I have a 2000 Grand Cherokee Limited with full time 4WD. It doesn't work when it's in AWD (4 wheel drive high) but works when it's in 4lo. Anybody know what's wrong in the transfer case? Clutch packs? Snow is coming soon and I need to fix it!
You have an NV247 transfer case. You don't have AWD. The NV247 sends power only to the rear wheels (that's 2WD) until one or both rear wheels lose traction. Loss or rear traction causes the NV247 to send power to the front. In that case I guess that it could be called AWD, but 4WD is probably best. With an NV247 you have either Quadra-Trac II or possibly Quadra-Drive. Most QTII WJs come with open differentials, so if one rear wheel loses traction followed by loss of traction by one of the front wheels, you get stuck. QD has the additional feature of Vari-Loc (a type of limited slip) differentials. Usually, when one wheel on an axle with Vari-Loc loses traction, torque is still applied to the other wheel. Because of the NV247 transfer case, when one rear wheel loses traction, even with Vari-Loc, there is still transfer of power to the front.
Now, what system do you have? Explain what's happening that makes you think it's not working.
Also, with the 247 transfer case used in both Quadratrac II and QuadraDrive applications, if it gets worn out, it will simply not transfer torque forward. The 4-low function bypasses the regular means by which the transfer case transfers torque. It's more like the older style design where it's an actual low-lock. This is why you can actually lock it in 4-low. It's possible the t-case is worn. I don't know much about their design or maintenance though. Is this a clutch pack system like the 249? Does anyone know?
I guess the correct term is full time 4wd? It has the quadradrive. I think it is not working because if I am in loose gravel, soft dirt, wet pavement etc. and give it gas, the rear wheels slip. The front wheels do nothing. I can powerbrake the thing if I want to. If I put it in 4lo it does not do that and it gets traction. I know it's not working as it should in 4high.
I was under the impression I have the 249?...but I do not really know what I am talking about!
The 249 was only used in ZJs. The 247 uses a clutch pack like a posi diff to transfer power forward. It's possible that it's worn out. Because 4lo still works, it's one of those cases of "fix it only if you have a reason to". In other words, if it doesn't present an issue in normal driving, you don't really need to worry about it.
The NV247 (QTII and QD) uses a gerotor pump/clutch pack system (called a progressive coupler or simply PC)) very similar to the system used in the Vari-Loc differentials. It requires a special fluid available only at the dealership (Mopar NV247 transfer case lube). It would be a good idea to change out the fluid (it takes a little less that 2 qts), because I doubt that you know what's in there. If after changing to the correct fluid and driving for a few days to work the good stuff into the clutch pack, you are still able to break the rear wheels free without the front wheels turning, the PC needs to be replaced. Keep in mind that in order to send power to the front wheels, the rear drive shaft will need to be turning faster than the front because that speed difference is what powers the gerotor pump and applies pressure to the clutch pack.