Thread: combined trailing arm mount/body outrigger

I recall Ralph Posch and Sam Overton both did this mod (On a S1 hybrid with a disco chassis and a RRC and ) respectively. Both were happy with the result, however I have no pics of the mounts. I can't recall any failures. Sam's RRC is probably long gone - and has been through multiple iterations. Ralph's S1 is still in daily use on Flinders Island.

Originally Posted by wagoo

OK thanks Serg.

Back on topic. Good luck with DOT, but I'll throw another idea out there if they knock you back.
You may be aware of the after market long arm kit for YJ Jeeps, that retain the standard chassis mount location for the TA, and bolted a 'J' shaped TA to a bracket at the rear of the axle tubes instead of the front?
The result of what I'm suggesting may or may not end up looking a bit homely, but I was visualising using a front axle radius arm in place of the rear axle TA , but only utilising the one bushing on the axle end, sleeved down to accept the standard TA axle bush. A very rough measurement under my hybrid whilst dressed in my best clothes revealed that this may work if the pin end of the RA could be machined back 50mm on a lathe, or 25mm and the chassis bush re fitted to the front side of the chassis mount and spaced forward 25mm.This would give an effective increase of around 150 mm in TA length without changing chassis mount or axle location. The axle bracket could almost be made a bolt on/clamp on affair if your DOT don't like welding to axle tubes.
Of course I don't know how this would work out geometrically with regard to antisquat, under/oversteer etc. I can't find my compass and protractor to draw it out
Bill.

Very interesting Bill, I was not aware of this style for Jeeps. I quickly threw my tape measure on mine and I think the RA would have to reduced by more than 50mm to work in length....The front and rear axle tubes are pretty close for OD so that side of things would be ok. As, you I cant quite guess the result of geometry without drawing it and I also wounder if there would be any change to the axle end loading from changing the bush from front to rear? As the rear end flexs more than the front, the cup in the RA that goes around the axle tube may be to close and bind during cross axle articulation.

At this stage I think it wouldnt really be worth the hastle and would not give me the room to do the battery trays etc where the TA mount already is.

Originally Posted by wagoo

( IT ALSO TENDS TO DRIVE THE CHASSIS FORWARD MORE ON STEEP CLIMBS RATHER THAN DRIVE THE AXLE DOWN AND FORWARD)

You are basically describing anti squat forces there Serg, which I assume is another thing you desire to reduce? I wonder if the A S geometry of the standard arrangement is all that high.The way I visualise it, Anti squat is performed by the axles torque reaction lifting the rear of the chassis via the pins on the chassis end of the trailing arms. Yet on RangeRover Classics at least, those pins (5/8'' dia) are almost as soft as licorice sticks. If the A S forces of the original set up was significant, those pins would bend on just about every RangeRover, except possibly the one driven by Grandma. Yet bent pins aren't that common except on vehicles with raised suspension, where on suspension droop the chassis end bushes of the TA exceed their limit of compliance.

Bill.

Yep, and Im still trying to figure out how, if you extend them along the same plane as OEM, that it changes. I was told this by Sam Overton, that he found better hill climbing with his extended arms, I figured they had lowered them.... As Ben noted, Sam had extended his and some others forward to the body outrigger, in the same plane as stock......I also asked how he did the mounts and he said he just cut the OEM mounts off and moved them forward. I had touble visulaizing the actual end result without it being absolutely booty fab... I never saw any pics and new that I was missing something as Sam is pretty switched on.

Ben, maybe Chucks truck is done also???

FWIW, the main chassis rails are still sweeping donw between the TA and the body outrigger. If I make my mount the exact same as the OEM one, the arm will mount 20mm lower at the body mount location. This with the added length will change my TA angle from 13.65 degrees to 8.79 degrees...

And, the AS will change simply by wheelbase and tyre size, so even with the same spring height, My 110 wheelbase and 32 inch tyres will have more AS than the 100 Rangerover on 29's....of coarse this based on the same COG height, which wouldnt be true...but you know where im coming from.

food for thought.

But lets stay on the mount before we get all geometric Im struggling with the simple stuff here and I think John may feel like he is dealing with a special needs kid.

