Extended spring perches?

[d_r_1989]

k so my axles off, took some pictures of the axle and the perches. Not good




I know pictures are crap but its kinked the axle when its tried to wrap the springs and failed with me having add a leafs previously.

This wasnt done by me either so please no question of my quality of work! i think off i hadnt used add a leafs and the ends of the per hes were welded up for extra reinforcement i wouldnt be here right now!

[Anton]

Anton as the springs flex the position of the axle changes, during compression the spring flattens the axle moves backwards slightly, further away from the chassis mount. During droop the spring arches more and the axle moves forwards. This is why a lot of people fit the shackle design to allow for this movement.

Yes, I was thinking of using a top link the same length as the chassis to perch part of the leaf spring, and making sure it sat at the same angle. My thinking is that as the springs flex upwards the top link would follow them in an identical arc. This should stop the link binding up and forcing the axle to rotate, shouldn't it?

I know pictures are crap but its kinked the axle when its tried to wrap the springs and failed with me having add a leafs previously.

Yikes! That's not good at all! I guess adding a bam bar would've spread the rotational torque across 3 points on the axle instead of 2, but that's a good reason not to skimp on your leaf perches if ever I saw one!

I definitely have axle wrap, when I put my foot down in 1st I hear the rear driveline bind up and it makes a gut-wrenching clicky/grindy noise as I murder my UJ's. I'd like to do front and rear bambars, so that I don't suffer from wrap up front under heavy braking either. I really should get longer driveshafts too, and get rid of the spacers so that my driveline is at a more sensible angle.

But I do think that a bambar is the way forward for now.

[d_r_1989]

Well my new perches are on and strengthened a lot more than the above. Abit worried about the axle casing but time will tell. Guess a wrap bar is needed for spoa with a td engine, well once Iv bled the brakes it will be next on my list.

[ScottieJ]

https://web.archive.org/web/20130615134 ... ch/bambar/ Finally found the old jeepaholics Bambar tech article, shame that website has gone as there was a lot of good tech on it, at least it's archived

[d_r_1989]

Would that design be better than nylon admirals do you think?

[Anton]

As far as I can tell, they're the same except for the fact that the admiral of nylon made a shackle to go into his to allow for more movement than the jeepaholic guy allowed for. That is to say, his shouldn't wrap at all, but might bind a bit on articulation and force the nose of the diff to move at an angle the leaf springs don't want them to be in.

The admiral's one won't do that, but will allow for a bit more wrap. I'm thinking of making mine more like the jeepaholic guy, but also in such a way that I can add a tiny shackle if I find it binds up.

[NylonAdmiral]

As Anton says, they're essentially the same. The only difference is the inclusion of the shackle which allows for variance in the length of the tether.

There are a lot of different designs but they all employ the same core functionality.

The main difference comes down to the number of "points" on the axle and whether or not the design includes a variable length tether.

Mine has two points on the axle (i.e. the bottom of the A-frame). Some only have a single point where a rose joint (heim joint if you live in the US) is fitted to to the top or bottom of the axle, the tether then fixes to this. This design is fairly useless and doesn't reduce any wrap, it just constrains the point about which it can occur.

Assuming you are going for two points on the axle, the only decision is whether or not to go for a variable length tether.

When the springs compress, the top of the axle will be constrained by the tether and the bottom of the axle will move backwards a small amount thus forcing the diff into a "nose down" position. It won't be much but it will happen. If you have a lot of lift and your prop angles are tight then you increase the risk of your UJs binding. The severity will depend on the shape and flexibility of your springs.

If you use a shackle and have it set up right then this binding wont happen and your pinion angle won't be negatively effected. However, you will get a tiny amount of axle rotation and therefore a small amount of wrap.

TL;DR

Without shackle = tiny amount of binding.
With shackle = tiny amount of wrap.

You have to weigh up which of those is preferable to you but neither option is going to be anywhere near as problematic as the wrap incurred without an anti-wrap bar in place.

I decided to go with a shackle because I'm running at the limits of my prop angles and I believe the wrap to be significantly reduced but not completely eliminated. I would prefer to have no binding or restraint on articulation at the expense of a marginal adverse effect on spring fatigue.

Neither design is better than the other, you just need to work out what suits you & your vehicle.

[Anton]

I don't think the tiny amount of binding is going to limit articulation on standard springs personally, but I stand to be corrected. The way I see it is:

Bambar with Shackle: Slightly easier on the UJ's
Bambar Without: Slightly easier on the springs
No bambar: vastly less life from springs *and* UJ's.

I think that if you do some maths and work out geometries and such, you can probably build a setup that has no disadvantages at all. I'd like to build a setup where the bambar could double as a top link if I ever 3 link/coil it (with panhard). Which is the biggest if in the history of my truck...!

[NylonAdmiral]

I don't think the tiny amount of binding is going to limit articulation on standard springs personally

I doubt it too.

Bambar with Shackle: Slightly easier on the UJ's
Bambar Without: Slightly easier on the springs
No bambar: vastly less life from springs *and* UJ's.

Pretty much yeah, except that if you don't have a lot of lift then you shouldn't need to worry about the UJs anyway. The problem is of course that we're only talking about antiwrap bars to negate the problems which come from SPOA which is done to create lift. I don't know what the limits of the prop angles are but I expect there's a window in which you can have some lift without having to worry about the UJs binding when the pinion angle is forced downwards in a fixed length design.

I think that if you do some maths and work out geometries and such, you can probably build a setup that has no disadvantages at all.

I'm pretty sure that whatever you do, the trade off will always be the same.

[Anton]

Well, I was thinking that since the axle moves in an "arc" trajectory with the leaf springs (rotating around a central axis, that is to say, rotating around the bushes fixed to the chassis) so if you can work out the geometry, you should be able to make a top link that simulates the natural arc that the axle follows when it articulates. Then you should have no binding.

I could easily be missing something though!