backwards and forwards, with a slight up and down movement as a result.

But the ladder is cannot move up and own. It can only rotate around the shackle mounted bush, rotating the axle with it. While this does give it the anti dive/tramp forces you are mentioning, it introduces a lot of springwrap, which was what we were trying to get away from.

Daan

[Snagger]

I am not discounting the shackle, the shackle will allow movement of the axle backwards and forwards, with a slight up and down movement as a result.

But the ladder is cannot move up and own. It can only rotate around the shackle mounted bush, rotating the axle with it. While this does give it the anti dive/tramp forces you are mentioning, it introduces a lot of springwrap, which was what we were trying to get away from.

Daan

That's what I was thinking - it prevents axle wrap from torque reactions, but induces wrap with axle articulation, making the exercise pointless and putting stresses on a cross member not designed with those loadings in mind. The "Soren bar", as per his 88", is a much better solution. I'll try to fabricate the parallel bars first, though.

[bill van snorkle]

Daan/Snagger. IMO you are still misunderstanding that a radius arm attached to the chassis via a swinging shackle has 2 pivot points not one, so it is the springs themselves that dictate the arc that the radius arm moves up and down in, not the other way around. The shackle adjusts the position of the radius arm pivot point so as not to distort the springs.

As for the radius arm bushings on coilers allowing for a degree of wrap, that is very true. But if Rover had elected to mount the dampers on brackets either rearwards or forward (as on air susp models)of the axle centre instead of directly on top, wrap could have better been controlled.

Fridge, when you state that you think your tramp bar is too short, Is it because you feel that you are experiencing too much offcentre antidive?

Gremlin, I'll have to check with my neighbors Hilux, but from memory, they are a little different to LandRovers in that they are spring over axle and the front springs have very little arch (camber), so the up and down movement of the axle is more vertical vs up and back, down and forward for Landys.That is why I think hiluxes get away with a single tramp rod, and also why when Hiluxes are fitted with aftermarket high arch springs the tramp bar is generally removed, because it causes similar issues to what we are discussing here, in addition to bump steer due to the for/aft orientation of the steering draglink. The other point to consider with spring over axle is that the vertical separation between the axle centreline and the main leaves is greater than for spring under, and the vertical separation between the main leaf and tramp rod bracket is less than what we are discussing with LandRovers, so tramp dynamics may also be quite different, but I have to go to work now so I can't think about it much at this time.

[FridgeFreezer]

Fridge, when you state that you think your tramp bar is too short, Is it because you feel that you are experiencing too much offcentre antidive?

Not quite that scientific Bill - it's because it's about half the length of half the spring, to me that makes the geometry look all wrong, intuition says it should be about the same length as half the spring with a similarly proportioned shackle.

It may well be that my intuition is wrong, but overall I can't quite shake the feeling that the most elegant solution to this problem has not yet been arrived at. I can't say I've been able to pinpoint anything wrong with the performance of the front, but then without strapping a camera under there it's hard to tell what's really going on.

The rear I'm entirely happy with as the bar points forward and ends at about the same place as the spring eye, so that looks right to me and it certainly seems to behave right. It does have the advantage of the stiffer / thicker rear springs and being a longer bar it has mechanical advantage on its side too.

As an aside, it has also confirmed my suspicions about heim joints in UK offroading conditions, the ones fitted are by no means cheap and I wouldn't fancy them on my steering system given how quickly they get loose. In their current application it doesn't really matter, and I've not bothered changing them as they're not rattling around... but they are definitely not tight any more.

[bill van snorkle]

Not quite that scientific Bill - it's because it's about half the length of half the spring, to me that makes the geometry look all wrong, intuition says it should be about the same length as half the spring with a similarly proportioned shackle.

It may well be that my intuition is wrong, but overall I can't quite shake the feeling that the most elegant solution to this problem has not yet been arrived at. I can't say I've been able to pinpoint anything wrong with the performance of the front, but then without strapping a camera under there it's hard to tell what's really going on.

