Shackle Length and Info Sorry it's long Questions in first few lines

[skidoo_j]

So I've come to regret installing the XJ shackles on my MJ.   That being said I'm trying to find factory ish replacements and am locating alot of mixed information.   I no longer have my factory shackles.   With that said... 

 

What is the Stock MJ shackles  length center to center?????    I've searched this high and low both on ComancheClub, naxja, and general google.   Lengths I've found so far: MJ (4.125, 4.5, 4.75, 5, 5.15),     People claim using Comanche shackles on an xj nets 0.75" lift so theory would hold that MJ shackles would be 1.5" longer   so   4.625 (4 5/8")?   

 

 

Lengths of other shackles I've found consistent but still may not be true

XJ are 3.125,  

Tomken Machine  4.125"

Ironrock    IR-XABBS  

JKS   5.125"     Confused because in some places they advertise 1" for both xj/mj with the same product and that's not possible.

Rubicon Xpress boomerang 6".  

 

 

edit   comanche  4 3/8"  by 4 member measurements

 

I've also found that some people are using chevy shackles....  I've found lots of them that match our width, but again varying information on "stock length".   I"ve found 4"  several times for a stock chevy silverado,    so does that mean the 1" drop shackle measures 6" eye to eye or is it' not the same 50% rule because they're inverted?    I like the fact that the chevy shackles are half the price of "jeep" shackles.     

 

 

Basic shackle info...  

 

Boomerang style shackles only provide increased clearance and could possibly reduce probability of spring inversion as the bend serves as a limit.  

 

45 degrees is not the "best"  angle...        On a stock spring xj or near flat spring this maybe true as the shackle will move towards the front of the vehicle in both compression and relaxation.        On curved springs a 90* angle in relation to the springs mounting holes is "neutral"  if less than 90 it will increase spring rate, if greater it reduces.  

 

Best information I've found on determining how long your shackle should be:  Get a string tie to front mount bolt, run it along the arch of main spring to get, main spring length eye to eye, then pull taut.   have second string attached to shackle mount bolt, find length of string off shackle bolt to intersect taut string off spring mount.  this is your perfect shackle length.     anything longer will allow springs to bend over,  anything shorter and the springs will bind.     I've done this test now three times and get 5" roughly each time.  So I"m thinking factory shackle was 5"  but I want to confirm. 

 

 

Hind sight is always 20/20.   I"ve researched this alot and have filtered out alot of the well my uncle bil says  bs.     

 

Sources:

http://comancheclub.com/topic/15988-rear-shackle-interchange-question/?p=161869

Here you can visually see the JKS is longer eye to eye than a set of "factory" mj shackles

 

Old vs new:





 

 

 

 

yet another side by side by another comanche member showing the jks eye to eye about 1" longer than stock:  

 

Well I got these JKS shackles in the mail, and went out to compare them to the originals, and these new ones are an inch longer and look like they will lift the truck in the rear.  The description says that the shackles shouldn't provide any lift on a Comanche, but you can tell by the picture that they are not the same as the originals.  Back to the drawing board I guess, will probably just use the originals.

 

 

 

[skidoo_j]

I had other sources linked, but I must have exceeded the lines allowed.

 

http://www.quadratec.com/jeep_knowledgebase/article-93.htm

http://www.jeepforum.com/forum/f12/tech-topic-boomerang-shackles-1379950/

 

http://comancheclub.com/topic/812-shackle-length/

[Pete M]

it'll still be 50% because the other side of the leaf springs is fixed. 

 

the ones on my MJ trailer measure 4 3/8" eye to eye.

[skidoo_j]

it'll still be 50% because the other side of the leaf springs is fixed. 

 

the ones on my MJ trailer measure 4 3/8" eye to eye.

 

THank you for the measurement.   

 

One question...   eye to eye the same as center to center?   Maybe this is why there are so many discrepancies...  I view them as two different measurements, but Maybe I"m incorrect.     Here's a drawing as to how I understand the two measurements please correct me if I'm wrong.

 

 

[Pete M]

eye to eye = center to center

 

:thumbsup:

 

my head was thinking they were 5 1/4".  I'll go check one of the trucks and see if they jive.

[Pete M]

my 88 has the same measurement. :thumbsup:

[Jeep Driver]

You PM'd me, I'll answer you here-

 

 

You get no lift from the JKS shackle. Eventhough it is 1" longer, because of it's shape and the way it's installed, the overall height remains the same. The extra length will run parallel to the spring, not perpendicular.

[skidoo_j]

You PM'd me, I'll answer you here-

 

 

You get no lift from the JKS shackle. Eventhough it is 1" longer, because of it's shape and the way it's installed, the overall height remains the same. The extra length will run parallel to the spring, not perpendicular.

If there is a difference in the distance between the holes then there is a difference in ride height. The shape of the shackle makes no difference in any behavior other than clearance or possibly providing a stop to prevent inversion.

 

 

 

 

 

Anybody have a set of shackles from an MT MJ to see if they're the same ?

[Jeep Driver]

I have them on my truck and there is no difference in ride height.

 

You asked, I answered.

 

 

And BS on the distance of the holes and the shape as it relates to height.

If the shackle hanged STRAIGHT up and down, one inch in length translates to one inch in hight, however, the boomerang shape allows the eye of the spring to move further back on the truck......that was the point I was trying to make that you missed.

