What lift to get for my mj

[shelbyluvv]

Blocks will lower an MJ, just saying...

[DirtyComanche]

Blocks will lower an MJ, just saying...

 

That too.

[DirtyComanche]

Now, if you really wanted to be different, I think you could use 56" Chevy springs (73-87 2wd trucks) and install them SOA.  They don't have much static arch, but are obviously a little stiffer.

 

 

Also, SOA with 2wd MJ springs should only be a 3.5-4.5"~ lift on a 4wd truck.

[shelbyluvv]

SOA is a minimum of 5" of lift.

[DirtyComanche]

SOA is a minimum of 5" of lift.

 

Not if you're using springs that are effectively lowering springs.

[shelbyluvv]

Then those springs need to be replaced because they

 

1) can't hold up to any load or towing

 

2) will cause horrible axle wrap

[DirtyComanche]

Then those springs need to be replaced because they

 

1) can't hold up to any load or towing

 

2) will cause horrible axle wrap

 

Neither of those things are particularly related to the static arch of a spring pack.

[shelbyluvv]

Ok man, good luck with that. I'm done with this.

[Incommando]

 

 

SOA is a minimum of 5" of lift.

Not if you're using springs that are effectively lowering springs.

Been there done that: 2wd springs SOA on a 4wd got me 5.25". And those are worn 230,000 mile springs

[DirtyComanche]

Ok man, good luck with that. I'm done with this.

 

Leaf spring rate is mostly a function of the number of leafs, their thickness and width, and the length of the pack.  More leafs, more spring rate.  Thicker, more rate.  Wider, more rate.  Longer, less rate.

 

Static arch does increase the rate by a small factor, although it is an exponential relationship.  That is, within the realm of flat to a moderate amount of arch, say what the factory 4wd springs are, there is a very minimal increase from it.  As arch is increased beyond there, the relationship starts to become more apparent.  This is part of the reason why many aftermarket mondo lift springs ride poorly.

 

Wrap/anti-wrap characteristics are a little harder to pinpoint, as they have to do with the relationship between the three mounting locations, the vehicles CG, the spring rate and configuration of the leaf pack, and about 8 billion other little things.  In general springs with MORE static arch display WORSE wrap/anti-wrap characteristics, but that's a statement that really can only be applied once the arch becomes quite significant.  The other part of the reason those aftermarket mondo lift springs ride poorly is they added spring rate to try to fight the wrap issues.

 

Flat to mild arch (positive or negative) springs typically perform best for everything.  But there's some give and take with that statement.  If you want to go fast, have a lot of power to deal with, and are rule limited in regards to wrap control, and have no huge issues with ground clearance, often a spring under setup with more arch will perform better than a spring over setup with minimal arch.  From a standpoint of what we're probably doing, and if you're looking to add that much (3"+) more arch to the spring pack, it isn't likely the case.

 

I only have a set of factory 2wd MJ springs to measure.  The spring pack is only 1.5"~ thick.  Add that to your axle tube (2.75") and a bit for the perch (.75"), and you're at about 5".  The 2wd springs are at least an inch lower than the 4wd ones (static arch), so that means only 4"~ of lift going from a SUA 4wd spring to a SOA 2wd spring.  Obviously there is variables in play here, some axles have larger/smaller tubes, many spring perches are taller, some people add an overload, not all of the factory springs are the same, or even close, vehicle weights vary, some people can't hold a tape measure, etc.

 

The GM springs I mentioned are from 2wd trucks and are fairly flat, but I don't have a set to compare.  However, they're available with many different amounts of static arch and in different rates, and you can tune them with other flat springs (F-Junk, Wagoneer, whatever).  They aren't perfectly the right length (they're missing an inch behind the center pin, which is significant), so one might have a headache using them, but I'm confident they could be made to work and made to perform well.

 

But thanks for wishing me luck, because I intend to be playing with this setup this fall.