The rear I'm entirely happy with as the bar points forward and ends at about the same place as the spring eye, so that looks right to me and it certainly seems to behave right. It does have the advantage of the stiffer / thicker rear springs and being a longer bar it has mechanical advantage on its side too.

As an aside, it has also confirmed my suspicions about heim joints in UK offroading conditions, the ones fitted are by no means cheap and I wouldn't fancy them on my steering system given how quickly they get loose. In their current application it doesn't really matter, and I've not bothered changing them as they're not rattling around... but they are definitely not tight any more.

Fridge, My experience with parabolics, in the form of early Transit front springs, fitted to the rear of my pure bred mongrel, is that they are more brittle than conventional leaf springs, and are not very tolerant of tramp rods or control arms with conflicting geometry to what the springs want to do when they flex. The fact that your front shackle type radius arm, despite being so short, works well and hasn't caused you any broken springs IMHO disproves Daan and Snaggers concerns that this type of wrap control has a detrimental affect on springs.

As I suggested on an earlier post,a short front radius arm should give a stronger antidive effect when braking and more front squat when pulling or climbing.Have you noticed with your offset control arm that the front of your vehicle tilts more to one side under brakes?

Heim joints are illegal on the suspension or steering of road registered vehicles in Australia. A dirt track circuit racer once told me that 'you can't win with heims' Don't grease them and they wear out quick. Grease them and dust sticks to the grease, forming a grinding paste and the heims wear out quicker.May be best to grease them, and slide and cable tie a condom over them before bolting them up to keep some of the muck out.

[FridgeFreezer]

There are a few extra factors here;

- I drive like a pussy off-road

- My springs are original TIC's which are about the most robust paras anyway, they stand being bent backwards etc. quite happily (back in the days of Gon2Far Nigel was doing this abuse to them all the time!)

- With 37's and portals and a V8 and PAS and a roll cage it's hard to form any sort of opinion on what the truck should handle like.

I suppose the argument that "it's not broken so it's probably working" is given some credence given the overland abuse my truck has taken compared to many weekend toys.

I'd still like to prove the theory with engineering before declaring it The Right Answer.

[Gareth Dickens]

I have to go with Bill and Fridge on this one. I had the same conversation with some fellow 4x4'ers at work and also had to convince them that the ladder bar/ radius arm will not induce wrap in the springs because of the swinging shackle.

A few things I have convinced myself to be true, but have no proof of, is :

1) I believe the tramp bar shackle should be at least the same length (if not longer) than the spring shackles.

2) The shackle angle should be the same or a bit further swung when compressed than the spring shackle.

3) point 1 and 2 are so the tramp bar does not limit axle down travel

4) the tramp bar and shackle should be as close to the centerline of the chassis as posible.

5) the tramp bar should be half the spring length. (mostly to keep things simple)

6) the front axle tramp bar should run aft and the rear axle tramp bar should run forward.(fo reasons discussed before)

7) The lower bar of a ladder bar (or only bar of a radius arm) should intersect a line between the spring hanger bolts. (mostly for break over angle)

Most of these are gut feel because of some reasoning, but things like the optimal length of the tramp bars to counter nose dive during braking and lift during acceleration is beyond my mathematical capability and patience level.

[Snagger]

I'm not that up to speed on suspension mods, despite reading an American book all about it. The thing is, while a lot of after-market suspension kit well designed and built, a lot is clearly inappropriate and ill-conceived - the book showed leaf springs so arched they were semi-circular, which would make them almost totally rigid in compression but wobbly laterally, heavily sloping panhard rods that would induce heavy bump steer and cranked drag links that would not just cause bump steer but also be prone to flexing at the bends. Also featured in the book were the ladder/shackle systems you guys are advocating, so I understand their concept, if not their exact operation.

