buckwheat

hi all, i have an 02 grand cherokee limited 4.7 v8 and the full time 4wd no longer works, i changed the oil in the transfer case with the mopar oil and still didnt help.....any suggestions. i have no codes or idiot lights coming on either...any help would be appreciated. its a quadra drive system.

buckwheat

man, not all at once please!

xxlcherokee

Give more history

beefmobile

What do you mean full time 4x4 doesn't work?

It being a full time system and 4x4 only (NP249), that would mean nothing happens when you try to drive forward. I assume maybe you mean the front wheels aren't being powered?

How did you find that out? Did you put it on jack stands and put it in drive?

Have you tried putting it in 4Lo and seeing what happens?

Have you checked vacuum lines, u-joints, driveshaft, and shift linkage?

buckwheat

4wd low works fine, if i get in snow the back tires will spin all day and the fronts act like its a 2wd vehicle

dnuccio

theres a million things that could be wrong. we need more info.

has it ever worked?
does it make any odd noises?
do the front tires try to engage or is there nothing there?
when did you first notice it stop working?
etc etc

buckwheat

i bought it used and it has never worked, it makes no noises, seems like there's nothing there at all. no lights or codes show up either

beefmobile

It's almost like you're intentionally being vague...

You said 4lo works fine.....but the front wheels don't turn? That would mean that 4lo doesn't work fine...?

Have you checked vacuum lines, u-joints, driveshaft, and shift linkage?

SeriousOffroad

Failed viscous coupler.

buckwheat

4wd low works fine, if i get in snow the back tires will spin all day and the fronts act like its a 2wd vehicle when its in 4hi

xxlcherokee

What do you mean 4low works if you are stuck in snow the rear tires spin? If you were stuck in snow and only the rear tires spin that would indicate your 4WD was not working. Do you have a front driveshaft connected? Have you checked?

fantacmet

He should correct me if I'm wrong but I believe what he is getting at is the following.

In 4 low, all 4 will spin, but it will pull him out of the snow.

In 4 high only the rears spin, leaving him "out in the cold."

buckwheat

exactly fantacmet

SteveMongr

As previously stated, it's most likely the 'viscous coupler'. Common issue with quadradrive and behaves exactly as you describe.
Matching tire circumference and pressure is critical with the Quadra Drive.

xxlcherokee

Found this online.

When the front and rear wheels begin to rotate at relatively the same RPMs again, the liquid "deactivates," becomes less viscous and more liquid like, and as a result the front wheels/diff. disengage, and the van is powered again only or primarily by rear wheel drive.

VC Fail - Causes & Effects

A VC can fail in two basic ways: it can stop engaging altogether or it can remain constantly engaged (sometimes only at higher operating temps). VC fluid loss caused by leaking seals seems to be the most likely cause of a total failure of the VC to engage at all. When this happens, you never have 4 WD. The more insidious and costly failure occurs when the VC remains engaged when it should not be engaged. This can lead to destruction of the entire drive train, including the expensive transaxle.

There appear to be two primary causes for the VC to engage when it should not: (1) having tires that are not all the same size and wear (all 4 must be the same), and (2) age...VCs appear to have a nautural life span, at least where subjected to routine high operating temps. (One shop also claims that having a drive train that is not properly aligned also causes premature engagement, but this theory seems questionable.)

When tires of different wear or size are used, it causes the VC to engage prematurely or even constantly. It makes the VC "think" your wheels are slipping and that you need 4 WD. Premature or constant engagement of the VC, particularly at highway speeds, overheats the VC, thereby "cooking" the viscous fluid. Over time, this causes the properties of the fluid to change so that it engages the VC prematurely or even permanently, thereby stressing the other components of the drivetrain.

A typical scenario leading to a cooked VC would involve a syncro with tire sizes that vary slightly in treaddepth. The syncro is regularly driven at highway speeds for hours at a time over a period of time. Eventually, the driver notices binding in the drive train whenever she pulls off the highway into a gas station for gas. It may be subtle at first. Eventually, though, as the fluid gets cooked and ruined, the wheels seem to stiffen or bind much easier than before, and ultimately at the slightest turn of the wheel. When it gets bad, the drive train may lock up completely in the parking lot at very slow speed upon a relatively slight turn of the steering wheel. This total engagement of the drive train puts tremendous strain on the components of the drive train when the van is moving at speed under power. With continued use, the transaxle soon fails, the drive shaft and CV joints are also strained.

There is some dispute as to whether a properly functioning VC will cause binding in very tight turns, like when turning while backing out of a driveway, or doing a sharp turn in a parking lot. The VC engages when the front and rear wheels turn at different speeds, greater than 6% in relative RPMs. When the front and rear wheels turn at a greater difference in RPMs during sharp turns (above 6%), it would seem that the VC would engage and cause some binding. However, a brand new VC will not do this, even when warm.