Sagging stock front springs?

I did some more experimentation and measuring, and learned a few things.

First off, dropping the tires to 26psi and increasing the damping on the shocks has improved the ride noticeably. Thanks @bobthetj03 for the tire pressure recommendation! I tried a range of higher and lower pressures, and settled just where you suggested. The damping on the shocks is now at 6 of 9. I figure that's giving the suspension some more support during compression to keep it from hitting the bump stops so hard. Those two changes have also helped dampen some of the smaller high-speed bumps.

I also measured front suspension travel in a variety of driving conditions around town, on the highway, and on reasonably civilized dirt roads. It looks like I'm typically using about 2" of travel.

IMAG0647.jpg
That's using up about 1/2" of bump stop compression, since there's only about a 1.5" gap between bump stop and axle pad.

The furthest I pushed the suspension, which was probably from body roll when I bounced into a driveway, was just below the top end. I'm not sure I want to hit the front end hard enough to see if it will go further, but it looks like I'm not hitting the end of the shocks during normal driving. (Not wheeling, mind you.)

IMAG0637.jpg

I also jacked up the frame until the front wheels were off the ground to see where the front suspension was sitting in relation to full extension. Here's the front suspension at rest (ignore the zip tie) ...
IMAG0632.jpg
... and at full extension, where the zip tie is marking the at-rest position ...
IMAG0652.jpg
... so that's about 2.5" of stroke left for compression, and about 4" of stroke available for extension.

Along the way I learned that the bottle jack is not really adequate for lifting 31s off the ground when you've got so much extension left in your shocks. I stuck a piece of wood under it to give it a boost, but I figure I'll cut some 6x6x2 wood squares and take them with me if I need to use the bottle jack in the future. That would also help stabilize the jack if I have to use it on soft ground.

While I was at it, I made the same measurements with the rear shocks, at rest ...
IMAG0656.jpg
... and at full extension, where the zip tie marks where the shock was at rest ...
IMAG0653.jpg
... so the rear shocks have about 3.5" of stroke left for compression, and about 3" available for extension.

If the shocks are supposed to sit about halfway through their travel, the rear shocks look OK, and the front shocks are sitting a little low.

I don't know if anyone is still following at this point, but my plan is to replace the front springs and see where things end up. If that doesn't do anything, I may add a 10mm spacer to the front to open up the gap between axle pad and bump stop a little.

I have a trivia question, if anyone read this far. I did some searching, and was surprised I couldn't find spring rates for stock or aftermarket springs. Seems like you would want to know your spring rates if you're trying to match springs to a heavier-than-stock rig. I guess the stock springs must be something close to 300lbs/in for both front and rear.

Anyone know what the correct stock spring rates and uncompressed spring lengths are?
 
The factory fronts are approximately 140lbs/in. I don't know what the rears are or the free lengths for either end. I'd like to know for my own curiosity.

Most lift springs are going to be in the 130-250lb range, with the majority being below 200lbs/in. Unless you are somehow mixing and matching front and rear springs from the far reaches of the spectrum, you are highly unlikely to notice any differences in the ride. Shocks are the largest influence of that.
 
Did you compare the measured space between bump stops and the amounts of exposed shock shaft? Looking at it quickly, the numbers don't look like they ought to. Remember that overall stock travel was roughly 8" split 50/50.
 
Yeah. Axle pad to bump stop cap is about 3", maybe a little less. Exposed shock shaft is about 2.5".
IMAG0628.jpg IMAG0632.jpg
I think its sitting a little low in front, which is kind of where we started. Maybe new springs will help. If not, maybe a small spacer in front would help.

That said, I think I'd have to be crawling or hit something really hard to get the shocks to move more than 2" right now.
 
If you do a spacer, think of it as temporary. The spring is sagging and a spacer only masks that fact.
Oh yeah. New springs come first.

I figured I'd go with the Moogs just because they're inexpensive and easy to get. Any reason not to get them?
 
Yeah. Axle pad to bump stop cap is about 3", maybe a little less. Exposed shock shaft is about 2.5".
View attachment 46505 View attachment 46506
I think its sitting a little low in front, which is kind of where we started. Maybe new springs will help. If not, maybe a small spacer in front would help.

That said, I think I'd have to be crawling or hit something really hard to get the shocks to move more than 2" right now.
Regardless of the ride height, your front shocks are acting as the bump stop. The front bumps are about .75" too short. What is happening in the rear?

I still suspect that the shocks are a bit too long for your ride height. Current and intended.
 
Oh yeah. New springs come first.

I figured I'd go with the Moogs just because they're inexpensive and easy to get. Any reason not to get them?
No reason not to. They ride great and definitely soak up bumps much better than the stockers. The rears also hold up under load better, if you load yours up you'll definitely notice.
If you are planning on using a spacer with new springs, may as well buy some 2" springs. I run the BDS coils and they ride very nice with 5000X shocks.
 
If you are planning on using a spacer with new springs, may as well buy some 2" springs. I run the BDS coils and they ride very nice with 5000X shocks.

Interesting. I was only thinking of a spacer as a correction, not as a lift per se. I might put a lift kit on in the future, but not today.

Also, I think I'd worry that the current shocks might not have enough stroke for a 2" lift.
 
