gas tank causes suspension sag? - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 15 Old 12-23-2011, 05:44 PM Thread Starter
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gas tank causes suspension sag?

after installing my 2.5 rk max travel kit and after driving around and a couple of minor wheeling trips to let the springs settle it seems that the rear pass corner is sagging about half an inch or so compared to the other corners with 1/4 tank of gas.

im sure this is a common thing, but very annoying. does anyone know if rock krawler designs their rear springs with the gas tank in mind? might i have put the rear springs in "backwards?" would swapping the rear springs around possibly do anything?

thanks.
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post #2 of 15 Old 12-23-2011, 05:55 PM
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That would be a good question for Rock Krawler.

On mine, the stock rear springs each have the same part number, indicating no compensation for the gas tank.
Also, my JK weighs the same left and right with half a tank of gas, further indicating no need to compensate.

The front springs are not exactly the same, the right one being one digit higher in the last part number position. (Maybe to compensate for the high torque of the 3.8!)
Each front wheel is supporting the same weight there, too.

Last edited by ronjenx; 12-23-2011 at 06:04 PM.
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post #3 of 15 Old 12-23-2011, 06:06 PM Thread Starter
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ya, im gonna give them a phone call next monday (after christmas). just wondering if anyone here had any info for my impatient ass.
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post #4 of 15 Old 12-25-2011, 02:46 PM
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Is it sagging with someone in the drivers seat?
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post #5 of 15 Old 12-25-2011, 03:15 PM
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Interesting. We have two JKs with 4.5" BDS coils. I just replaced the rear passenger coil under warranty with BDS on one rig and now my other JK is showing signs of the same.

The first one was 1" lower on the passenger side. Even had a BDS rep measure on flay ground the distance between the tire and fender on both sides, center of wheel to fender and the distance from bottom shock mount to that of the top shock mount. They confirmed the sag and ordered a replacement coil.


I also noticed that my right rear bottoms out before the drivers side does when lightly loaded.

Hmmm.
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post #6 of 15 Old 12-25-2011, 03:39 PM
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Yea the JK has a lean to the right from the gas tank.

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post #7 of 15 Old 12-25-2011, 03:46 PM
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It's not just the JK. The TJ exhibited the same issue. It has to do with torque while going down the road. It puts more pressure on that corner and this eventually happens. It seems to happen less in long arm rigs.


To visualize it, think of a high horsepower car on slicks at a drag strip. You can see it roll the car to the passenger rear. Same is happening to your jeep. So basically, your JK has too much power.

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post #8 of 15 Old 12-25-2011, 06:05 PM
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Pretty common on SWB Jeeps, more pronounced on JKs, called the "JK Lean". Caused by normal torque loading, plus the weight of the JK's tank and fuel. Easiest way to compensate for it is to put an extra 1/2" of spacer on the right rear spring. No more problems.

Last edited by SoK66; 12-26-2011 at 01:20 PM.
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post #9 of 15 Old 12-25-2011, 06:11 PM Thread Starter
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the torquing thing makes perfect sense. when i get on the gas at a stop sign it torques HARD compared to before it was lifted. i guess ill have to get a spacer, as much as that irritates me.
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post #10 of 15 Old 12-26-2011, 07:29 AM Thread Starter
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Quote:
Originally Posted by oz97tj View Post
So basically, your JK has too much power.
i dont think this is the problem with mine.
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post #11 of 15 Old 12-26-2011, 01:33 PM
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Quote:
Originally Posted by damon.l View Post
the torquing thing makes perfect sense. when i get on the gas at a stop sign it torques HARD compared to before it was lifted. i guess ill have to get a spacer, as much as that irritates me.
Torque has a minor effect on JKs. To remove lean a common remedy on any vehicle with a spring suspension has been to reverse the rear springs. When I did this on my TF 4" suspension it made no difference, maybe even made it a bit worse. Adding an extra 1/2" of spacer on the right rear cured it. (TF suspensions come with 1/2" front & rear spacers.) With the added spacer installed and roughly 4 gals. in the tank it measures about 1/8" taller on the right, with a full tank it measures about 1/8" lower. The weight transfer even has a slight affect on steering wheel alignment.

All this does illustrate the fact that Jeep should have found a way to keep the tank behind the rear axle.
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post #12 of 15 Old 12-26-2011, 01:51 PM
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Quote:
Originally Posted by SoK66 View Post
All this does illustrate the fact that Jeep should have found a way to keep the tank behind the rear axle.
I maintain there is no connection between the fuel tank and the JK leaning to the right.
Nobody has mentioned that theirs leans with a full tank and not with an empty tank.

Mine is pretty much stock, and doesn't lean.
Additionally, with half a tank of fuel, the left and right weights are equal.

Could my stock JK be different from all the others?

Last edited by ronjenx; 12-26-2011 at 01:53 PM.
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post #13 of 15 Old 12-26-2011, 02:26 PM Thread Starter
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Quote:
Originally Posted by ronjenx View Post
Nobody has mentioned that theirs leans with a full tank and not with an empty tank.
ill have to make sure to take measurements when i run it down to empty and after i top it off. ill be sure to post here.
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post #14 of 15 Old 12-26-2011, 04:04 PM
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Quote:
Originally Posted by ronjenx View Post
Nobody has mentioned that theirs leans with a full tank and not with an empty tank.
I did in another tread on this subject. 1/2" spacer in the right rear cures this completely. As I mentioned above, swapping the springs side to side made no difference, so it's not a spring fatigue issue but instead a result of unequal weight side to side. Pretty well documented that the lean, usually about 1/2" is caused by the weight of the tank and fuel loading.
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post #15 of 15 Old 12-26-2011, 04:10 PM
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Quote:
Originally Posted by SoK66 View Post
I did in another tread on this subject. 1/2" spacer in the right rear cures this completely. As I mentioned above, swapping the springs side to side made no difference, so it's not a spring fatigue issue but instead a result of unequal weight side to side. Pretty well documented that the lean, usually about 1/2" is caused by the weight of the tank and fuel loading.
That still leaves me wondering why mine has equal weight side to side, (1/2 full tank), doesn't lean, and 3 other JK's that I work on don't lean.

I'll take some measurements on mine, with nearly empty and full tank.

Last edited by ronjenx; 12-26-2011 at 04:13 PM.
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