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Oh Jesus Tits....
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Discussion Starter #1
Have been tossing around the idea of a 3/4 eliptical setup on my truck. The curb weight of the truck is around 4000 lbs and uses 2.5" leaves in the rear. I have a couple old Nissan Main leaves laying around that I could cut up and use, but I don't think they're robust enough to hold up and would likely snap the first time I flexed it out. The truck is a '98 Nissan Reg Cab Frontier. Still IFS, but the front is locked and lifted, and the steering is beefed. The SAS will come one of these days, but for now, the front ARB keeps pulling the short shafts along, and I happen to have a ton of spare parts for it laying around.

Anyone have thoughts on what springs would work well for this? How about shackles? I have 4.5" shackles now (1.5" longer than stock). When driving on the road, I want the top leaf to rest on the frame and only open up during flex. I've also considered using some kind of clamp that slides along the frame so it doesn't open up during normal driving, and I could also clamp it down on hill climbs and descents to keep the rearend from unloading. (especially downhills)

Any help is appreciated.
 

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I'd ditch the idea of the 3/4 eliptical setup. It seems to me that all it does is let the axle drop without adding any down pressure (like a revolver shackle). FWIW, I think you'd be better of tuning on your standard leaf spring setup as it is simple, proven, and can really flex well if built properly.
 

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Flexy Flatty said:
It seems to me that all it does is let the axle drop without adding any down pressure (like a revolver shackle)
No,

you can do a 3/4, where the top 1/4 elip has compression and does not sit flat againse the frame. In this configuration you could make your upper 1/4elip the equal rate to your lower 1/2 elip leaf and would increase your up and down travel while maintining the same "down pressure" as just the 1/2elip.

axle warp is a problem, and the this setup will have more trouble locating the axle so you may also need a panard bar and tracktion bar...

The longer the upper 1/4elip is the more you will need a panard bar.
The softer you make the top 1/4 elip the more axle warp you will have and need a traction bar.

So if you make the top 1/4 elip really stiff you have less problems with axle warp, will not "need" a traction bar, but will have minimal flex advantages, but may give desired height, almost like jsut a shackle lift.

If your 1/4 elip is short you will have less problems with axle location and will not "need" a panard bar, but will have less added wheel travel.

If your 1/2 elip leaf is 150lb/in thats only 75lbs/in on each eye of the leaf, so for a matched 1/4 elip rate with some up travel youd want about a 75lb/in 1/4 elip... correct?

So how long of a top 1/4 elip can be used with out really needing a panard bar. I was thinking of using about a 25in 1/4 elip off a F350, either only the top leaf or top two leafs (stiff) to minimixe axle warp. The 1/2 elip is about 25in from the shackle to the axle center so the frame end of the top 1/4 elip will mount directly above the axle center! is that too long to have any axle location...

Any non noobs with some trial and error experience have input....
 

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Oh Jesus Tits....
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Discussion Starter #4 (Edited)
Trial and error is exactly it. With varying weights and F/R weight distributions of vehicles, it's probably going to be a case by case basis. I have room on the flat part of th frame above the axle for a pretty long 1/4 eliptical spring, but I'm not thrilled at the idea of not having that spring sitting on the frame for highway travel to and from the trailhead (this thing isn't a trailered rig - it has AC and windows :) )

I like the idea of the F350 leaves, but aren't they like 3" wide? I could use an unequal width shackle I suppose to connect the two. I had planned on attaching the thing to the frame with Ubolts and a locating pin.

Again, I'd be interested in hearing from anyone who has messed with these setups as to wheter this idea is even worth considering because it seems real good on paper.

Thanks guys.
 

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D-RAT said:
Ashman, I've seen you on the Nissan boards, haven't I? BTW, I run www.Nissan4wheelers.com
Yea, MCsoo or "MCfly" i think mikes name on that board. hangs out there, I check up every now and then.

F350s leafs like mine, 70s years, are 2.5in wide same as my lower pack.

They are thick leafs and have many in the pack. I plan to use jsut the main leaf and maby the second if I need to stiffen it up.. not flexy like the nissan main leafs but would be more stable....

Worst case you build arms to fix the 3/4 elip warp and wandering problems then later $$$ converter to coil overs....


some F350 leafs...
 

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Oh Jesus Tits....
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Discussion Starter #7
Good to know on the F250 leaves. Will do a little more digging on the feasibility. Will need longer brake lines and I'm a little concerned about my driveline length (embarrasing to pull out a slip yoke!)
 

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D-RAT said:
Good to know on the F250 leaves. Will do a little more digging on the feasibility. Will need longer brake lines and I'm a little concerned about my driveline length (embarrasing to pull out a slip yoke!)
Well the axle will move twards the transfercase on drop, so will push teh drive shaftinto your slip yoke on drop and wont fall out, it can only bind on drop...
 
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