jerking after lifting off gas pedal

jeepkj02 · **Posted:** Wed Aug 05, 2009 8:20 pm

I have this problem with the Jeep, when the engine is cold (i.e, hasn't been driven within one hour) and I'm driving and lift off the gas pedal (coast) the Jeep jerks, but after driving for a few minutes this goes away. This just happened today, only drove it twice in the city (under 45mph).

Jeep is a 02 with approx 84K miles.

Murphyman · **Posted:** Wed Aug 05, 2009 8:54 pm

Sorry, this doesn't have anything to do with that... But I see in your sig you are getting BDS front, 15" wheels, and Treadwrights. You definately know where it's at :wink:

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Something related to that, my Dodge Stratus I just sold did something similar. Would jerk around when letting off, as well as accelerating. Almost like it was trying to catch the right gear. Does the "jump" resemble that of a novice stick driver?

jeepkj02 · **Posted:** Wed Aug 05, 2009 9:04 pm

Murphyman wrote:

Sorry, this doesn't have anything to do with that... But I see in your sig you are getting BDS front, 15" wheels, and Treadwrights. You definately know where it's at :wink:

.

That's the plan! I really hope I can get a job before the winter because I want some new tires for the winter!

Murphyman wrote:

Something related to that, my Dodge Stratus I just sold did something similar. Would jerk around when letting off, as well as accelerating. Almost like it was trying to catch the right gear. Does the "jump" resemble that of a novice stick driver?

Sort of, but it only happens for the first few minutes of driving then goes away. Kind of weird.

Murphyman · **Posted:** Wed Aug 05, 2009 9:11 pm

Definately get that ultra-grip stuff that Treadwright offers. I heard it helps a lot in snow and ice. I didn't do it, and will prob regret it. Going to school in the Appalachian Mountains, oh boy.

But my Stratus was the same way. If it was the first time of the day to drive in it, then it would do it moody jump stuff a couple of times. Until I had been driving it for a good 10 or 15 min. I sold it so I don't really know what was up. I'm curious to see what the Tech Know-It-Alls chime in to say haha.

jeepkj02 · **Posted:** Wed Aug 05, 2009 10:34 pm

Hope its nothing serious. :evil:

Jeep4me99 · **Posted:** Wed Aug 05, 2009 10:48 pm

possibly transmission fluid level? does it happen at a specific RPM while you are decelerating? Mine did......always when the engine down shifted while coasting, can't recall the specific RPM on the tach it did it at, but the needle would jump.

If the jerking continues. remove hand from crotch. :wink:

jeepkj02 · **Posted:** Wed Aug 05, 2009 10:58 pm

Jeep4me99 wrote:

possibly transmission fluid level? does it happen at a specific RPM while you are decelerating? Mine did......always when the engine down shifted while coasting, can't recall the specific RPM on the tach it did it at, but the needle would jump.

If the jerking continues. remove hand from crotch. :wink:

I'll check the level tomorrow and see if it does it at a specific RPM. Only drove it for like 10 minutes today.

ATXKJ · **Posted:** Thu Aug 06, 2009 7:22 am

Check around the rear diff - the control arms - the upper ball joint - look for things loose - and listen for diff sounds.

The rear is the place where there's a significant torque loading change from acceleration to deceleration,
going away after it warms up sounds like oil warming up although normally on differential problems it's a noise.

jeepkj02 · **Posted:** Thu Aug 06, 2009 9:07 am

ATXKJ wrote:

Check around the rear diff - the control arms - the upper ball joint - look for things loose - and listen for diff sounds.

The rear is the place where there's a significant torque loading change from acceleration to deceleration,
going away after it warms up sounds like oil warming up although normally on differential problems it's a noise.

I checked the fluid (on a cold engine, sat overnight) normally it is right in the middle of the crosshatched area (safe area), but now it is on the top border of the safe area. The manual says to let the engine run for 5 minutes and then let it sit for 10 minutes before checking.

Another thing is that my rear ride height has a one inch difference from the left and right wheels. Been like that since I but on the lift. Both sides are the EXACT same. OME medium springs, one extra upper iso pad and RSX shocks.

The bushings and ball joint rear upper tri-link look very dry. Bushings are cracked and the BJ has no grease in it. (most of my other bushings are dried out too)

ATXKJ · **Posted:** Thu Aug 06, 2009 6:59 pm

Well the height thing bugs me - (you might measure actual spring length) but that shouldn't make a sound.

The standard rear suspension sound is a clunk from the upper shock mount - many shocks need washers between the shock and mount to take out the slop.

I was thinking differential oil - not engine -
the differential is where acceleration is on one side of the gear teeth and deceleration hits the other side of the teeth -
however if there's a problem - it normally makes a continuing noise - a whine that changes with speed.

on bushings - I don't think dried by itself is a problem - loose would be - as would loose U joints or a loose engine mounts

but most of the things I can thing of - would be consistent over the drive - to get something that happens when cold but not warm - it sounds like a fluid - check all of them - eng, tranny, diffs, transfer case

jeepkj02 · **Posted:** Thu Aug 06, 2009 7:39 pm

Bushings are dry and some are starting to crack.

Checked the engine and tranny oil today, level and condition looked good. I'll check the diffs and t-case.
EDIT: checked the rear diff, it was a bit overfilled, let it drain out of the fill plug.

The rear U-joint (diff side) is leaking grease, I wiped it down with some break cleaner and see if it continues to leak.

About the rear ride height.

From top unibody to perch is 1" difference
Shocks has 1/2" difference
Center hub to flare has 1" difference
From bottom of rear unibody LCA mount is 1" difference

Gas tank is about 1/2 full and this is in my garage. Nothing is loaded in the back of the Jeep. The front end is level.

jerking after lifting off gas pedal

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