The one inch is canceled out by the new position of the eye of the spring.

[HOrnbrod]

Here's what JKS says about their own "Boomerang style" XJ shackle if this is the shackle you all are referring to:
 

HD Shackle Features

• Boomerang style shackle optimizes rear suspension travel by allowing full compression and extension of leaf springs
• Extended length increases rear ride height 1 in. for improved tire clearance
• Greasable Dura-Thane chassis bushing is included for smooth, quiet operation and easy lubrication
• Rigid design prevents binding and bushing fatigue commonly associated with OE and inferior shackle designs
• Heavy duty construction ensures correct operation of springs and bushings under severe off-road conditions
• Durable powdercoat finish provides long-lasting protection

[Jeep Driver]

 

 

This way.......maybe.

 

But according to others this is backwards.

 

Also, when installed this way you cannot get a grease gun to the zerk.

[mvusse]

XJs with lift springs need shackle relocation brackets or boomerang shackles because a stock straight shackle will hit the back of the bracket when the springs are compressed. The stock springs are nearly straight at ride height, so both up travel and down travel cause the shackle to swing forward but there is very little room for the shackle to swing back as happens when lift springs compress.

 

As to the OP, my stock MJ shackles measure 4.375" long center to center verified by tape measure. I believe XJ ones are 2.75", but that's from memory. The closest one at hand is 4 miles from here somewhere in a pile of parts in my shop.

[HOrnbrod]

 

 

This way.......maybe.

 

But according to others this is backwards.

 

Also, when installed this way you cannot get a grease gun to the zerk.

 

From the JKS shackle installation instructions on an XJ:

 

3.   INSTALL XJ SHACKLES

Position XJ Shackles in the original location with the JKS decal facing forward (front of vehicle) to ensure correct operation and maxi-mum suspension travel.

 

Mount XJ Shackle to leaf spring and chassis with original hardware, but DO NOT tighten mounting bolts.

 

But for an MJ I'd reverse them with the decal facing the rear.  For the Zerk fitting you could always drill and tap a 1/4x20 hole on the other side for another Zerk fitting.

 

[skidoo_j]

The direction a "boomerang" shackle is installed will not change the effective lift. The only way a shackle with a greater distance between the holes would not cause an increase in lift would be if the main spring changed length, if badly fatigued, or broken. Different springs could also negate the lift from a longer shackle.

 

JKS boomerang will net 1/4" lift. Its minimal but still a lift none the less.

 

 

Yes, the truth of the matter is you can have any shape shackle you'd like and it doesn't make a bit of difference between mounting point to mounting point. It can be straight, boomerang, S shaped, or shaped like a lighting bolt. The only thing that matters is the angle from mounting hole to mounting hole. The rest is all about packaging and preventing "shackle inversion" which was stated originally (we'll get into that in a minute). Here's some pics to illustrate what I'm talking about. The last image is them all overlaid.

 

 

 

 

 

The angle of the shackle however, can soften or stiffen the spring's normal rate. You can find the angle of a shackle by drawing a line through the middle of both spring mounting eyes, and a line through the shackle pivots. Then find the angle made by the two lines. You can increase the effective rate of a leaf spring by decreasing the shackle angle. An increase in shackle angle will produce a decrease in the effective leaf spring rate of a leaf spring.

 

Here's 4 more images of the same spring in a compressed state. The last one is them all overlaid.

 

 

 

 

 

This brings us to "shackle inversion". Shackle inversion is when the leaf spring droops past it's maximum point. This happens when the axle is fully drooped out and something hits the shackle (or leaf, or axle attached to the shackle) forcing it to compress in the opposite direction. It usually leads to a bent or broken leaf spring, and most people choose a "boomerang" style shackle to avoid this.

 

 

*all pics were made by 87jeepwrangler over on the jeepsunlimited forum*

Now on to shackle shapes, and how they affect things.

 

Up until a few years ago, shackles were simple, strait pieces of metal, then came the tow shackle, and the boomerang shackle. The tow shackle is pretty simple, still 2 pieces of metal, but provisions have been made to allow the hookup of a tow bar for flat towing. Sometimes they are run backwards so that the tow bar attachment point is towards the axle of the vehicle, and with the pin installed will act as a shackle stop to reduce the chance of shackle inversion. The boomerang shackle was origionally designed for the rear of YJ’s. In the rear of YJ’s with lift springs, as the suspension compresses, the longer length of the main leaf and the added travel the shackle has to account for it would cause the shackle to contact the rear cross member limiting travel. Back in the day, before boomerang shackles, we’d just notch the crossmember where the shackle hit and things would be good. The boomerang shackle was just a bit more BLING way of getting around the problem. Boomerang shackles are also used by some in a front application with the short leg towards the frame to counter shackle inversion. Some mistakenly think that the different shape of the boomerang shackle will alter the angle of the shackle or how it travels through its range of movement. This is not true, the shackles angle is measured in a strait line between its mounting points, it can be a boomerang, zig zag, strait, or round, the shape does not change the angle of the shackle. On an unrelated note, this is why bent drag links and trac bars don’t change bump steer, the mounting points dictate the angle, not the shape of the bar.

[skidoo_j]

Found stock length replacements. Iron Roock budget boost.   http://www.ironrockoffroad.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=IROR&Product_Code=IR-XABBS&Category_Code=PFX