Axle wrap/tramp control

[Snagger]

I have found the source of the nasty noise that occurs under heavy braking of my Tdi powered, Defender axled 109. I had thought it was brake judder or even the tyres slipping n the rims, but no, it's the front UJ rubbing against the rhs engine mount bracket. The combination of nose dip and axle wrap causes the diff nose and front end of the prop shaft to move up, and given that the starting position is relatively high because of the axle swap and the Defender 200Tdi engine mount sits a lot lower on a Series vehicle than in a Defender, the combination is too small a clearance, even with my three-leaf parabolics and 1Ton chassis and shackles.

So, part of the solution is to modify the bracket - luckily, I have a Discovery engine with Defender manifolds, so have plenty of space under the injection pump to move the span of the bracket upwards. The other part of the solution will be to look at controlling the amount of axle wrap. I am considering a very simple pair of arms that will connect from the axle bump stop pads to the rear spring eye bolts, forming a stable triangle. The straightening of the spring under compression will result in that side of the triangle lengthening, while the vertical and top sides of the triangle (the axle case and the anti wrap bars, respectively) will be constant, which will cause a small amount of axle rotation with the diff nose moving down under spring compression, but I think the effect should be small. Connecting similar rods to the front spring bolts would cause the diff nose to pivot up under spring compression, but would also foul the steering system's drag link. What I have in mind is a pair of scrap coiler trailing arms with the cylindrical bush fitted in a bracket welded to the axle and a new end fitted in place of the stud end that would attach to the spring bolt. Any opinions?

Word of advice for those considering such mods - 12J/19J?Def200Tdi and coiler axles don't mix unless you come up with an engine mount that goes over the top of the injection pump. You can fit a Discovery 200Tdi or 300Tdi with coiler axles because of the higher injection pump. However, with parabolics greater wrap, and especially with standard mountings and two leafs, you're going to have to watch the separation of the diff nose and engine mount/injection pump under heavy articulation and braking.

[lexi]

It will be suck it and see I think for the way it will perform. Sounds feasible. Other than stiffer springs or an extra leaf.

The engine bracket cannot be modified?

[Daan]

I think the arms going backwards would still cause the diff to rotate up, because the axle moves backwards when it moves up (with shackles at the back). I would go for a single arm from the top of the diff going forward to the front crossmember, forming a paralellogram with the springs.

Daan

[ian_s]

isnt this exactly what Soren has done here?

http://forums.lr4x4.com/index.php?showtopic=26822&p=709273

[Daan]

hmm, reading this again, it looks like sorens solution. I had the impression from the first time I read it, that you wanted to connect to the chassis bush were the shackle goes through.

The problem with sorens solution is axle wrap: you force the axle to rotate around the rear springbolt, causing the front part of the leafspring to bend a lot and the rear part of the spring not at all. Plus a lot of axle rotation.

Daan

[Tanuki]

You're suffering from the classic 'compromise' that arises when you try to use a leaf-spring as a suspension-medium and an axle-locator at the same time.

My thought would be to switch to using something like "hockey-sticks" and a Panhard-rod (as used on coil-sprung LRs) to locate the axle with respect to the chassis, then grind the 'loop' parts off the ends of the leaf-springs at both ends and fit a roller- or slipper-type arrangement to handle the longitudinal length-change as the spring compresses and releases.

This is exactly what we did on the 1970s/1980s-era Ford Escort rally-cars: have a look at http://www.rallyanarchy.com/EscortRallyPrep/Suspension%20Rear.pdf for details. This positively locates the axle and completely removes the springs from doing anything except handling the up-and-down stuff.

[Snagger]

I'd be interested in seeing how Soren connected the axle end of the control bar, but that is the principle I had in mind. It should work pretty well - when applying lots of driving power, the bar would be in compression, an when braking hard, it would be in tension. It wouldn't take any bending forces. By forming a triangle between the rear of the spring and the top and bottom of the axle, it should be pretty stable - triangles are the most stable shape you can get and are used extensively for structural systems because of that. A small amount of axle movement would still be imparted, but only from the spring side of said triangle lengthening as the spring is compressed and straightened. This would rotate the diff downwards, not up, as the apex of the triangle is floating with the axle by being on the spring eye - if it was on the chassis eye, it would rotate the diff up just as your suggest.

I had been toying with the possibility of fitting the system atop the front of the spring, perhaps using the upper spring bolt holes in the 1-Ton chassis, but I suspect the spring eyes obstruct the hole and I think the drag link may foul control rods in that position.

As for the Willys solution, that is also an option, but that's putting all the forces through the U-bolts and is still relying on the stiffness of those bottom members, so they need to be really heavy. Forming a triangle seems more elegant and avoids the extra U-bolt loads as the anti-wrap forces would be transmitted directly along the control arms in compression or tension. Only the rear spring bolt would carry etra loadings, and that would only be outboard of the shackles, so shouldn't shear the bolt.

[Snagger]

It will be suck it and see I think for the way it will perform. Sounds feasible. Other than stiffer springs or an extra leaf.

The engine bracket cannot be modified?