Now, these may work a treat, but I have this concern - fitted with the shackle vertical or, presumably, parallel to the spring shackles, they will permit the fore/aft travel of the axle caused by leaf spring compression while eliminating axle wrap from wheel torque reaction. That much is clear. But, while the longitudinal motion of the axle would be accommodated by said shackle, I can't see how vertical axle movement would be; it appears to me that axle movement towards the chassis would cause the shackle and ladder to apply strong wrap loads on the axle. So, while gentle cross-axling would not cause wrap as long as the ladder was mounted centrally, any bumps that compress both springs simultaneously would wrap the axle. The only way to avoid that would be to incline the shackle on a wide obtuse angle with the rod or ladder, but that would make its wrap control weak...

If anyone knows of any diagrams or videos which explain how these systems work, so that my concerns can be allayed, then please post them up. It looks like a big enough job that I want to get it right first time, and getting it wrong could have big consequences.

For what it's worth, my springs are TIC, like Fridge's, and I doubt anyone could level an accusation of fragility at them.

[Gareth Dickens]

I agree that if the shackle were to be perfectly vertical it would want to push the tramp bar down. Therefore it's a case of setup, similarly to making sure that your leaf shackles are over center with the vehicles weight on the axles, but ensuring they do not swing so far as to colapse. It's a case of correct suspension geometry. Still there is no perfect solution when it comes to leaf sprung suspension , but picking the lessor of two evils, I would still advocate the ladder bar over the solid bar. When doing this mod, I sugest the radius arm should not be horizontal (up at 30-45 degrees) and the radius arm shackle should be at close to perpendicular to the radius arm (not the chassis). This will control rotation of the axle, but allow up and down, forward and aft movement of the axle and by using a rose joint or tie rod end somewhere between the tramp bar and shackle will allow articulation as well.

Correct me if I'm wrong, but prove it.

[Snagger]

Ah, that makes sense now! I thought the ladder was horizontal, with the shackle roughly vertical but that inclination would allow the vertical movement of the axle while retaining the essential 90 degree angle with the shackle. Still, that's going to be difficult to fit at that angle without running from the front lower face of the axle case, through the drag link area - mounting it higher would mean running it awfully close to the engine crank pulley. It's an odd dichotomy of leaf springs - simple in principle and installation, but a git to modify to eliminate its few weaknesses.

[bill van snorkle]

Ah, that makes sense now! I thought the ladder was horizontal, with the shackle roughly vertical but that inclination would allow the vertical movement of the axle while retaining the essential 90 degree angle with the shackle. Still, that's going to be difficult to fit at that angle without running from the front lower face of the axle case, through the drag link area - mounting it higher would mean running it awfully close to the engine crank pulley. It's an odd dichotomy of leaf springs - simple in principle and installation, but a git to modify to eliminate its few weaknesses.

Once again, the shackled tramp bar should run aft of the axle to the bell housing crossmember, so that steering linkage is not an issue, unless you are using a coiler axle that is. Also, and I apologise but once again,a coiler radius arm with their more horizontally displaced bushings, and fitted roughly mid axle, shouldn't present clearance issues with the engine components.

Another thing to keep in mind is that LandRovers have very short leaf springs, so we are only talking about a comparatively few inches of suspension travel, so it is easy to overthink stuff like arcs of movement and arm lengths when discussing shackled controll arms. Fridges ulta short example is testament to that.

[Snagger]

Like I said in the first post, Bill, this whole problem has come about by fitting a coiler axle on leafs - it's the raised diff nose that's the problem, striking the engine mount. I don't know if the old drum braked axle had the same amount of wrap - it wasn't something I'd ever looked into, but given that I was able to easily lock those brakes on a dry surface, the maximum level of braking and therefore torque reaction on the axle may have been comparable. In that case, I might even be "overthinking" the whole issue by fitting any anti-wrap system at all - the springs have lasted a hell of a long time and mileage with no ill-effect so far, so perhaps just sorting the engine mount will be enough by itself? Even if the disc brakes do create more torque than the drums could, by adding the third leaf and 50% spring rate at the same time as fitting the axle, then there should be little trouble. I just get uncomfortable envisaging stresses and component deformation!

