Jeep Wrangler YJ Leaf Spring Shackle Replacement

Jeep Wrangler YJ leaf springs and shackles are very simplistic in design. But they come with lots of questions.

• What are the torque specs of leaf spring shackles?

• Do I need longer leaf spring shackles?

• Do I need boomerang shackles?

• What are the benefits of boomerang shackles?

• Will boomerang shackles make my Jeep ride better?

• Pros and Cons of extended leaf spring shackles.

• Pros and Cons of boomerang shackles.

  
  

In this article, these questions and others will be answered. Also, lots of tips and tricks, and links to provide more detail.

If you are here for the leaf spring shackle torque spec info, I'll place all that at the top of this article. Just to let y'all know that my priority is to help YOU, I'd make more money putting the torque specs mixed in the text below so it takes you longer to find it. It's a Google algorithm thing .. the longer you stay on a webpage, the higher it ranks, the more money I make. Welp, by placing torque specs at the top is putting YOUR needs first.

Leaf spring shackle torque specs:

Leaf Spring Shackle torque specs. As a general rule for best ride quality and articulation, it's between 35-45 lb-ft of torque. Have your rig sitting on the ground with the Jeep's full weight on the springs before you torque the leaf spring shackle bolts. Before you run off, at least read the next paragraph pertaining to leaf spring shackle torque.

But this torque spec isn't as cut-and-dry as others. It's kinda a "it depends" and a "what you feel comfortable with" thing. Meaning .. factory Jeep torque specs for the leaf spring shackles are around 90-100 lb-ft. Some people feel that torquing the bolts to say 40ish pounds is too loose because the factory specs are so tight. Torquing to factory specs will make it ride rougher because it can bind the bushings, preventing them from doing their job flexing as needed. When I torque shackles to 35 to 45ish I use what's called a Nylock nut (see Amazon link for example). The nylon ring inside the nut is a type of locking feature that prevents the nut/bolt from loosening. Oh, by the way, the Nylock nuts in that Amazon link above will work with your factory bolts if you are re-using them.

Factory YJ leaf spring u-bolt torque specs: Stock-sized Jeep YJ u-bolts torque to 85-90 lb-ft. Larger aftermarket u-bolts will torque higher so refer to the manufacturer's specs for those.

Centering pin bolt torque: Short answer, about 30 lb-ft. Long answer ... the main job of the centering pin is to pull the spring pack together snugly. The second job is to make sure the axle is properly located on the springs. So, as long as the bolt has the spring pack pulled together and are good and snug .. you good. But, I still follow the 30 lb-ft I mentioned above. Generally, there are 2 sizes of leaf centering pins for Jeep YJ's, it depends on whether you have stock or upgraded springs. Sometimes people upgrade the factory YJ bolt to 3/8 so check what size you have before you order. Here are 5/16-18 bolts, and here are the 3/8-16 leaf spring center bolts. You need 2 per axle, so 4 total.

So, let get on with the rest of the article that goes along with the YouTube video.

What are leaf spring shackles?

• Well .. start out with a fun fact. Leaf springs were invented in 1804 (patented in 1805) by a British inventor by the name of Obadiah Elliot. Even though there were simpler forms of suspension at that time, this design became the primary standard in the auto industry and is still used today.

• Just a piece of metal that connects the leaf springs to the frame … yep .. it pretty much that simple. Wellll … Sorta.

Why do we need shackles in the first place?

• Simple .. it allows the leaf spring to lengthen and shorten. 

• As the leaf spring flexes, its length changes from eye to eye.

• Since one end is mounted solidly to the frame, the other end must be movable. That's the shackle's job to allow the other end to lengthen and shorten.

Shackle length .. does it matter? If so … how?

• Stock length YJ shackles are 4” center to center. Some people elect to use longer shackles to get more lift. These longer shackles move the spring farther away from the frame, which in turn rotates the axle down at the shackle end. This does several things, none of which is a positive change. Well .. one of them is a positive change, but the cons outweigh the pros. Let's take a look:

  
  

• It decreases the caster angle of the front axle, affecting the steering stability at higher speeds, and reduces the ability of the steering wheel to naturally return to center after a turn. (see YouTube video for explanation)

  
  

• It increases the pinion angle. If you already have a large lift, it could add just enough angle to vibrations or worse .. start snapping u-joints. (see YouTube video)

  
  

• It increases leverage at the shackle mount. If you have a rusty frame that is starting to weaken, the longer shackles will increase the chances of frame damage.

