XJ rear sway bar on MJ

[Anthi4078]

Hey I was just thinking and I’m wondering if it would be possible to put a rear sway bar out of a XJ onto a MJ? I know some fabrication would be needed to mount it to the body but other than that everything should line up right? 

[cruiser54]

Check with Addco. 

[acfortier]

Addco makes one that is for the MJ: https://www.sdtrucksprings.com/index.php?main_page=product_info&products_id=23571

Got one in my basement, but it hasn't been installed yet.

[gogmorgo]

There’s a couple write ups in the DIY list, not specifically the XJ sway bar, but other similar junkyard sourced parts. 

 

[CheepComanche]

4 hours ago, acfortier said:

Addco makes one that is for the MJ: https://www.sdtrucksprings.com/index.php?main_page=product_info&products_id=23571

Got one in my basement, but it hasn't been installed yet.

I was looking at the Addco rear sway bar a while back and saw that it said no drilling and "bolt on" on the website. Maybe I'm missing something but I can't see how it would be a direct bolt on. 

[gogmorgo]

My understanding is the Addco uses clamps to hold the sway bar to the axle and then uses an L bracket to bolt the end links to the upper shock mounts. This is why the kit only works on the short bed MJ, long bed trucks have the shocks ahead of the axle so they can’t reuse the mounts. I’m also not convinced it’s the best place to mount the end links. You do occasionally see someone break the shock stud off the frame rail, and that’s without the added stress from the sway bar on it.

This thread’s got a couple references and a diagram of the Addco. 

I’m not sure what to make of Limey’s complaint about the kit. Not enough context. You definitely need some form of roll control up front if you want to run a rear bar, and that description is basically what happens with a rear sway bar only, or if you’re trying to wheel with one on. The sway bar tries to keep the axle parallel with the body, and you don’t necessarily want that if the body is leaning hard because of what’s going on up front. 
 

[Eagle]

If you stiffen up the front sway bar (larger diameter) and do nothing in the rear, you increase understeer (plowing).

 

If you install a rear sway bar and don't run a front sway bar, you get oversteer (probably -- or at least a lot less understeer).

 

What you're looking for, ideally, is a balance between the front and the rear anti-sway control so that under most conditions you don't get either massive oversteer or massive understeer. I believe the auto manufacturers prefer to build in a little understeer, because they think people can handle that better than oversteer -- and they're probably right. Personally, I prefer just a bit of oversteer under throttle, and neutral steer when coasting.

 

[cruiser54]

And you lose rear articulation with a rear bar. 

[gogmorgo]

Well yes. Sway bars keep axles parallel with the vehicle body. Disconnects are definitely a good idea if you want to run both off and on road.

But in terms of cornering, if the body is rolling and you keep the rear axle parallel with it, you're going to lift the inside rear tire (possibly far enough to roll the vehicle), and the outside rear is going to be leaning over onto the sidewall, severely limiting traction. You don't want to run a rear bar if you've got nothing up front. But I do sometimes see people in groups for vehicles that came with two sway bars recommending removing the front and leaving the rear sway bar on the grounds it's generally stiffer and therefore has a bigger articulation benefit than removing the rear, with the mistaken belief it will still allow some roll control on-road. And it's terrible advice.

You can't really use sweeping statements like "sway bars make understeer or oversteer" because it very much depends on how the suspension is set up. What they do is keep the axle parallel to the vehicle body, which in turn helps to control changes in suspension geometry as the vehicle body rolls, which goes a long way towards handling predictability.