SOA Ideas and Speculation/Rambling

[BeenJaminJames]

So I've been thinking... I can't stand the SUA design of these rear ends.  All weight is supported by the U bolts in tension, hanging off the threads.  That's definitely something I'd like to eliminate.  Plus you've got that big bracket hanging down under the axle, so if a tire slips offroad and the ends of the U bolts stab down into the top of a stump, you're not going anywhere without a jack.  So I definitely want to convert to SOA.  But I don't want to lift the rear of my truck more than about 2-3" as it will and does see alot of highway/towing use with a smaller set of street tires.  Then I had an idea.  Our springs are 60" long with quite alot of arch in them.  Fullsize chevy springs are 63" with very little arch.  There's enough room to relocate the front eye of the spring forward 1.5" easily enough, and something could be done with the shackles to take up the extra length in the rear.  What I haven't been able to find, is data.  I've searched, but can't seem to track down the amount of arch in the MJ springs compared to fullsize chevy springs.  I know it's been discussed here before, as I remember seeing a thread a long time ago where it was mentioned.  I also have no idea how the spring rates would compare.  I'd like to find a good balance between articulation and cargo capacity.  It is my understanding that the chevy springs are less progressive than MJ springs due to having fewer leaves.  What are your thoughts, ideas, and suggestions? 

 

Mods, feel free to move this thread if it doesn't belong here

[Eagle]

So I've been thinking... I can't stand the SUA design of these rear ends.  All weight is supported by the U bolts in tension, hanging off the threads.

You are over-thinking, and worrying about things that don't need to be worried about.

 

The u-bolts are 14mm diameter. Even at the weakest grade for carbon steel, the tensile strength is 58,000 psi. Each u-bolt will support 13,837 pounds in tension -- and there are four u-bolts per vehicle. That's 55,348 pounds.

 

The load on the rear springs of a fully-loaded metric ton Comanche is how much? 2,800 pounds? 3,000 pounds at most. That's a safety factor of 18.45:1. The greatest safety factor I can recall hearing about in structural engineering class was 6:1. How many MJs have you ever seen with the axle fallen out because the u-bolts broke?

[HOrnbrod]

Free arch is 9.5".

 

[BeenJaminJames]

You are over-thinking, and worrying about things that don't need to be worried about.

 

The u-bolts are 14mm diameter. Even at the weakest grade for carbon steel, the tensile strength is 58,000 psi. Each u-bolt will support 13,837 pounds in tension -- and there are four u-bolts per vehicle. That's 55,348 pounds.

 

The load on the rear springs of a fully-loaded metric ton Comanche is how much? 2,800 pounds? 3,000 pounds at most. That's a safety factor of 18.45:1. The greatest safety factor I can recall hearing about in structural engineering class was 6:1. How many MJs have you ever seen with the axle fallen out because the u-bolts broke?

 

 

I'm aware they're more than strong enough... but I still rather have soa purely because it makes me feel better.  Will I ever break the u bolts? Never.  But it won't hurt.  And there's still the ground clearance issue of having the bracketry hanging down. 

 

Awesome blueprint, thanks!  9.5" is alot of arch.  And I always thought the mj springs were 60" instead of 57.  Good to know.  Also I'm somewhat surprised that the axle isn't centered in the middle of the spring.  So this might not work so well, will have to get hold of a set of chevy springs to measure.

[Pete M]

just plan on retaining your MJ mains.  that'll keep everything where it should be. :thumbsup:

 

XJ leafs are pretty flat.  you might get close to your goal with a set of them (cut the eyes off and put the entire pack under your mains).  just be sure to properly support your mains. 

[yxmj]

just plan on retaining your MJ mains.  that'll keep everything where it should be. :thumbsup:

 

XJ leafs are pretty flat.  you might get close to your goal with a set of them (cut the eyes off and put the entire pack under your mains).  just be sure to properly support your mains. 

 

:thumbsup:

 

If I could add,,,, take a couple of minutes and clean and inspect the leafs.....older ones have hairline cracks that the rust hides.....if you are going to do it make sure it lasts  :thumbsup: .

[neohic]

Here's an interesting thread on using Grand Wagoneer leafs in a SOA configuration while not going ridiculously high.

 

[Pete M]

your link links to the photo

[neohic]

your link links to the photo

 

:doh: Let's try that again...

[Automan2164]

http://comancheclub.com/topic/23624-grand-wagoneer-rear-spring-soa-swap-done-more-pics-added/

[BeenJaminJames]

Those wagoneer springs would be perfect... if only it were within the realm of possibility for me to find a decent set.  I doubt anyone sells new replacement leaves, but I'll look around.  The truck in that picture is the perfect height, actually maybe a bit higher than I'd like, but not so high I'd complain.  Unless I can find a good source for 5 leaf SJ springs, the search continues....

[Automan2164]

Try BJ's offroad. They specialize in FSJ'S and you could probably pick up a new set there. I know they sell lift springs, stands to reason they would have normal ones also.