  
  

• It increases “drop” or “droop,” aka down travel. When talking about axle articulation, there are 2 primary axle direction changes that are talked about the most .. thats going up and down .. I know … duh!! When an axle is going up, it's being “stuffed” or in “compression”, when an axle is going down, it’s in “droop”, “drop”, or “rebound”. Now .. get to the point of the discussion .. the additional “drop” sounds like a good thing … right? Well, it depends; some people's rigs are on the ragged edge of self-destruction due to being improperly built. So the additional drop adds more u-joint flex angle, slip joint extension, and drag link angles.

  
  

• Longer shackles decrease approach and departure angles. Longer shackles stick down farther from the frame, so they will hit more stuff before your tires reach the obstacle.

  
  

• Ok … the good .. the reason most people wanna use longer shackles. You get more lift .. BUUUTTT .. its not as much as people think. For every 1” over stock, you only get ½” of lift. (see end of this YouTube video for proof) Honestly, it's not worth the other issues that it creates. In some cases, where someone wants to install military wrapped springs, 1" over stock length may be needed for clearance of the wrapped spring eye.

Shackle length and wheel travel … yes, it affects it.

• Let's dive into articulation a bit more … or .. “droop” and “stuffed” as mentioned above. Shackle length has a direct effect on wheel travel in BOTH directions.

  
  

• Stuff, up travel, or compression .. take your pick what you want to call it. This is when your axle is as high as it can go on its UP travel. If you have lift springs, your springs are dimensionally longer eye-to-eye than stock springs. Why? Simple .. you wanted a lift .. the arched lift springs are designed to go in place of stock flat springs. The arch gives you the lift .. soooo … to get that lift AND bolt to the factory stock locations, the spring HAS to be physically longer eye-to-eye. OK .. so?? Well, this only matters if you hardcore wheel your rig. If you are pushing your lift springs hard enough to flatten them out, you may run out of shackle swing/travel. If that happens, your springs will sorta deform into a W shape.

  
  

• Reality check - if your rig is primarily a street rig, you have nothing to worry about. If you hardcore wheel your rig, it might or might not be an issue. That really depends on the stiffness of the spring. Most lift springs are stiff as heck anyway, so it isn’t likely that you are gonna flatten your springs enough that you will run out of shackle travel. There is a way to check before you start giving your rig the beat down … more on that later.

  
  

• Droop, drop, rebound … again, whatever you want to call it is the travel in which the axle is at its lowest point in the path of articulation. When in full drop, the axle will stop once the shackles' travel has reached its limit. In this case, the shackle angle will be pretty much in line with the eye of the leaves of the spring. That can be a MAJOR problem!! What's the problem, you ask??? It's called Shackle Inversion, and it can destroy leaf springs.

  
  

• Now, before you keyboard warriors start bashing me about suspension travel limits .. YES I know you can set bumpstops, limit straps, and even shock absorber travel can act as a way to limit suspension travel. Just to be clear .. NEVER allow your shock absorbers to be what limits suspension travel.

How to test for needed shackle length using lift springs.

• All you really need is a string or a piece of flexible wire. Nothing fancy, it just has to be longer than your leaf springs. Tie one end of the string to the frame-mounted end of the leaf spring. Run the rest of the string along the length of the leaf springs until you get to the bolt hole of the other end of the spring. Now you have the total length of your lift springs. Imagine or move your shackle to be positioned at about 45 degrees back. Take that measured length of string still tied to the mounted end and see where it stops on the shackle. If it stops short or on the leaf spring bolt hole … you are good. If the string goes past the leaf spring hole, you MIGHT need longer shackles to get full suspension compression.