See bold responses:

Originally Posted by Bush65

My opinion hasn't swayed from when I said:

I got the impression that the main reason you thought I was modding the body outrigger was the top plate width, looking at my original pics it was hard to tell that the top, at chassis, is the same width as TA mount. You now know this and have elaborated.


The dynamic load from the trailing arm can and does vary from very high compression (in some circumstances equivalent to the vehicle weight), to fairly high tension. The magnitude of the load fluctuation is the difference between the two extremes, i.e. it is much greater than either the peak compressive or tensile load. It also undergoes an enormous number of load cycles and both of these factors lead to fatigue failure, unless the maximum fluctuation in the stress is below the endurance limit.

I have pointed out the issues of welds where fatigue is involved and attempted to explain how the load was transferred from the TA to the top and bottom flanges of the chassis within the stock TA mount.

Avoiding fatigue is not about adding material, gussets, etc. all over the place like “belts, braces and nappy pins”. It is all about attention to the details that matter, such as minimising the effect of stress raisers, minimising residual stresses, and eliminating defects/flaws where cracks can start. For example the fatigue strength of axles/half shafts can be increased by waisting to the root diameter of the splines.

Loads will always (without exception) take the stiffest route in their general direction. This is where material is used efficiently, where stiffeners play a great role even if they might look insignificant and where stress raisers should be avoided when fatigue is an issue (stress raisers are not an issue with static loads).

In your modified body outrigger design you have added a gusset between the vertical legs to transfer the TA load. The great majority of the TA load must be transferred through this gusset and the plate that you intend to weld underneath. Have a good look (based on pics that I posted before) at how the path of these loads through the gusset and bottom plate. Now compare this with the stock TA mount design.

How many welds can you count across the path of the load in each of these designs?

none on the OEM mount, edit, 1 on the OEM mount if you count the weld were the inner 4mm plate is welded along the lower fold to the 3mm main body:

4 on mine:

#1, the bottom plate to vertical face
#2, the bottom plate to bottom of internal gusset
#3, the gusset to vertical face
#4, the guesset to top plate through slot for welding

One thing I was thinking of doing is using one peice for the gusset and the added internal plate on inside face of vertical leg. This would be 4mm and a simple 90 degree fold. This would reduce 1 of the welds...

The welds connecting the stock mount to the chassis are unavoidable, but their location, direction, length are fit for the purpose.

Welds, even those executed perfectly, reduce fatigue strength. The direction of the weld has a large effect, as I indicated in an earlier post. Defects in welds are not acceptable where fatigue is a concern. Fillet welds are worse than butt welds.

Because you don't have good access to weld both sides of your gusset and bottom plate, you will not be able to make a good weld and prevent defects - backing strips would help, but IMHO the design is flawed and this is what should change.

Internal gusset can be welded both sides. I can fit my MIG gun in there with good angle and this would be welded on bench before fitting to chassis as the gusset is not weled to the chassis rail. The top and bottom of gusset would be welded via a slot cut in top and bottom plate, this would result in a edge to egde weld.

Bottom plate would be fitted last, in postion on chassis. I have looked closely at the bottom plate at RA and front body mount, both of these are only welded on the outside, not internally.

Have you considered access for welding the mounts to the chassis and the difficulty of welding in positions other than downhand?

Yes, as a carpenter I am use to dealing with pysical limitations over those of a simple pen stroke in a design. I have thought all along about the fabrication process and fitting of mount and one of the reasons I have made a full size mock up. I know that vertical down is not considered ideal in structural welding, but have been lead to believe it totally acceptable in welding materials 3mm thick.

The body load on the outrigger is smaller than the TA and always in the same direction, so the load fluctuation is much less than that from the TA.

IMHO it is better to give priority to accommodating the major loads, i.e. TA load in this case. Quite often the design for the major loads will be untroubled by the minor loads or only small changes or tweaks are required. This is why I made the statement at the top of this post. You have done the reverse and exposed your design to considerable difficulties, including fatigue failure, access for welding, and access to the bolts for the TA bush.

