Thread: combined trailing arm mount/body outrigger

Hi Jason,

thats not such a simple question ....something a forum could be dedicated to.

Looking at it from a suspension geometry perspective (rather than a engineering exercise), the TA in our Landrovers of this type, that is parrallel trailing arms and A frame, determine the Axle roll axis and paired with the A frame determine the amount of Anti-squat.

Axle roll axis is described as either oversteer, understeer or nuteral. If the TA are sloping down towards the axle it will be oversteer, if sloping up to the axle it is understeer and if level it is nuteral....A stock LR Defender is about +4-6 degrees of oversteer in the rear and close to nuteral in the front.

When you raise a vehicle on its springs you change alot of dynamics. Depending on the vehicle the amount you can get away with varries. The suspension that the Defender 90, 110 and 130 run was originally designed for the RRC. Designed around its wheelbase, its COG, its wheel size etc...When adapting them to the first coil sprung LR there was some comprimise using the same links and geometry, but it certainly acceptable.

Rasie a defender and you are getting further away from the original package.

For me I want to lengthen the TA so I can mount a battery either side where the current TA mount is. It will also lend itself to better handling and offroad driving, even projecting the TA in the same plane it is in now, which on paper will not change the Axle roll axis or the anti-squat, but it does change the arc the TA scribes and therefore the actual Roll steer. It also tends to drive the chassis forward more on steep climbs rather than drive the axle down and forward.

There is alot more to it than this, pages could be written and discussed very easily, but that will get away from the OT.

things have to be considered when doing this, as with anything, one change can/will affect other things....

I was just changing a flat rear tyre on my leaf sprung Stage One and had a squiz at the combined body mount/ forward spring hanger,visualising the different forces it needs to withstand, and began to wonder if we really need to get all that scientific here, as interesting as the discussion has been.

The leaf spring hanger/outrigger is a very simple single 2mm thick skin rectangular member that under all the mud on mine, appears to have full perimeter welds at the side rail attachment. there is a bit of overlap at the top, and a couple of light gussets at the bottom of the main rail and that's about it.I'll check a cleaner chassis down in the graveyard later for evidence of internal reinforcement, but from vague memory I don't think there was.

Just like a standard trailing arm mount,the leaf spring hanger has to transmit for/aft thrust, as well as some antisquat force. Unlike a standard TA mount, it has to cope with some vertical down loads imposed by the body and any payload, in addition to vertical up loads imposed by the vehicles weight. It also has to cope with lateral loading, a job that is performed by the A frame on a coil sprung vehicle. Due to the semi open ended construction, these outriggers tended to fill up with corrosive mud, horse/ cow poo etc,which was almost impossible to completely clean out, which tended to rot the outer wall of the main chassis rail. Yet for all that,to my knowledge these combination bodymount/spring hangers rarely if ever gave any problems, including the chassis rail in that zone.

Bill.

PS, My Stage One is/was a station wagon.The forward end of the rear body does use the spring hanger outrigger as a body mount. Utes and trays don't. On utes/hardtops,it appears that most of the body/payload weight sits on platforms above the main side rails anyway. A properly designed tray should bear on all these platforms too but some designs don't, leading to possible chassis breakage.

good info there Bill. Id rather be prepared with info when dealing with the powers that be so I can half sound like I have some idea and not going to kill innocent families on the road

I stoped by a couple metal cutting folding places today....both said could not do as they use press brakes (ram and V block like John said) I had my terminology confused....I was visualizing a pan brake...Mal Story has a big old one that would be 2m wide Im sure I have seen him fold 3mm in it with ease. Ill have to try a few more places. The other option that one gave me was to cut slots along one of the fold lines. They would laser cut the whole piece and then fold the TA side vertical, then I could "hand fold" the other vertical side....

btw Bill, I did some chasing up on the paint for you. I have another mob to call tomorrow...PM me your phone number

Originally Posted by uninformed

btw Bill, I did some chasing up on the paint for you. I have another mob to call tomorrow...PM me your phone number

Thanks Serg. A brief OT, but if I singe the outer skin of the stump with my oxy acetyline torch, would the primer/paint adhere to it?
Bill.

I'm thinking not...

Originally Posted by Bush65

I don't understand the need for the dimple die holes. Any weight saving may be less than than the weight of sand, mud and water that they will allow.

Good to see someone else shares my thoughts on dimple die holes. They always seem to be added purely for cosmetic effect and always in orientations that will trap a layer of mud/dirt/sand inside. Like lips being pressed upwards in a belly plate.

I work hard to avoid water/dirt traps in everything I design. These people are adding them in for looks alone.

Originally Posted by uninformed

I'm thinking not...

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.

Originally Posted by Dougal

Good to see someone else shares my thoughts on dimple die holes. They always seem to be added purely for cosmetic effect and always in orientations that will trap a layer of mud/dirt/sand inside. Like lips being pressed upwards in a belly plate.

I work hard to avoid water/dirt traps in everything I design. These people are adding them in for looks alone.

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.