  
  

  I say MIGHT … because it's possible your lift springs are so stiff they will never flatten out enough to need a longer shackle. Or, if you are lifting just to look cool, crawling over shopping mall speed bumps .. stay with stock length shackles. So .. lets say you need a longer shackle to allow the spring enough travel to flatten out. Go with the least amount of additional length possible. Remember the lesson earlier about longer shackles messing up steering geometry and pinion angle .. yeah… that still applies. I'll create a YouTube video as soon as I can, showing how to measure if you need longer shackles.

Remember that weird term “Shackle Inversion”. Let’s talk spring damage!

• Shackle inversion can possibly happen when your leaf spring shackle has reached its MAX “droop” level. As mentioned earlier, the spring shackle is inline with the spring when in max droop. What is supposed to happen is that the shackle goes back to its original arch path as the axle comes back up or is going into “compression” travel. Well .. what sometimes happens is the shackle continues the “droop” swing arch and bottoms out on the frame, therefore bending the leaf spring. This typically bends the spring beyond repair .. time to fork out some cash!!

  
  

  Also, it can be a pain to get back into its natural arch while on the trail, so you can limp back to the trailer or home. Jack up the jeep by the bumper or frame (not axle) to take the load off the inverted spring. Using a long breaker bar, pry bar, or even a pipe, pry the shackle back towards its original location. PLEASE be careful .. there is a LOT of stored energy in that spring, so it can be (and probably will be) a violent snap when the shackle snaps back in the correct direction. Sooo .. what can prevent shackle inversion, you ask? Good question, that’s our next topic.

What are those shackles that are shaped like a dog's leg? That would be boomerang shackles!

• Booms were originally intended to give additional travel for the longer lift springs mentioned earlier. They allowed the bent leg to go past the frame due to the dimensionally longer lift springs.

  
  

• They evolved into limiting “droop” to prevent shackle inversion by using the center bolt to hit the frame, therefore stopping the downward travel. Stopping the downward travel just before the bolt holes' centerline is in line with the leaf spring helps prevent the shackle from snapping upward, bending a leaf spring.

  
  

• Proper mounting is as noted: Front - Short leg up - arrow pointed in. Rear - Long leg up - arrow pointed in. Remember, the boomerang shackles "arrow" points towards the inside of the Jeep. Click here for a boom shackle video.

  
  

• I’m not going into a lot of detail on booms in this video. I’ll save the details, facts, and myths for a different video.

Another weird-shaped shackle to mention, tow shackles.

• These are typically triangle-shaped with bolt holes and a hole for a pin.

  
  

• Some people used to mount these backward to allow the center pin to contact the frame, therefore helping prevent shackle inversion.

  
  

• Speaking of shackle inversion, when tow-shackles are mounted the correct way and connected to the tow bar, they have been known to push the shackle up into the frame during a sudden or harder-than-normal stop.

  
  

• Also, since tow-shackles are constantly getting pulled and pushed, they stress the upper mount where it attaches to the frame. Sometimes, it eventually causes the frame mount to break off.

  
  

• Don’t use these for any reason. If you flat-tow your rig, find a way to attach directly to the front frame horns or to a high-quality bumper.

Why do some shackles have a welded center brace?

• You will typically find this only on 2”+ extended leafspring shackles. The intention was to improve handling by preventing the sides from shifting as the leaf springs twist. This is either a good or a bad thing. If your rig is mainly a pavement princess, it can help improve road handling. If yours is a trail rig, it will limit axle articulation. See the video that this article was written for.

  
  

• But remember all the negative things I said earlier about longer shackles, yep … that still applies. ALL longer shackles mess up pinion angles and steering geometry.

Summary

• Only use extended shackles when needed. Such as to clear mil-wrapped springs, or to add a little additional travel due to longer lift springs. Even then .. only long enough to address the issue … NO MORE!

  
  

• Do not use tow shackles for any reason. They will eventually damage your springs or even your frame.

  
  

• Just the installation of boomerang shackles does not improve the ride quality. But, that's the topic of the next video.

Yeah, I know. There ain't no pictures. I'll add some when I get a chance. Fifty-hour weeks at work, fixing a family member's home HVAC system, got stuff to do on the family farm, and trying to get Rust Bucket built ... I have so little time left at the moment.

Peace out! Later y'all !!