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Disc brakes and parrabolics


MECCANO
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I was jsut wondering, has any one else suffered any problems from using parrabolic leaf springs and also upgrading to discs.

I have noticed a slight distortion in the paras shape ( although this may also occur on drums). As well as suffering from alot of spring wrap under heavy braking.

I'm considering returning to stock springs, as an easy alternative to fitting some form of anti wrap/ traction bar.

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Well in a way you just answered your own question there mate ;) Yes it IS a problem with effective brakes and parabolics, as well as big horsepower and parabolics is. So either go standard spring, or make an anti wrap bar. On my new project I'm going to stay standard multileaf spring, should solve a lot of problems, and as always there must be a reason why it's made that way from the factory. Sure there where advantages to the para's, especially better flex and more groundclearance.

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yep, got the same problem here. range rover axles on parabolics and ive experienced bad spring wrap under braking and offroad with the v8.

unfortunately i had it with standard springs so have just decided to live with it as theres no easy way to fix it.

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It might just be me, but i find it pretty appauling that they really arent fit for purpose.

I'm going to look into anti wrap bars. Possibly similar to Sorens setup just to firm things up a bit and stop the diff pitching up.

A full ladder is just going to be to difficult to achieve up front.

If all else fails, its back to multi leaves.

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It might just be me, but i find it pretty appauling that they really arent fit for purpose.

I'm going to look into anti wrap bars. Possibly similar to Sorens setup just to firm things up a bit and stop the diff pitching up.

A full ladder is just going to be to difficult to achieve up front.

If all else fails, its back to multi leaves.

So what we want is some really soft springs that are hard at the same time, designed for a 2 1/4 on 6.50s and drums but running 200tdi or v8 through simex a likes?

Would a set of soft saggy wornout multi leaf springs resist wrap better than a good knick parabolic? If so add a coilover to bring spring rate back and see what happens. Series leaf travel length coilovers probably aren't that expensive...

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Exactly Rob, you hit the nail on its head there! ;) But I think the main reason that multileafs cope better with axlewrap is because of the much higher friction between all the leafs.

I suspect it's more to do with the overall thickness of steel near the axle and the tapered nature of the leaf stacks.

Two-leaf parabolics do seem to have trouble with V8s and Tdis. I have 4-leaf rear springs on the back and have no wrap problems from the Tdi. I am building up a pair of coiler axles to fit to the parabolics, but I don't see them causing much trouble with the disc brakes - if 109 standard brakes are powerful enough to lock the wheels already, then how much more torque can discs put on the axle? The concern is that the front axle will need to sit higher for the diff and track rod to clear the springs, which will produce more torque. However, I already plan to install a third leaf to each front spring to regain the ride height lost from the taller saddles, and that will help a good deal to resist the braking torque.

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So what we want is some really soft springs that are hard at the same time, designed for a 2 1/4 on 6.50s and drums but running 200tdi or v8 through simex a likes?

Well put it this way, I am currently running a 2.25, with 7.50 tires. The range rover axles are operating off a stock series master cylinder, so don't really have any more force than a set of well maintained drums. (Just more consistency in the wet). And I get so much flex the front prop is binding on heavy braking from speeds as low as 20mph.

This isn't the first set of two leaf parras I’ve owned. The current set (from CP) are allot more flexible than the set I had from DLS previous. I had no problems with the DLS set, and to be honest wish I had kept them.

I was thinking more along the lines of addition helper leafs to counter act the excessive twisting motion, but not provide any weight support under normal load conditions.

It seems to be a reoccurring issue with the CP Springs, and I believe others have probably experienced failures as a result.

The coil over idea sounds good, i might have to see what i can pick up.

Ive been measuring up the possiblity of a set of traction bars. Essentially it would be a kind of four link setup, but the lower two links would be the leafs.

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Using the leafs as links in an anti-tramp setup is IMHO not ideal, you are trying to reduce the work the spring is doing, not increase it.

I have wrap issues on acceleration & braking what with 37" tyres, portals, wilwood discs, and a 4.6 V8, the poor old parabolics get a hard life. The big issue for me is not the behaviour of the vehicle, but the risk of breaking a spring in the middle of nowhere. Wrap is a good way to snap a spring.

I am still pondering revising my anti-wrap setup (full write up on this forum of the current incarnation) to use a shackle-mounted bar which is parallel with the spring, possibly even clamped into the leaf pack itself. Leaf springs are surprisinly complex things to model since they do so many jobs in one and are a flexible suspension link.

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Thanks for the feedback guys, keep it coming.

Ive seen fridges is thread and for reasons explained later, you will see (hopefully) why i'm adopting a differnt approach.