My preference would be similar to what Slunnie suggested, using Patrol TA bushes.

I went back and re read Slunnies post, though I was a bit confused when he mentioned not overlaping top and bottom of chassis rail, but then said weld it to the sides, making sure it contacts the top and bottom, plates....now without overlapping, this would mean the corners, which we have already discussed as not being a good idea.




However if I were to stick with the LR TA to chassis bush I have used an old cardboard carton to show how I would base it on the design of the LR mount – see pics below.

Bend the 3 mm thick plate as shown in the pics by the cardboard mock-up against the LR TA mount.
Now take your modified outrigger mock-up which is wider (horizontal direction) where it joins to the chassis rail. The rearward vertical leg stays as is and welds (use virtual welds for cardboard) to the new TA mount. The chassis bush for the TA bolts to this as per your earlier pics. It should also have the same doubler plate.
The forward vertical leg of the outrigger needs to be shaped to fit against the new TA mount – see dashed line in second pic. The TA mount can be trimmed back to leave a stiffener as shown by the solid line in the second pic.
Finally add the proposed bottom plate from end of outrigger to underside of TA mount.

IMHO a better design for the outrigger is to press up 2 'L's instead of a 'C' plus bottom plate. Joining the 'L's together to form the box section involves no more welding but they are simpler to press than a deep 'C' section.



All of you questions pretty much relate to understanding the same issues. Think of it this way: load is carried by the stiffest part.

For example take two coil springs of identical length, but one is soft and the other is stiff. Say the load to compress each spring 1 mm was 1 Newton for the soft spring and 100 Newton for the stiff spring. Now if the springs were arranged one inside the other so that a load compressed both springs simultaneously, by an identical deflection. If the load was 101 Newton you should clearly see that both springs will compress 1 mm and the soft spring will only carry 1 Newton while the stiff spring carries 100 Newton.

If we want to increase the load capacity of a structural member, one way is to add material where the stress is most severe, but we can only achieve the desired result if the material is added where it is sufficiently stiff.

Take roof sheeting. The thin sheet can carry considerable load (compared to flat sheet) because the material is stiffened by the ribs.

Material too distant from a stiffener is not capable of carrying as much load as it can close to a stiffener. The thicker the material the further the distance it can be from the stiffener. Stiffeners can take many forms, such as ribs, webs, flanges, corners in LR chassis rails, pressed lips, virtually anything that constrains the element from flexing (flex is the opposite to stiffness – recall what I said about loads and stiffness) to in thin direction and forces it to remain straight while subjected to the design load.

I'm sure you would have observed when building a roof, that when the trusses are first stood up they can't carry large loads but as purlins are added, the load capacity increases because the purlins keep the top chord of the truss straight. In this case the purlins “stiffen” the chord in the direction in which it was previously able to flex.



Thick steel sections and plates are rolled by a “hot mill” - the steel is red hot while it is rolled.

Sheet and strip is first rolled on the hot mill and further rolling, to produce thinner sheet, or to form it into sections such as hollows (shs, rhs, chs), 'C' or 'Z', etc. is performed in a cold mill (sheet and strip) or in a roll former (a series of rolls where each set of rolls produces an incremental change in the section shape from the flat strip to the finished section).

I will re read, and re read. Please dont think I am disagreeing with you in any way. It would be all to easy just to say ok and how would you do it....in which case I could have just said "John, please design this for me"

Im sure you are seeing large differences between my mount and the OEM type with regards to the TA and its forces. Im just not seeing that great a difference and am trying to understand.

BTW, I spoke to another sheet metal mob and they said it would be no problems folding up the main body "c"....his words were as long as the web was greater than 100mm then they generally can fold the toes, legs etc longer than it is.

With my current design, and it may be hard to see, but the front vertical leg is not as tall as the rear where TA mounts, this along with the width change, creates a compound angle and would be a bit more difficult to fold in 2 seperate L shapes...

again more food for thought for me.

feeling pretty dumb right about now

Originally Posted by uninformed

I was adding them for a few reasons.

#1 to stiffen the large thin top surface.
#2 to reduce some weight.
#3 more access for hosing/cleaning out as the gussests form compartments.

