Semi-Related Suspension Question

[YonderNorthwest]

My buddy found some 2" lift JKS springs and fox shocks off of a JLU for a good price. Finally got around to installing them on his JL 2-door about a week ago. His previous suspension was RC shocks and 2" spacer pucks. He has netted about 4" of lift with the new springs (yes, I confirmed that he did in-fact remove the spacers.)

He is reporting that the ride is far worse than how it was on the RC shocks he removed. I have ridden in in his jeep with the RC shocks and the ride was very rough. Planted, but jittery and jarring on and offroad. Now he says the suspension bounces a few times after he goes over events in the road, which is what I would imagine driving without shocks would be like.

My theories:
- Weight difference between 2-door and 4-door is what is causing the excessive lift. Now the 2" shocks are extended 2" too far at 4" of lift and he doesn't have enough down travel.
- Geometry issue caused by the amount of lift with no other supplementary mods (adjustable control arms, trackbar relocation, etc.)
- Weight difference is doing wonky shit with the dual-rate springs he installed.

Here are some photos he snapped for me at lunch today. 2nd to last picture (with the anti-rock) is for reference. Notice the difference in the coil spacing between his front coils and mine.

Appreciate any suggestions y'all have for him to fix the issue he is having.

 

[Chris]

How is the shock travel bias after installing the new springs?

 

[YonderNorthwest]

How is the shock travel bias after installing the new springs?

Check out the photo of the rear shock. I don't know anything about the JL, but that looks like a lot of shaft showing for a stock mounting location compared to what I usually see on TJs. That leads me to believe his bias is off. You can also see a difference in the wear on the exposed shaft near the top compared to the rest. I wonder if that is the difference in bias between where he is at now and where it was on the donor vehicle.

Edit: Google AI says a stock JL should have between 7" & 9" of shock travel.

 

[Chris]

Check out the photo of the rear shock. I don't know anything about the JL, but that looks like a lot of shaft showing for a stock mounting location compared to what I usually see on TJs. That leads me to believe his bias is off. You can also see a difference in the wear on the exposed shaft near the top compared to the rest. I wonder if that is the difference in bias between where he is at now and where it was on the donor vehicle.

Missed that one!

That's his problem right there. Even without measuring that shock I can tell beyond a shadow of a doubt he's got tons of up-travel and very little down travel. That's gonna translate to shocks that bottom out during every day driving.

I could be wrong but I highly doubt there should be that much shock shaft exposed at ride height.

 

[JMT]

If your buddy is getting the amount of lift he wants out of the JL springs, then he needs to measure for proper shocks. That is always the bottom line. I'm fairly confident that he needs new shocks of proper length.

 

[YonderNorthwest]

If your buddy is getting the amount of lift he wants out of the JL springs, then he needs to measure for proper shocks. That is always the bottom line. I'm fairly confident that he needs new shocks of proper length.

33" tires he's got on there now are only about a year old. The goal was to retain the same 2" lift but without RC shocks and a spacer lift.

 

[GATORB8]

JL springs are almost universally sold with lift marketed compared to a heavy Rubicon. His 4" net is around where I'd expect it.

I echo the others that you may be near one end of the shock travel.

 

[GATORB8]

33" tires he's got on there now are only about a year old. The goal was to retain the same 2" lift but without RC shocks and a spacer lift.

I'd guess you only need one inch of bump spacers up front with the right shocks. Although I have aftermarket fenders, I'm running that bump setup with 38s on the JL.

 

[GATORB8]

View attachment 685472

Maybe disregard my bump comment, pretty sure that's not your buddies JL in that picture with 3" of bump.

 

[GATORB8]

Here's the standard Fox 2.0 sizes on that setup with 2" of bump. Droop side travel isn't as bad as I expected unless they are the short size. The top section has shock ride height lengths if you want to back check, I plugged Rubicon +3" from your reported 4" lift.

 

[YonderNorthwest]

Sounds like the least expensive option for him would be to swap back to the springs and spacers. Thanks for the help!

 

[Mike_H]

Springs set height, shocks control ride. If he liked the ride height on the other set of springs and spacers, throw those in and then measure the shocks extended and compressed length, then the length at ride height so you know where you are in the travel. Everyone knows the ride gets harsh when you bottom a shock out on compression. Not nearly as many know that you get the same effect when you run out of travel on extension. Gravity and inertia will continue to pull the vehicle down when the shock hits its downtravel limit. It can momentarily loose contact with the ground, then when it hits, you feel it as a buck almost, since you're travelling in a downward direction, and all of a sudden, the tire crashes back to earth and needs to rapidly change direction (compress).

 

[GATORB8]

Sounds like the least expensive option for him would be to swap back to the springs and spacers. Thanks for the help!

As another option if money is the big issue, he could find a set of 4 door rubicon take off springs for next to nothing.

The mopar lift front LCAs are actually really inexpensive and would gain him a little caster. I think new from an online dealer, they are like $75 for the pair.