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Unread 08-21-2004, 11:21 PM   #1
Deanwa
Registered User
 
Join Date: Aug 2004
Posts: 6
Vibration (Rumble) only under acceleration

Asking for ideas or help.

2004 Grand Cherokee. 4.0 Auto. All stock. 14,000 Mi. This is the model with the Part Time/Full Time four wheel drive.

There is a rumble/vibration that seems to come from about the area of the rear drive shaft, and occurs only when accelerating in overdrive and above 55 MPH. It is mostly a deep oscillating rumble that can be heard more then felt. It only does it when you are stepping on the gas and it gets a little louder when you accelerate harder. I would almost think it was exhaust noise but it rumbles and oscillates too much to be normal.

I suspect a drive shaft or u-joint issue but I am unsure why it only does it while accelerating.

Any and all help would be greatly appreciated!

PS,
While checking things out underneath, I noticed that the front driveshaft does not turn freely by hand even when in 2 wheel drive. Is this normal? I was thinking that it should have automatic locking hubs that dis-engage when in 2WD.

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Unread 08-22-2004, 12:17 PM   #2
driabyor
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1994 ZJ 
 
Join Date: Apr 2004
Location: chilton-haynes<$20
Posts: 2,450
tires?
a bad tire...... belts separating.... out of balance

mud?
mud stuck to the inside of wheel

wheel weights?
have they come off

bent drive shaft? block the front tires then jack the rear up put the jeep in neutral and slowly turn and look for a small deflection in the drive shaft.....

turning of drive shaft?
i dont think that it will turn unless the front wheels are off the ground... I think that it only disconnects in the tranny......
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Unread 08-23-2004, 07:19 PM   #3
Deanwa
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Join Date: Aug 2004
Posts: 6
Update:

Update:

I noticed this problem while on vacation with a heay load in the jeep. Now that it is unloaded, it does not occur. I suspect that it has to do with the angle of the u-joints. I was loaded with 4 passengers and 300 lbs of gear for about 1800 miles.

Still wondering if this jeep has auto locking hubs or if the hubs are just always locked in. If anybody knows, please let me know. It is the model that has the choice of part-time 4wd, full-time 4wd or 2wd.

Thanks!

Dean

P.S. We went a ways up the Rubicon trail while at Lake Tahoe. What a lot of fun! (No we did not go all the way).






Quote:
Originally Posted by Deanwa
Asking for ideas or help.

2004 Grand Cherokee. 4.0 Auto. All stock. 14,000 Mi. This is the model with the Part Time/Full Time four wheel drive.

There is a rumble/vibration that seems to come from about the area of the rear drive shaft, and occurs only when accelerating in overdrive and above 55 MPH. It is mostly a deep oscillating rumble that can be heard more then felt. It only does it when you are stepping on the gas and it gets a little louder when you accelerate harder. I would almost think it was exhaust noise but it rumbles and oscillates too much to be normal.

I suspect a drive shaft or u-joint issue but I am unsure why it only does it while accelerating.

Any and all help would be greatly appreciated!

PS,
While checking things out underneath, I noticed that the front driveshaft does not turn freely by hand even when in 2 wheel drive. Is this normal? I was thinking that it should have automatic locking hubs that dis-engage when in 2WD.
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Unread 08-23-2004, 10:49 PM   #4
Meerkat
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1996 ZJ 
 
Join Date: Apr 2003
Location: Belle, WV
Posts: 4,930
Quote:
Originally Posted by Deanwa
Update:

I noticed this problem while on vacation with a heay load in the jeep. Now that it is unloaded, it does not occur. I suspect that it has to do with the angle of the u-joints. I was loaded with 4 passengers and 300 lbs of gear for about 1800 miles.

Still wondering if this jeep has auto locking hubs or if the hubs are just always locked in. If anybody knows, please let me know. It is the model that has the choice of part-time 4wd, full-time 4wd or 2wd.

Thanks!

Dean

P.S. We went a ways up the Rubicon trail while at Lake Tahoe. What a lot of fun! (No we did not go all the way).


Ok, from your description, you have the NP242 Selec-Trac transfer case.
What you don't have is locking hubs.
What you do have is open differentials front and rear, and a transfer case that functions (essentially) as an open differential between the front and rear axle.
What this means is:
2HI - The transfer case is (mechanically) disconnected from the front axle. Use without restriction.
4PT- The transfer case is connected (locked) to the front and rear axles. All slip in the linkage is between the tires and the road surface. Therefor this should only be used in ice, snow, sand, loose gravel, etc.
4FT - The transfer case is connected (but open) to the front and rear axles. Slip between the axles is allowed inside the transfer case. Use without restriction. Torque split is 48/52 front/rear.
N - Both axles are disconnected from the transfer case. Use for towing your Jeep.
4LO - Works the same as 4PT except the gear ratio is increased to 2.72:1, providing much more torque to the wheels. This should only be used on slippery surfaces at very low speeds.

HTH
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Unread 08-24-2004, 08:58 PM   #5
Deanwa
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Join Date: Aug 2004
Posts: 6
Thanks for the detailed and helpful information. Most of my 4x4s have been full-sized trucks with hubs that I keep turned out when not in use. It seems more effecient to have the front end fully disengaged while on the highway.

This is my first jeep and even though it is a base model, we have been very pleased with it's performance on and off-road. We have had it almost 1-year now. After driving a Ford Superduty 4x4 for many years, the jeep seems to fit down about any trail or creek bed. And it sure is a lot easier to turn around at the end of the trail!


Quote:
Originally Posted by wvd

Ok, from your description, you have the NP242 Selec-Trac transfer case.
What you don't have is locking hubs.
What you do have is open differentials front and rear, and a transfer case that functions (essentially) as an open differential between the front and rear axle.
What this means is:
2HI - The transfer case is (mechanically) disconnected from the front axle. Use without restriction.
4PT- The transfer case is connected (locked) to the front and rear axles. All slip in the linkage is between the tires and the road surface. Therefor this should only be used in ice, snow, sand, loose gravel, etc.
4FT - The transfer case is connected (but open) to the front and rear axles. Slip between the axles is allowed inside the transfer case. Use without restriction. Torque split is 48/52 front/rear.
N - Both axles are disconnected from the transfer case. Use for towing your Jeep.
4LO - Works the same as 4PT except the gear ratio is increased to 2.72:1, providing much more torque to the wheels. This should only be used on slippery surfaces at very low speeds.

HTH
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