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OP, how heavy more or less according to your calculations is you rear end ? and how old are those RK 2.5" springs?. Few months ago when i was researching coil springs to lift my rig i found a few threads from people saying the rear RK springs were a little on the soft side and they were not holding back a lot of weight. I'm talking about old posts i've found in 2013, 2015, 2016 etc. I wasn't interested in heavy rate springs so i started doing more digging as i liked the price on the RK springs and decided to buy them based on more recent posts, i went with the RK 1.5" coils myself, RK04186/RK04187 as of a few months ago.
I already had mods when i did the rears, so my Jeep butts is about 300lbs heavier than stock and with the RK 1.5" coils i have my butt is lifted 2" with respect to stock

I used this diagram to measure, basically from the edge of the bumpstop cup to the bumpstop pad
Font Line Parallel Circle Drawing

in my case,my stock numbers for the rear were 5" on both sides. with the RK 1.5" springs and 300lbs of weight in the rear (steel bumper, spare/carrier, toolbags/recovery gear,security enclosure etc, etc), my Jeep is at 7" in the rear on both sides. I don't know how much rear lift the RK 1.5 springs would have given me stock, i know the fronts one were 3" even, so i'd assume 2.5" perhaps
20211026_090122 by RAM RSM, on Flickr

If your rear is really that low it's possible you have old tired springs, maybe the spring rates were not that great before, maybe you have an insane amount of weight back there ?

Try a newer set of 2.5" springs as i'd think they changed the rate from years ago so you can start fresh at 2.5" and adjust with a small spacer, or go straight to 3.5" springs. My RK rear 1.5 springs measured 16 7/8', so according to their chart, the 2.5' are about 3/4" taller, and the 3.5's are 1.5" taller compared to the 1.5's. Again all this numbers are from their springs i bought brand new couple of months ago. They have 4 different flavors on spring height, in theory 1.5" and 2.5" have the same spring rate, i don't know if that changes on their 3.5" and 4.5" versions. Talk to RK to check.

RK04187$199.00 per pair1.5"17.043"5.596"
RK03101$199.00 per pair2.5"17.730"6.680"
RK02002$199.00 per pair3.5"18.590"6.730"
RK06014$199.00 per pair4.5"19.500"7.100"


You can always use spacers to get back to where is needed. I'm doing that with my RK 1.5" fronts. i got 3" stock with those, and after weight i went down to 2.25", (bumpers, winch, skids, sliders etc etc), so i have a 0.75" Daystar in the front now and went back to 3" with mods. The ride is super plush so i'm hanging into this springs for a while :)

I'll also upgrade the rear control arms to something with better bushings, Go with Clayton Overland + arms, Metalcloak, Synergy, Rancho, etc, any of the ones with DDB bushings, they're maintenance free like the stock clevite ones, but a lot stronger and flexy compared to those. I love the Giiros in the Claytons, i have a 7k lbs truck with those in the rear, have them in there for 2 years, set it and forget it, they flex really nice and their bushings are self centering and fully sealed. Also Clayton rear TB with the same Giiro bushings, but if you want to save some dove, Superlift with reflex bushings are a bit cheaper, that's what i have in the back of my Jeep, while i have the Clayton in the front. Having good bushings in the control arms and TB should tight up that but when loaded, asides of course from having good coil springs that can support the wight you have.

Have fun.
 

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I'd think you'll want them nipple up cause then you can route the hoses through the openings at the top of the spring tower to avoid pinching them.
 

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Disconnect the trackbar, disconnect the sway bar links, loosen up lower control arms, disconnect the shocks from the bottom, put 2 Jack's on the frame with wheels off, then droop the axel slowly. You will be able to take the spring out easily, slip the bags in and put everything back. Sway bar links and trackbar are prob the most time consuming items to deal with in the whole install.
Good luck.
 
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