 

Rob

[Automan2164]

Yup.

 

http://www.bjsoffroad.com/ProdList.asp?scat=126

 

Rob

[Pete M]

the truck in that pic is lifted more than 2-3".  what exactly is the plan for this truck?  seems to me that to a certain extent the amount of lift I wanted would trump the precise method of lifting.  bigger lifts cost more. bigger lifts mean bigger tires.  bigger tires mean crappy acceleration, leading to needing better gears.  it's a never ending cycle of spending.  :(  seems like a lot just in case you might someday get hung up on the ubolts.  :dunno:

 

look into the U-bolt eliminator designs.  between those and some relocated shock mounts, you can create a reasonably smooth underside.  :thumbsup: 

[Incommando]

FSJ springs aren't hard to find new and you can get them from several sources. Rancho's 44044 FSJ springs are a very commonly used spring in SAS for IFS fronts and SOA on Wranglers, etc... if you start to look there may be more used versions out there anyway. Heck I scrapped four used FSJ springs last fall because I could not give them away.

 

One thing I would do for a short SOA is use the smallest, cheapest spring perch I can find. Those Mopar one's look pretty short. You could cut your own out of rectangular tubing and possibly go lower. I went with Barnes4x4 stuff on my SOA for the extreme beef and larger u-bolts/spring plates but they do sit higher off of the axle. For reference with well-worn 2wd leafs I got 5" of lift with my SOA. 

[Eagle]

I wheeled my '88 MJ for several years with a 4" lift and 31s and I never touched the u-bolts on any obstacle. If that's a major concern, it should be easy to fab a couple of u-bolt skid plates.

[BeenJaminJames]

the truck in that pic is lifted more than 2-3".  what exactly is the plan for this truck?  seems to me that to a certain extent the amount of lift I wanted would trump the precise method of lifting.  bigger lifts cost more. bigger lifts mean bigger tires.  bigger tires mean crappy acceleration, leading to needing better gears.  it's a never ending cycle of spending.  :(  seems like a lot just in case you might someday get hung up on the ubolts.  :dunno:

 

look into the U-bolt eliminator designs.  between those and some relocated shock mounts, you can create a reasonably smooth underside.  :thumbsup:

 

Yes on second look, that truck is definitely higher than I want to go.  At first glance I thought they were 31" tires, looked at the wheel gap and thought, "well that's a tad high, but close enough."  I'm trying to maximize ground clearance as much as possible, while still keeping it low enough to not look more than slightly awkward on 29" highway tires.  I'll be primarily hauling and towing with the truck, and will use either the 235/75/15's I have now, or more likely a 30" tire since I don't think these 15's will fit over the brakes I have in mind.  That's a highway-only tread.  For offroading, I keep a seperate set of larger m/t's that never get aired up or run on the street, and unlock the swaybars while I'm under there.  I currently run 31's as nothing larger is practical at stock height.  If possible/practical, I'd like to shoot for a height that can allow me to run a 30" highway tire, and a skinny 34" tire offroad, even if some inner fender clearancing needs to be done.  That's a 2" (actually more like 2.5") difference in the radius of the tire, so it seems feasable to have a 34x9 that barely clears without making the 30" highway tires look too out of place. And yes, while I agree that there's nothing particularly WRONG with spring under axle, I just don't like it, and I'm stubborn.  And I hate it.  I live on the side of a mountain (or hill, if you've been to places where they have real mountains) and often use my truck to go down below the bluff to harvest firewood.  I can't count how many times I've had a full load, gotten hung up on that bracket, and had to unload the bed so my puny jack could lift the axle off of whatever stump the u-bolts have dug into.  Keeping to the high spots isn't always possible.  The lowest point on my 240sx sportscar is about the same height as those brackets, 'nuff said. ;)

 

FSJ springs aren't hard to find new and you can get them from several sources. Rancho's 44044 FSJ springs are a very commonly used spring in SAS for IFS fronts and SOA on Wranglers, etc... if you start to look there may be more used versions out there anyway. Heck I scrapped four used FSJ springs last fall because I could not give them away.

 

One thing I would do for a short SOA is use the smallest, cheapest spring perch I can find. Those Mopar one's look pretty short. You could cut your own out of rectangular tubing and possibly go lower. I went with Barnes4x4 stuff on my SOA for the extreme beef and larger u-bolts/spring plates but they do sit higher off of the axle. For reference with well-worn 2wd leafs I got 5" of lift with my SOA. 

 

I've never even seen a grand wagoneer in person.  Only heard about them in fairy tales and online forums.  Lmao they're pretty rare around here.  I did see a J10 once, it was too cool.  Perhaps they just weren't that common here, or perhaps their massive weight combined with local scrapmetal prices has contributed to them all dissappearing.  I'll be building my own perches, so the springs will sit 3/16" above the top surface of the D44 axle tube.