Pumpkin spice..

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J Mack said:
This exactly what I'm dealing with here.
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With full weight they are still back from vertical.
I would want them at vertical or slightly forward of vertical with no weight.

You hire some of the best guys around to work on these pigs for you and it will be interesting to see what you guys come up with.
On a side note did they look at caster numbers on this one yet?
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Man that just looks wrong. Not that I'm an expert. Looks like it will be even worse (as Jim said) when you drop the motor in.
 
WarDamnEagle said:
Man that just looks wrong.
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My opinion is the same, there is something called “shackle jacking” or something like that and it describes the way the shackle loads the spring when it’s trying to compress, it’s not desirable and Dobinson setup appears to embrace it.

I had a similar but opposite issue with the OME lift spring and shackle, somewhere buried in the middle of my 10 year ago or so build thread I posted links to useful information (most likely dead by now) handy calculators and how I addressed them. There is plenty of sites with great information centered around off-road racing and the categories that require leaf springs, it’s not unusual to see a 12” plus long shackle on a spring under setup. The solution to our issue is a longer shackle for me the number was around 7”. I’ve said mutable times for a spring under I would shoot for something vertical plus a few degrees at full droop and something less than 45° at full compression.

I looked for some useful information but I’m out of time and need to get some work done today. This video is good at showing some of what we are dealing with here.









Here’s what I would ask of all my internet friends here. If this is an interesting subject and we would like to continue to talk about it someone start a ”PIG suspension geometry” thread so we don’t have 52 pages of side track in the middle of this thread where we solve the worlds troubles only to be lost and brought up again in three months.
 
gonzopancho said:
TBC: the body was _not_ set all the way there.
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it was NOT set on the frame in that photo

Those springs have a couple hundred pounds of frame on them, that’s it, nothing else.


Once we have some real weight I’ll report back for those curious about the dobinson suspension
 
J Mack said:
With full weight they are still back from vertical.
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that's not anything like full weight. the (sprung) weight there is basically "the frame". no engine, no transmission, no battery, no bumpers, body, interior, fuel, ....
J Mack said:
I would want them at vertical or slightly forward of vertical with no weight.
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that does tend to be the preferred setup, with weight on and 'static'. With no weight? I don't know how you're going to achieve that. When unloaded the spring is going to maintain the factory arch. The eye to eye length vs. the location of the hangars is going to determine the static shackle angle, but now we're into the weeds and you wanted to start a welding on factory frames "pig suspension" thread, so I'll wait for that.
J Mack said:
You hire some of the best guys around to work on these pigs for you and it will be interesting to see what you guys come up with.
On a side note did they look at caster numbers on this one yet?
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no man. I said I'd do it today, but it's not even 9am yet.
 
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why can't you simply install 4-degree caster shims?
for what it's worth (and I have zero expereince with FJ55's but I am a Dobinson's distributor) I find their shackle angles to be way too aggresive on all their offerings, 40, 60 and 70 series. I actually don't really push their leaf spring products at all as a result

As for Dobinsons leaf springs "killing" caster, I would say that is absolutely true, every rig I have seen with them have a -1 or -2 degree caster angle before any corrections
 
cruisermatt said:
As for Dobinsons leaf springs "killing" caster, I would say that is absolutely true, every rig I have seen with them have a -1 or -2 degree caster angle before any corrections
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I would 100% agree that if and when these springs "settle" we would be in the minus caster territory.
 
cruisermatt said:
As for Dobinsons leaf springs "killing" caster, I would say that is absolutely true, every rig I have seen with them have a -1 or -2 degree caster angle before any corrections
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factory spec is +1° any increase in shackle length is going to rotate the trunnions to take that away.

and it's easy to see why: big heavy truck (for it's time), no PS, bias-ply tires. they didn't want to add a lot of steering effort.
 
gonzopancho said:
factory spec is +1° any increase in shackle length is going to rotate the trunnions to take that away.

and it's easy to see why: big heavy truck (for it's time), no PS, bias-ply tires. they didn't want to add a lot of steering effort.
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Yes I am aware of what the factory spec is and why, I always aim for around 3-4-degrees especially with mods like PS
 
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