[bill van snorkle]

Snagger,Coil axle diffs are tilted up around 12 degrees further than series leaf axles. If you were doing the axle conversion from scratch, you should probably weld the leaf spring saddles so that the pinion is parrallel with the road as on a leafers. I'm not sure if 12 degrees would allow you to drill a fresh set of bolt holes in the swivel ball flanges, but even if you had to slot the original holes you will restore your castor angle. Two fresh bolt holes in both the axle housing and swivel balls will address fears of the balls rotating around the slotted holes.

To get some idea of how much spring wrap an unmodified series vehicle can get, take a look at one that is used regularly in proper cross country terrain and you should see where the lower part of the front shock absorbers have been severely bashed by the swivel flanges. I've had LWB shockers due to their larger diameter so badly dented that the inner working cylinder has been damaged and the unit has seized.

No doubt some will opine as on a similar topic a while back, that slotting the bolt holes will weaken the swivel ball flanges, but that fear can be addressed by using longer bolts and specially shaped washers, or even a whole other flange cut in half.

[Snagger]

You can't set the diff level, Bill - the track rod will be passing through the diff nose area. The position of the track rod causes a lot of problems when fitting later axles to leaf suspension, and I'm not willing to use a forward track rod because I really don't believe screwing up the Ackerman angles is a good idea. I got it all to work, except for this unexpected prop contact. From what you say, the wrap that I get under heavy braking is normal, regardless of which type of axle is fitted to this suspension, so won't have any worse implications for the service life of my springs or steering components, suggesting that I may have been right in my speculation that an anti-wrap system is not actually necessary, though it would be beneficial.

As for slotted bolt holes in flanges - they would certainly weaken the flange, but if I was to re-orientate the swivels, I'd weld the holes up and re-drill in the new positions.

[bill van snorkle]

You can't set the diff level, Bill - the track rod will be passing through the diff nose area. .

Yes, I was in a hurry to go out when I typed my last post this morning, and I forgot to include that a lot of 4wd trucks have the trackrod behind the axle also, but the trackrod is usually formed into a cow belly shape to clear the bottom of the diff nose. I was thinking for your arrangement, cosidering that the trackrod sits above the leaf springs anyway, that the cowbelly would be above the horizontal diff.

Whilst your summising that the degree of axle wrap you are getting is normal for a leaf sprung LandRover is probably correct it is still something that is desirable for all the reasons that have been discussed, and wouldn't you desire to to control axle wrap anyways?

[Snagger]

I'd prefer to stop it, but it sounds like it'll be preferable rather than essential, and so is less urgent, and if it gets a bit difficult, then less of a worry if I have to drop it. My first job is to rebuild the gear box - I got it stripped down today, and thankfully it's just the third gear wheel on the main shaft and the big bush on which it sits that are damaged, with all the other components being unmarked, and I already had a gen parts new third gear wheel in my spares box, so once I get the new bush, I'll put all that back together. I can't sort the engine mount out, which will be the next job, until the transmission is refitted and setting the engine alignment correctly. Hopefully, barring any other disasters, I'll be able to do something about the wrap after that.

I did look at the possibility of a cranked track rod and level diff, Bill, a bit like on the 101, but it wasn't possible - the diff is too close to the rhs spring, so the section of rod dropped to clear the diff on right lock would severely foul the spring on left lock. I spent two years fiddling and assessing how best to fit a RR/Def?Disco front axle before doing it, and I think I got a pretty damned good solution, but overlooked this engine mount, which is only a problem because of the previous engine conversion using the low down 12J-200Tdi mount. It probably wouldn't have been a problem with a SIII or Discovery mount.

Thanks for all your input, everyone.

[bill van snorkle]

Off topic. but a tip on your gearbox fix. If the bronze bushing is just broken in 2 pieces. but the broken ends fit together like jig saw puzzle pieces, then it can be re used, and is actually preferable to fitting a new one piece bush. Rover engineers,after over 40 years of that type of gearbox being in production, finally realized that bronze bush breakage was due to mainshaft flex, and replacement bushings were made as 2 piece units. Whether you choose to reuse the old bushing or to fit a new 2 piece one, do make sure to stake the front half into one of the mainsshaft splines to prevent it from spinning on the shaft.