At the moment i'm jsut trying to address the brakign issues and haven't really considered the accleration side of things.

Using the leafs in a 4 link, okay isn't the perfect solution as it may not help much with acceleration flex. But seems to work fine for alot of american trucks with stupid lifts, big tires and silly sized diesel engines.

The reason i'm not going the radius arm route, is that there isn't alot of room to put it due to the rear track rod (and my engine/ gearbox sits lower than fridges) as well as a anti roll bar in the not to distant future. I can't get a setup i'm happy with where there isn't excessive binding which is amplified by trying the fight the rear mounted shackle. The biggest factor of all is i don't really have the facilities to make anything as "durable" as fridges which would handle the binding issues. I've spent alot of time measuring/ calcing the ideal solution and there doesn't seem to be one (for atleast my situation).

A standard landrover one is to long for the use on the front of the series, as the end of it would sit just behind the bell housing crossmember.

After studying the traction rod idea like Sorren fitted it appears it should almost be bind free... if postioned correctly. My plan is only to maintain the diff angle\ castor angle under braking

To behonest i don't understand whats wrong with the 4 link setup using the springs to solve the tramp caused during braking. Providing they are strong enough,by moutning rigid links to the top of the axle casing, you are preventing the rotation ( as over half of the force will be transmitted by the links and enabling it to function purely in and up and down axis, and the only allowable flex comes as a result of the spring length increaisng as it flattened.

If you cater for this extension in the arc of the top rigid link. You almost have the perfect solution to cure the flex under braking imho.

Theres plenty of videos of "before and afters" of trucks being fitted with traction bars on you tube. and it has fairly dramatic results.

As for accelerating, i will worry about that when the t16's in! :D

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Apparently a radius arm off a coil-sprung vehicle is a good way of controlling it?

What with it being a rigid bar then yes, it's as good as any other lump of metal - the problem is how to mount the thing so it resists wrap but still allows the up/down/fore-aft movement of a leafer axle.

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One could make up a mount parallel and slightly in-board of the nearside chassis rail (enough inboard to clear the u-bolts etc.), then a shackle arrangement with a rose-joint on the end of the radius arm?

I guess you mean inside the chasis rail, kind of engien side? If so theres an exhaust in the way.

Heres the basic idea. If it looks a bit wonky thats because i plan to put the links at a 15 degree angle (one either side of the axle. this means they will clear the bump stops brake pipes etc.

The cad model is just fag packet, just chucked together to show the idea.

The links will probably be a rosejoint turnbuckle setup at first.

Concept.jpg

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Maybe going backwards a few steps would help. A proper set of multi leaf springs with there inherant wrap resisting properties mounted using Gon-2-Far style hinged mounts. Would this be a workable compromise between articulation and axle control without the need for additional and complex link systems?

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Ha ha, what a nice marrage............... its a coileavesprung model :blink:

I also have the same issues with springs doing funny things up steep hills (modified multileaf), i am opting for the single link on the middle of the axle running forwards to the bumper. I will rip out my crayons later and try to get a drawing done.

G

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Well.. Using a front hockey stick would limit the wrap but not cure it. You ever seen a defender wrapping the frontaxle? I have many times, problem being the bushes' ability to compress. I suppose this could be one of the problems on your setup too, fridge? Your car being the ultimate in axlewrapping capablity with a fair amount of horsepower and portals, I would say, when you find something that works on your car, it would def. work on everybody elses.

The simple and not ideal way I did it, worked fine for my setup: 900 tyres, 2,5TD engine and 1450kgs of series 2. And I am confident that it would work sufficiently for Meccano as well. Sure my springs still wrapped a bit, I could see it on them after a year of hard abuse, but they were nowhere nearly as bend as my rear springs were.

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  • 1 month later...

How about a DII rear axle Watts link mounted longitudinally with the aft end about 1" lower than the front to cater for the axle's aft movement on leaf spring compression?

Thats a really good idea. :D You should be able to get the "perfect" solution with enough maths.

You could then have it centrally mounted along th axle, and using a rose joint as not to affect the articulation.

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Thats a really good idea. :D You should be able to get the "perfect" solution with enough maths.

You could then have it centrally mounted along th axle, and using a rose joint as not to affect the articulation.

I think you'd have to side it along the right side chassis rail to keep it clear of the engine, but you should be able to connect it to the front cross member and bell housing cross member. The link would ideally be central, but I don't think the engine will allow it. It's worth mocking up, though, just in case it does fit centrally.

It shouldn't matter having the anti-wrap system offset as the amount of force requires to twist the axle case would be enormous. Apart from a brake line which can be re-routed and maybe the oil filter, I think you should have a pretty clear run along the inboard face of the right chassis rail.

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