XJ shackle with custom springs question.

[Trav3lingman]

Got a reasonably solid but high mile XJ for a DD/Project/Part time mild off roader. 355k as of now. Super saggy rear springs when I bought it. Replaced with Omix-ada. Was a mistake. They started sagging almost instantly.

Had a local leaf spring shop make me a custom set. Wasn't looking for lift at the time. Just a fair bit of extra load rating and no sag. (Specifically I told them I wanted about 600 lbs of extra load ability and as they are a very experienced shop they said no problem.)

They made them with and extra leaf and much more of the leaves run nearly the full length of the top leaf vs the factory stuff.

The springs sat my house for a few months. A few days ago I did a complete front end rebuild. Literally replaced everything but the axle and steering box.

Bought some new ZJ V8 coils. And installed them along with the custom springs. After a week of driving etc I'm sitting at 1.5 inches over stock in the rear, and 2 inches over stock in the front.

Goal is to run 265/75/15s as I scored a near perfect set of 5 teardrop wheels for $170 bucks.

My thought is .75 spacers up front and 1.5 lift shackles inch rear. Which would be be almost dead level and fairly even wheel openings.

But my question is.....with springs that are heavier load rated but not specifically arched to provide lift like normal lift springs are....will the ride be much harsher with 1.5 inch lift shackles and will I need boomerang style keep the angles correct?

 

[XJlimitedx99]

with springs that are heavier load rated but not specifically arched to provide lift like normal lift springs are....will the ride be much harsher with 1.5 inch lift shackles?

That depends on the current shackle angle. If your shackle is currently vertical, longer shackles will have almost no effect on the effective spring rate. The farther forward your shackle is leaning (as it sits now), the greater the change will be with the longer shackles.

If, for example, your shackle is currently at 45° to the spring datum line while sitting at ride height, putting longer shackles in will move that angle closer to vertical and increase your effective spring rate.

Regardless, it won't be a drastic change. I actually like to advocate for a steeper shackle angle for anything other than a dedicated offroad rig. A vertical shackle is best for vehicle dynamics. If the ride is too harsh with a vertical shackle, the spring rate is too high.

will I need boomerang style keep the angles correct?

Boomerang style shackles have no effect on suspension geometry/dynamics. What is important is the imaginary line between the two shackle bolts. The shackle could be shaped like a... well, you know, and it would still function just the same. Boomerang shackles are used only to prevent interference with the springs or with the rear crossmember.

 

[Trav3lingman]

Ok so I need to check my shackle angles now that it's probably settled fully. (About 400 miles of mixed interstate and city driving on the parts now.)

I like to wheel on occasion but I also like a fully functional DD and carry a lot of crap with me due to traveling for work. So heavy springs were needed for sag prevention. It rides and drives quite well now other than the worn out steering box and I'd like to keep it that way but most people looking at shackle lifts were using re-arched lift springs or diy packs so I wasn't sure how it related to my setup.

 

[Trav3lingman]

That depends on the current shackle angle. If your shackle is currently vertical, longer shackles will have almost no effect on the effective spring rate. The farther forward your shackle is leaning (as it sits now), the greater the change will be with the longer shackles.

If, for example, your shackle is currently at 45° to the spring datum line while sitting at ride height, putting longer shackles in will move that angle closer to vertical and increase your effective spring rate.

Regardless, it won't be a drastic change. I actually like to advocate for a steeper shackle angle for anything other than a dedicated offroad rig. A vertical shackle is best for vehicle dynamics. If the ride is too harsh with a vertical shackle, the spring rate is too high.



Boomerang style shackles have no effect on suspension geometry/dynamics. What is important is the imaginary line between the two shackle bolts. The shackle could be shaped like a... well, you know, and it would still function just the same. Boomerang shackles are used only to prevent interference with the springs or with the rear crossmember.

Ok so I finally got a chance to actually look at my shackles. They are actually tilted backwards some. Which I'm assuming is bad. https://photos.app.goo.gl/es8fravXaoUV5KgM9

Guessing I'm going to need SRBs no matter what. Springs are new and so are the shackles. Maybe I wasn't paying attention and put them on backwards?

 

[RCP Phx]

Shackle angle is good, but you might need some boomerangs so they don't hit the frame bolts.

 

[Trav3lingman]

Shackle angle is good, but you might need some boomerangs so they don't hit the frame bolts.

 

[Trav3lingman]

I'm still trying to wrap my brain around shackle geometry. It seems like the shackle being tilted backwards would be a bad thing. But as these are heavy leaf springs compared to stock springs or most lift springs in general I'm still trying to figure out how it all plays together in my specific setup.

 

[RCP Phx]

You really won't know anything until you install the springs. The more the shackle angle the softer the springs will appear.

 

[Trav3lingman]

You really won't know anything until you install the springs. The more the shackle angle the softer the springs will appear.

The picture link I posted is actually with the new springs installed.

 

[RCP Phx]

Bought some new ZJ V8 coils. And installed them along with the custom springs. After a week of driving etc I'm sitting at 1.5 inches over stock in the rear, and 2 inches over stock in the front.

Goal is to run 265/75/15s as I scored a near perfect set of 5 teardrop wheels for $170 bucks.

My thought is .75 spacers up front and 1.5 lift shackles inch rear. Which would be be almost dead level and fairly even wheel openings.

To run those tires it sounds like you need some 2" front spacers and some 1-1/2" shackles.

 

[RCP Phx]

It was late, the actual math says 1" spacers for the front!!!

 

[XJlimitedx99]

Shackle angle looks good. The shackle's job is to allow the leaf spring to extend/retract as it flattens/droops. As the shackle swings backward during suspension compression, the leverage of the system changes such that the effective spring rate decreases. From a vehicle dynamics standpoint, a constant spring rate is most predictable to the driver. In the offroading world, many people recommend the shackle be angled with the top towards the front (like yours) to get more droop from their suspension.

You should be fine to install longer shackles.