As I said in the first post, the first part of the solution is to make a new mount, which I can get away with because I have a Discovery engine giving me that space, and I already have a third leaf on the parabolics, all from Heystee, The oly way of stiffening the springs would be to ho to very heavy duty standard leaf springs, byt even that won't achieve a great deal.

[Soren Frimodt]

What Daan suggested in post #3 is exactly what I've done on my 80" and it works really well, nothing binds and nothing gets worn out prematurely. So if you could find the room for that, I think you shoul really do it. The way I've done it on 88" now is only a quick setup. It does seem to do the job just fine today though, but dunno how long the bushes will last.

[Snagger]

Thanks guys. Food for thought. I like Soren's solution as it doesn't put strain on the chassis cross member, which wasn't designed for those forces, and avoids any contact with the sump or pulleys. I use Polybushes in my springs, so they should take the forces without much complaint and will be easy to swap if they don;t cope. I think I'll go that way first and see how things go - I can always change later. I'm not keen on the Willy's set up - my springs have too much camber anyway, but it puts a hell of a strain on those U bolts.

[Gremlin]

I was going to make an anti tramp bar when i did the rebuild, sadly i never did it. I still have all the bits, so someday it will be done.

My plan was to run from the axle towards the front, out to the bumper, making it as long as the possible. I was going to use a rear coiler trailing arm, cut down to size with a doughnut style mount (like coiler fronts chassis raduis arms) Although rather bulky, i also got a johnny joint and a rose joint just to see what will work best in the space available.

The only reason i was going to make mine was due to axle tramp while climbing steep hills, the front axle has a bad habit of hopping around.

Braking was never a problem even with the disc brakes, although when i slam the brakes in reverse the springs do funny things (feels like axle wants to come out from under the car!)

G

[Gareth Dickens]

I'm looking at something similar. I had to cut up a defender front axle to graft the flanges to my Salisbury axle and so have the radius arm brackets from the axle and was thinking of using the radius arms to do a anti wrap ladder bar. They are just so heavy. They do seem like the easiest solution though. Maybe one can grind them a bit thinner?

Are they weld able? I was thinking to cut them shorter and then fit a rose joint to far side (away from the axle).

I was looking at going aft from the front axle though, to the semi v shaped cross member (by the bell housing) and from the rear axle forward to the cross member just fwd of the rear spring fwd hangers.

What do you think?

[bill van snorkle]

Not an original idea of mine, but how about a shortened single radius arm, mounted wherever it's convenient on the axle,with a cylindrical bush unit welded to the chassis end of the arm and running back to a swinging shackle mounted off the crossmember under the bell housing ? With stiff poly bushings at the axle end this would provide wrap control, but the shackle will still allow the axle to move back or forth as the leaf springs flatten and rebound.

There may be enough compliance in the original 2 piece donut bushings to accomodate the changing length of the spring as it flattens, thus not requiring a swinging shackle.

Radius arms are forged steel and are very malleable and weldable.

[Snagger]

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

No solution is perfect, but I still think the "Soren bar" is the most practical and elegant in this scenario. I'll try that first and see if the bushes take it.

!N

[dirtydiesel]

There's plenty of decent kit out there to copy such as,

http://www.americanfourwheeler.com/WFO-Heavy-Duty-Torque-Arm-Anti-Spring-Wrap-Bar-Kits.html

[bill van snorkle]

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

No solution is perfect, but I still think the "Soren bar" is the most practical and elegant in this scenario. I'll try that first and see if the bushes take it.

!N

Running a radius type arm (with 2 bushings at the axle end) rearwards could give other benefits when climbing in that the torque reaction from the front axle could neutralise the normal leaf sprung LandRover tendency to 'jack' the front of the vehicle on steep climbs. To explain, if you can visualise the front half of the springs as being a type of short radius arm. As the axle housing tries to roll backwards due to torque reaction,, this force pushes the front of the springs and nose of the vehicle upwards. Of course the back half of the springs also get pulled downwards, but this only serves to unload that half of the springs and generally doesn't tend to pull the chassis downwards like radius arms or springs with front hung shackles do as on Jeeps, LandCruisers etc do.

[Gareth Dickens]

I was going to make an anti tramp bar when i did the rebuild, sadly i never did it. I still have all the bits, so someday it will be done.

My plan was to run from the axle towards the front, out to the bumper, making it as long as the possible.

G

I believe that there is only one solution, and that is a ladder bar attached to the chassis via a swinging shackle. A radius arm effectively is a ladder bar. A single rod as per Soren will cause spring deformation and relies on the rigidity of the leafs to form a force triangle to counter the wrap effect. As soon as you fit softer leafs (parabolics)you lose the strength of the triangle and can in fact worsen the wrap.

As for the direction of the ladder bars, I believe the fwd axle ladder bar should attach aft of the axle and the rear axle ladder bar should attach fwd of the axle. As per Bill's explanation under braking the chassis will be pushed up in front and pulled down at the back, thus fighting nose dive. During pull off or climbing the front of the vehicle will be pulled down and the back raised countering the natural tendancy of the rear leafs to compress and the fronts to extend. Whether the force applied by the ladder bars is large enough to negate the spring compression, I do not know and I do not think so, but rather a force in the opposite direction than one working with the spring compression.