Interesting. I was only thinking of a spacer as a correction, not as a lift per se. I might put a lift kit on in the future, but not today.

Spacers are a lift. As long as the bump stops don't allow the coils to become solid, then there isn't much difference between lift coils and spacers.

Also, I think I'd worry that the current shocks might not have enough stroke for a 2" lift.


Remind us of the total travel of your shocks? The amount of up travel you have suggests that they could use some added lift to get you back to ~4" of up.
 
Remind us of the total travel of your shocks? The amount of up travel you have suggests that they could use some added lift to get you back to ~4" of up.

RS999128 front: 7.062"
RS999240 rear: 6.375"
 
I like these better for stock ride height. More travel, less front bump stop required.

Rancho RS55128 front and rear
13.05" compressed
7.95" travel

Compared to
RS999128 front
13.438" compressed
7.062" travel

RS999240 rear
12.875" compressed
6.375" travel

Earlier I said I thought rs9000s are long with short travel. They are.
 
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Lol with all the hard work that you just did.

I was just guessing at the free spring length and got it wrong. What's a factor of 2 among friends, tho? :D

I did measure how much the suspension settled with my fat ass in the driver's seat, and using that I get closer to 160lbs/in, which is in the right ballpark.
 
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What is happening in the rear?

Things look a lot more normal. Here's how much travel I used on the rear shocks while running errands around town the other day.
IMAG0666.jpg
For comparison, I pretty much topped out the front shocks on the same trip.

On the same trip, I strapped a GoPro on the front bumper and got some footage of the front suspension in action. It's one of the most boring videos I've ever seen. There's not as much going on there as you might think. Nearly all the time, the axle is within 1/2" or so of its resting position. The axle only touches the bump stop once or twice on big dips, like driveway entrances and exits.
 
If anyone is still interested, I removed the front springs and did the bump stop check this weekend. I'll post a full write-up with pics later, but there are a couple highlights for this thread.

First, the free length of the front springs is currently right at 17". I don't know what the free length of the stock springs is, but the Moog replacements are 17.25". If the stock springs were supposed to be the same length, this would be the smoking gun.
IMAG0736.jpg

Also, @jjvw is right. The front shocks are long enough that they're fully compressed before the axle pad hits the bump stop. The gap at the axle pad at that point is about 3/4".
IMAG0740.jpg IMAG0742.jpg

However, I have 31x10.5R15 tires, and those hit the fender before the shock is fully compressed. Here's the gap at the axle pad with the steering at full lock and the tire just scuffing the fender. (I had the marshmallow in because my friend didn't believe that it would fully compress.)
IMAG0743.jpg
There was a little more room with the tires straight ahead. But worst case, I need 1" more bump stop for my tires.

I plan to keep the 31s, even if I eventually add a lift kit (thanks to the 31" tires with 2-3" lifts? thread!). Fortunately, a regulation hockey puck is 1". So I plan to bolt some hockey pucks on to the axle pads, which should do it. That will give me just enough room for the tires with the steering straight ahead, and should keep the tires from hitting the fenders hard even if I have the wheels turned.

Stay tuned for full walk-thrus of the Moog spring swap and bump stop check with pics.
 
Pretty interesting that 31s need bump stop extension, isn't it? Very few seem to have figured that out.

Nicely done.
 
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After a couple weeks of ordering parts and crawling around under the Jeep, I finished swapping in the Moog 3226 (front) and 3227 (rear) springs. Moog says these springs are for Rubicon models, but comparing to my old springs, I figure they're either for all 4.0L models or 4.0L with AT — basically the heavier stock Jeeps.

Here's what the front springs and shocks looked like before the install, with springs sitting at 11" and shocks at 2.5" of free stroke:
IMAG0700.jpg IMAG0696.jpg

And here's where the front springs and shocks are now after the install, with springs at 12" (stock height) and shocks at 3.5" of free stroke:
IMAG0904.jpg IMAG0902.jpg
For my Rancho RS999128 front shocks, that puts them right in the middle of their 7" stroke.

It's a similar story for the rear springs. Here's where I started:
IMAG0909.jpg IMAG0913.jpg

And here's where the rear springs and shock ended up after the Moog install:
IMAG1027.jpg IMAG1029.jpg

Here's how the Jeep looks after the install, sitting on 31s.
IMAG1031.jpg

If the Moog springs are supposed to sit at stock height (which seems so) for a stock vehicle, which is what I have, then we can certainly say the old springs were sagging.

As @Jerry Bransford suggested, I checked everything I could while I was under the Jeep, and found a couple more things to replace. I swapped out the original spring isolators. The rear ones were really beat up, and although the front ones weren't looking too bad, I figured for a couple bucks I might as well get new rubber. I got fresh marshmallows for the jounce bumpers because I thought it might help.

I also found that the rubber bushings and boots on the sway bar links were totally shot. So a swapped in a new set of sway bar links:
IMAG0706.jpg IMAG0895.jpg IMAG0892.jpg

Overall, this was a HUGE improvement in ride quality, which I would guess is largely due to the new isolators and the new sway bar links. But getting springs at the right height with the right elasticity probably helped too.

Thanks to everyone on this thread for the suggestions and advice!
 
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