My bottom plate will have any dimples or flanges down not up.

I am happy to not dimple the top if they will not be functional.

For access and weight reduction any holes will work. But I'm not overly convinced of the stiffening properties of round flared holes. Creases or cross-breaks work well to stiffen sheetmetal and provide support over a whole length. Any hole pattern results in lines of no reinforcement.

Crease in a hotrod floor:

1968 Pontiac Firebird - Floors & Firewalls

Cross break in sheetmetal:


But back on topic. I second John's comments about designing it as a new trailing arm mount and incorporating a body mount second.

Originally Posted by Dougal

For access and weight reduction any holes will work. But I'm not overly convinced of the stiffening properties of round flared holes. Creases or cross-breaks work well to stiffen sheetmetal and provide support over a whole length. Any hole pattern results in lines of no reinforcement.

Crease in a hotrod floor:

1968 Pontiac Firebird - Floors & Firewalls

Cross break in sheetmetal:


But back on topic. I second John's comments about designing it as a new trailing arm mount and incorporating a body mount second.

You may sitting on the fence regarding dimples, but others clearly are not

Structural beams used to stop large concrete wall panels breaking when being lifted off the ground in a horizontal postion, to there final vertical resting place:





Tread plate on the scaffold stairs I walk up and down about 38 billion times a day...



Yep Im familiar with the concepts in the pictures you have shown, and as you used the term "Sheet metal" I have really only seen them in 2mm thick and less....mostly less.

It gets to the point of being the absolutely best design would probably mean a whole new chassis . Alot of good designs require a more complex shape than can be simply folded....then its the turn of many 100's of tonnes press and dies to "stamp" or "form" the part....the LR OEM TA mount is such a part...not just simply folded.

So with out expensive production line machinary Im back to a more simple design and maybe some compromise with welding.

BTW, I thought you said I was on the right track....whos side are you on anyway????





















Im guessing the side of better, proper design

The precast slab supports, the holes are there for weight reduction and to provide very convenient fixing and lifting points. The rolled edges (not just dimpled) mean they won't cut into lifting slings.

The tread-plank of that design I personally don't like. They flex a lot because there is no continuous path of metal across to carry the load. I have used similar designs (but without the open raised perforations) for slider beds in fruit dewatering conveyors. But I put cut and folds through them to add stiffness across and stop them sagging.
But for a lightweight portable tread or plank they do the job.

I don't think you'll need a new chassis just for this (but feel free). Plating the rail for reinforcement and a plate wrapped mount with a body mount bracket will do the job.
Exactly the geometry and size that will work the best is always the hard part. That eats the most time in all design jobs.

Originally Posted by Dougal

The precast slab supports, the holes are there for weight reduction and to provide very convenient fixing and lifting points. The rolled edges (not just dimpled) mean they won't cut into lifting slings........

weight reduction yes, lifting and fixing, no. There are no fixings through these large holes (say 100mm dia) and while there may be the odd time a lifting sling is thrown through the hole of one or 2 of these NOT attached to any pannel, they are NEVER used as a lifting point.

As you said earlier, any hole will provide weight reduction...and the 4mm or so material these are made from wouldn't really trouble a true lifting sling as far as abrasion.

I do how ever agree with you (and John) regarding my design.

Am I correct in saying the major difference (and flaw) between my design and the OEM TA mount would be the welding?

breaking it down:
The vertical face is the same design and thickness, so this is ok.

The diagonal free face/edge that goes up and overlaps the top rail is one peice, stiffer and has no weld at the top where mine would, to the top plate in my design.

The diagonal bottom plate that goes from the vertical face to the inside bottom corner of rail, is folded from the main face, thus no weld?

what else am I missing?

Since my vertical face is the same, and also includes the same 4mm internal double plate, it seems to me the main problem is my gusset, which is acting as the diagonal free face....but lacks the ridigity and has welds at vertical and top plate rather than one single peice.

Im thinking the bottom diagonal plate is not quiet as a problem as LR have no stiffener or fold etc on it....I would have thought my bottom plate, attached to the inside corner in the same manner as LR, be up to the same task.