[bill van snorkle]

To add to Gareths explaination. A radius arm or ladder bar attached to the chassis via a swinging shackle can be as short or as long, within reason as you want to make it, but the shorter it is, the greater up or down force it can apply to the chassis.

[Snagger]

With the amount of spring distortion I must be getting to suffer the prop impacts that are occurring, the springs must be pronouncedly "S" shaped under heavy braking. There is no way that the Soren bar is going to worsen things and no way that the spring will distort more due to longitudinal compression over its arced length. The ladder bar may be more effective though, and won't place extra loads on the rear spring bolts or bushes (though the Soren bar may alleviate bush loadings because of the reduced rotation of the spring eye from preventing the S-bending). I'll have a closer look at the feasibility of a forward bar connecting to the front (steering relay) cross member once I have sorted the gear box and engine mounting.

[Daan]

problem with the ladder bar is that the S shaping of the springs is happening all the time while cycling through the suspension travel. You force the axle to rotate around one point, were as the natural movement of the axle is just up and down. I believe the ladder idea is therefore fundamentally flawed, regardless of how many people are using it. That front crossmember will easily take the loads of a toplink, as long as it is sound.

Daan

[Gremlin]

My choice of going with the single link on top of the axle, slightly off center, is simplicity, but going to the front standard series x member might make it a tad too short, making some nasty arcs which might not help in reducing stresses on the link itself. I once had this discussion with you Bill on this.

I have an extra x member just in line with the bumper mount points, and i was going to go out with the bar to this location making it as long as half the leaf spring, so it will theoretically move in sort of paralell to the front of the spring, although the springs bend and get a fraction longer as they get straighter/flatter. My solution to see if this will work was going to be to mount my axle on a single main leaf and cycle it in the garage and see what is actually happening to the suspension and spring geometry. The xmember mount would be rubber doughnut hopefully will be complient enough to allow the minor chages in lenght of the spring and it cycles trough its travel.

The theory behind the traction part of it while offroad might not be right but it will hopefully stop the axle from hopping around while it unloads. Running it to the rear x member seems a bit complicated with lots of parts, rods, shackles, and bushes to see to.

Sadly finding the time to pull the landy off the road for such experiments has become a no, no, as its a daily work vehicle, and i do not have another run around. So this project has been put on the back burner, but some day i will get back to it.

G

[bill van snorkle]

problem with the ladder bar is that the S shaping of the springs is happening all the time while cycling through the suspension travel. You force the axle to rotate around one point, were as the natural movement of the axle is just up and down. I believe the ladder idea is therefore fundamentally flawed, regardless of how many people are using it. That front crossmember will easily take the loads of a toplink, as long as it is sound.

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.

Gremlin. There is nothing wrong with the description of the link you want to make. I did one like that on a friends stage one with a 4.6v8 and 36'' TSL's that previously used to regularly break front springs, propshafts and shocks. The link completely eliminated those issues and transformed the vehicles offroad capabilities.

I'm just trying to introduce a bit of antisquat/antidive science into the equation with the radius arm/swinging shackle principle.

[discomikey]

heres a thought, while it may take up space and a fair bit of engineering, whilst also affecting spring rate, is there a possibility of mounting a single spring leaf, on the top of the axle, with the front eye and rear swing shackle in paralell with the road springs, this would give an anti wrap effect, whilst also not altering the diff nose angle at any point in bump travel. Although i havent thought it through and just came up with it on the spot so may not actually work, its an idea at least.

[bill van snorkle]

There's plenty of decent kit out there to copy such as,

http://www.americanfourwheeler.com/WFO-Heavy-Duty-Torque-Arm-Anti-Spring-Wrap-Bar-Kits.html

The advantage of a Rangerover radius arm over the above, is that the bushings are more or less horizontally displaced, so engine sump pulley clearance shouldn't present any problems. The other fact that the radius arms already exist and together with an old bent trailing arm (for the shackle bushings) can often be picked up for free is another plus.

[Snagger]

I've had a quick peek around the front just now. There is no way that a link to the front cross member would work satisfactorily, shackled or not; it's just too short a gap and would result in a different set of wrap forces, rather than controlling the existing forces. What does look potentially feasible is a pair of rods connected by transverse bolts and bushings (I'm thinking of coiler trailing arms) to the axle, just outboard of the U-bolts, and rose (Heim) joints at the front end, bolted to the outside of the dumb irons through the upper spring bolt holes, the bolt of which will just clear the spring eyes inside the dumb irons.

This will give rigid thrust arms to sold chassis mountings with free rotational movement for cross-axle motion and free pitch movement at each end of both rods for spring compression, but fixed length roughly parallel to the springs for anti-wrap control. It won't impinge on the spring bushes, will maintain the same axle axis at all suspension ranges and while being outboard of the springs, won't impinge on steering lock because they will be forward of the axle, where wheel/tyre steering motion is less at full lock (as it is the turn's outboard, lesser pivoting wheel that moves towards the front of the spring). I should even be able to buy off-the shelf brackets from YRM... I need to take a close look at the possibility of fouling the drag link on the near side, but that looks unlikley.