Strange feeling after lift - is it normal

[tengg2001]

Hi all,

Not sure if this is normal:

I installed my lift (Mopar 2.5 inch).
Now every when I start to drive:
1. Start engine. Foot on Brake.
2. Shift gear to Drive.

When my foot is still on brake, and once shifting to drive, I can feel the rear suspension will getting higher. Once release the brake and moving, it will back to normal.. I'm wondering if this is somehow an expected behavior?

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[Dyolfknip74]

Putting the jeep into drive isn't changing the height of your lift. You are just feeling the tranny a bit more due to different center of gravity.

 

[BDinTX]

Are you sure your upper and lower control arms are torqued correctly?

 

[Kreepin1]

I don't have any experience since I haven't lifted my JLR, but I suspect you are feeling the normal effects of the new suspension geometry. The rear links are at a new angle and have increased "anti-squat." If the rear tires are allowed to rotate forward some of the push on the arms is vertical and raises the rear of the Jeep. For this to happen the rear brakes would have to slip. Try it again with the parking brake set hard and try it with your foot really mashing the brakes before shifting into gear. I bet it doesn't do it then...

 

[Kreepin1]

I forgot to mention, there are geometry correction brackets that lower the lower arms frame mounting point. My buddy with a JK loves the way his Jeep handles with them.

 

[tengg2001]

Are you sure your upper and lower control arms are torqued correctly?

That's my first suspicion too, but I re-torqued them after the installation, will probably check again. But if it's not torqued correctly, why would it it causing the issue?

 

[tengg2001]

If the rear tires are allowed to rotate forward some of the push on the arms is vertical and raises the rear of the Jeep.

I think that's probably it.. but why?

 

[Kreepin1]

I think that's probably it.. but why?

Look at the Jeep from the side and imagine extending the upper and lower control arms until they intersect. This point is the rear suspension's "instant center." The force of the ground pushing against the tire acts through this point so think of it being like a great big hand grabbing your Jeep and pulling at this spot.

Now, there is another imaginary point that represents all the Jeep's weight (or more accurately, it's mass). This point is called the "center of mass." Imagine another great big hand grabbing your Jeep at this point and holding it back (inertia).

If the instant center is lower than the center of mass when the two hands pull opposite directions the front of the Jeep will rise and the rear will drop. This is called "squat." If the instant center is higher than the center of mass when the two hands pull the rear of the Jeep will rise and the front will drop. This is called "anti-squat."

This is most noticeable at night. When you accelerate do your headlights climb higher or drop lower? If they drop then you have anti-squat and geometry correction brackets will lower the front of your lower control arm and lower the instant center a lot. My stock JK and JL both have some squat. Lifted Jeeps will have anti-squat without correction.

What is happening to you is similar, but the second great big hand is grabbing your Jeep where the instant center for the front suspension is and the force from the front tires/brakes is acting through this point.

Next time, let's talk about suspension flex and rear steer...

 

[BDinTX]

That's my first suspicion too, but I re-torqued them after the installation, will probably check again. But if it's not torqued correctly, why would it it causing the issue?

I don't know that it would cause what you're experiencing but if the bolts were loose and shifting around in the holes you would probably feel it.

 

[tengg2001]

I don't know that it would cause what you're experiencing but if the bolts were loose and shifting around in the holes you would probably feel it.

Oh i see. It might be not exactly the torque value, but definitely not loose. Is it possibly that I torqued the control arms on a jack stand, causing some binding issues..

 

[Kreepin1]

Oh i see. It might be not exactly the torque value, but definitely not loose. Is it possibly that I torqued the control arms on a jack stand, causing some binding issues..

If so you should loosen and re-torque the track bar and control arm bolts with the Jeep resting on the tires.

 

[tengg2001]

If so you should loosen and re-torque the track bar and control arm bolts with the Jeep resting on the tires.

Rear upper control arm axle side bolt is hidden behind the rotor. Do you know how people usually tighten that bolt?

 

[lowmpg]

That seems wrong. You shouldn't feel anymore slop in the drivetrain than when it was stock if everything is on correctly. It is normal to feel the drivetrain engage, but you should have noticed that in stock form.

 

[Pig-Pen]

its called pre-loading the suspension. its a common drag technique.

this is a 392 right?

 

[tengg2001]

its called pre-loading the suspension. its a common drag technique.

this is a 392 right?

I wish : )
It's regular Rubicon 4 door

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